// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:ui' as ui show ImageFilter, Gradient, Image, Color;

import 'package:flutter/animation.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/semantics.dart';

import 'package:vector_math/vector_math_64.dart';

import 'box.dart';
import 'layer.dart';
import 'layout_helper.dart';
import 'mouse_cursor.dart';
import 'mouse_tracking.dart';
import 'object.dart';

export 'package:flutter/gestures.dart' show
  PointerEvent,
  PointerDownEvent,
  PointerMoveEvent,
  PointerUpEvent,
  PointerCancelEvent;

/// A base class for render boxes that resemble their children.
///
/// A proxy box has a single child and simply mimics all the properties of that
/// child by calling through to the child for each function in the render box
/// protocol. For example, a proxy box determines its size by asking its child
/// to layout with the same constraints and then matching the size.
///
/// A proxy box isn't useful on its own because you might as well just replace
/// the proxy box with its child. However, RenderProxyBox is a useful base class
/// for render objects that wish to mimic most, but not all, of the properties
/// of their child.
///
/// See also:
///
///  * [RenderProxySliver], a base class for render slivers that resemble their
///    children.
class RenderProxyBox extends RenderBox with RenderObjectWithChildMixin<RenderBox>, RenderProxyBoxMixin<RenderBox> {
  /// Creates a proxy render box.
  ///
  /// Proxy render boxes are rarely created directly because they simply proxy
  /// the render box protocol to [child]. Instead, consider using one of the
  /// subclasses.
  RenderProxyBox([RenderBox? child]) {
    this.child = child;
  }
}

/// Implementation of [RenderProxyBox].
///
/// Use this mixin in situations where the proxying behavior
/// of [RenderProxyBox] is desired but inheriting from [RenderProxyBox] is
/// impractical (e.g. because you want to mix in other classes as well).
// TODO(ianh): Remove this class once https://github.com/dart-lang/sdk/issues/31543 is fixed
@optionalTypeArgs
mixin RenderProxyBoxMixin<T extends RenderBox> on RenderBox, RenderObjectWithChildMixin<T> {
  @override
  void setupParentData(RenderObject child) {
    // We don't actually use the offset argument in BoxParentData, so let's
    // avoid allocating it at all.
    if (child.parentData is! ParentData)
      child.parentData = ParentData();
  }

  @override
  double computeMinIntrinsicWidth(double height) {
    if (child != null)
      return child!.getMinIntrinsicWidth(height);
    return 0.0;
  }

  @override
  double computeMaxIntrinsicWidth(double height) {
    if (child != null)
      return child!.getMaxIntrinsicWidth(height);
    return 0.0;
  }

  @override
  double computeMinIntrinsicHeight(double width) {
    if (child != null)
      return child!.getMinIntrinsicHeight(width);
    return 0.0;
  }

  @override
  double computeMaxIntrinsicHeight(double width) {
    if (child != null)
      return child!.getMaxIntrinsicHeight(width);
    return 0.0;
  }

  @override
  double? computeDistanceToActualBaseline(TextBaseline baseline) {
    if (child != null)
      return child!.getDistanceToActualBaseline(baseline);
    return super.computeDistanceToActualBaseline(baseline);
  }

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    if (child != null) {
      return child!.getDryLayout(constraints);
    }
    return computeSizeForNoChild(constraints);
  }

  @override
  void performLayout() {
    if (child != null) {
      child!.layout(constraints, parentUsesSize: true);
      size = child!.size;
    } else {
      size = computeSizeForNoChild(constraints);
    }
  }

  /// Calculate the size the [RenderProxyBox] would have under the given
  /// [BoxConstraints] for the case where it does not have a child.
  Size computeSizeForNoChild(BoxConstraints constraints) {
    return constraints.smallest;
  }

  @override
  bool hitTestChildren(BoxHitTestResult result, { required Offset position }) {
    return child?.hitTest(result, position: position) ?? false;
  }

  @override
  void applyPaintTransform(RenderObject child, Matrix4 transform) { }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null)
      context.paintChild(child!, offset);
  }
}

/// How to behave during hit tests.
enum HitTestBehavior {
  /// Targets that defer to their children receive events within their bounds
  /// only if one of their children is hit by the hit test.
  deferToChild,

  /// Opaque targets can be hit by hit tests, causing them to both receive
  /// events within their bounds and prevent targets visually behind them from
  /// also receiving events.
  opaque,

  /// Translucent targets both receive events within their bounds and permit
  /// targets visually behind them to also receive events.
  translucent,
}

/// A RenderProxyBox subclass that allows you to customize the
/// hit-testing behavior.
abstract class RenderProxyBoxWithHitTestBehavior extends RenderProxyBox {
  /// Initializes member variables for subclasses.
  ///
  /// By default, the [behavior] is [HitTestBehavior.deferToChild].
  RenderProxyBoxWithHitTestBehavior({
    this.behavior = HitTestBehavior.deferToChild,
    RenderBox? child,
  }) : super(child);

  /// How to behave during hit testing.
  HitTestBehavior behavior;

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    bool hitTarget = false;
    if (size.contains(position)) {
      hitTarget = hitTestChildren(result, position: position) || hitTestSelf(position);
      if (hitTarget || behavior == HitTestBehavior.translucent)
        result.add(BoxHitTestEntry(this, position));
    }
    return hitTarget;
  }

  @override
  bool hitTestSelf(Offset position) => behavior == HitTestBehavior.opaque;

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(EnumProperty<HitTestBehavior>('behavior', behavior, defaultValue: null));
  }
}

/// Imposes additional constraints on its child.
///
/// A render constrained box proxies most functions in the render box protocol
/// to its child, except that when laying out its child, it tightens the
/// constraints provided by its parent by enforcing the [additionalConstraints]
/// as well.
///
/// For example, if you wanted [child] to have a minimum height of 50.0 logical
/// pixels, you could use `const BoxConstraints(minHeight: 50.0)` as the
/// [additionalConstraints].
class RenderConstrainedBox extends RenderProxyBox {
  /// Creates a render box that constrains its child.
  ///
  /// The [additionalConstraints] argument must not be null and must be valid.
  RenderConstrainedBox({
    RenderBox? child,
    required BoxConstraints additionalConstraints,
  }) : assert(additionalConstraints != null),
       assert(additionalConstraints.debugAssertIsValid()),
       _additionalConstraints = additionalConstraints,
       super(child);

  /// Additional constraints to apply to [child] during layout.
  BoxConstraints get additionalConstraints => _additionalConstraints;
  BoxConstraints _additionalConstraints;
  set additionalConstraints(BoxConstraints value) {
    assert(value != null);
    assert(value.debugAssertIsValid());
    if (_additionalConstraints == value)
      return;
    _additionalConstraints = value;
    markNeedsLayout();
  }

  @override
  double computeMinIntrinsicWidth(double height) {
    if (_additionalConstraints.hasBoundedWidth && _additionalConstraints.hasTightWidth)
      return _additionalConstraints.minWidth;
    final double width = super.computeMinIntrinsicWidth(height);
    assert(width.isFinite);
    if (!_additionalConstraints.hasInfiniteWidth)
      return _additionalConstraints.constrainWidth(width);
    return width;
  }

  @override
  double computeMaxIntrinsicWidth(double height) {
    if (_additionalConstraints.hasBoundedWidth && _additionalConstraints.hasTightWidth)
      return _additionalConstraints.minWidth;
    final double width = super.computeMaxIntrinsicWidth(height);
    assert(width.isFinite);
    if (!_additionalConstraints.hasInfiniteWidth)
      return _additionalConstraints.constrainWidth(width);
    return width;
  }

  @override
  double computeMinIntrinsicHeight(double width) {
    if (_additionalConstraints.hasBoundedHeight && _additionalConstraints.hasTightHeight)
      return _additionalConstraints.minHeight;
    final double height = super.computeMinIntrinsicHeight(width);
    assert(height.isFinite);
    if (!_additionalConstraints.hasInfiniteHeight)
      return _additionalConstraints.constrainHeight(height);
    return height;
  }

  @override
  double computeMaxIntrinsicHeight(double width) {
    if (_additionalConstraints.hasBoundedHeight && _additionalConstraints.hasTightHeight)
      return _additionalConstraints.minHeight;
    final double height = super.computeMaxIntrinsicHeight(width);
    assert(height.isFinite);
    if (!_additionalConstraints.hasInfiniteHeight)
      return _additionalConstraints.constrainHeight(height);
    return height;
  }

  @override
  void performLayout() {
    final BoxConstraints constraints = this.constraints;
    if (child != null) {
      child!.layout(_additionalConstraints.enforce(constraints), parentUsesSize: true);
      size = child!.size;
    } else {
      size = _additionalConstraints.enforce(constraints).constrain(Size.zero);
    }
  }

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    if (child != null) {
      return child!.getDryLayout(_additionalConstraints.enforce(constraints));
    } else {
      return _additionalConstraints.enforce(constraints).constrain(Size.zero);
    }
  }

  @override
  void debugPaintSize(PaintingContext context, Offset offset) {
    super.debugPaintSize(context, offset);
    assert(() {
      final Paint paint;
      if (child == null || child!.size.isEmpty) {
        paint = Paint()
          ..color = const Color(0x90909090);
        context.canvas.drawRect(offset & size, paint);
      }
      return true;
    }());
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<BoxConstraints>('additionalConstraints', additionalConstraints));
  }
}

/// Constrains the child's [BoxConstraints.maxWidth] and
/// [BoxConstraints.maxHeight] if they're otherwise unconstrained.
///
/// This has the effect of giving the child a natural dimension in unbounded
/// environments. For example, by providing a [maxHeight] to a widget that
/// normally tries to be as big as possible, the widget will normally size
/// itself to fit its parent, but when placed in a vertical list, it will take
/// on the given height.
///
/// This is useful when composing widgets that normally try to match their
/// parents' size, so that they behave reasonably in lists (which are
/// unbounded).
class RenderLimitedBox extends RenderProxyBox {
  /// Creates a render box that imposes a maximum width or maximum height on its
  /// child if the child is otherwise unconstrained.
  ///
  /// The [maxWidth] and [maxHeight] arguments not be null and must be
  /// non-negative.
  RenderLimitedBox({
    RenderBox? child,
    double maxWidth = double.infinity,
    double maxHeight = double.infinity,
  }) : assert(maxWidth != null && maxWidth >= 0.0),
       assert(maxHeight != null && maxHeight >= 0.0),
       _maxWidth = maxWidth,
       _maxHeight = maxHeight,
       super(child);

  /// The value to use for maxWidth if the incoming maxWidth constraint is infinite.
  double get maxWidth => _maxWidth;
  double _maxWidth;
  set maxWidth(double value) {
    assert(value != null && value >= 0.0);
    if (_maxWidth == value)
      return;
    _maxWidth = value;
    markNeedsLayout();
  }

  /// The value to use for maxHeight if the incoming maxHeight constraint is infinite.
  double get maxHeight => _maxHeight;
  double _maxHeight;
  set maxHeight(double value) {
    assert(value != null && value >= 0.0);
    if (_maxHeight == value)
      return;
    _maxHeight = value;
    markNeedsLayout();
  }

  BoxConstraints _limitConstraints(BoxConstraints constraints) {
    return BoxConstraints(
      minWidth: constraints.minWidth,
      maxWidth: constraints.hasBoundedWidth ? constraints.maxWidth : constraints.constrainWidth(maxWidth),
      minHeight: constraints.minHeight,
      maxHeight: constraints.hasBoundedHeight ? constraints.maxHeight : constraints.constrainHeight(maxHeight),
    );
  }

  Size _computeSize({required BoxConstraints constraints, required ChildLayouter layoutChild }) {
    if (child != null) {
      final Size childSize = layoutChild(child!, _limitConstraints(constraints));
      return constraints.constrain(childSize);
    }
    return _limitConstraints(constraints).constrain(Size.zero);
  }

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    return _computeSize(
      constraints: constraints,
      layoutChild: ChildLayoutHelper.dryLayoutChild,
    );
  }

  @override
  void performLayout() {
    size = _computeSize(
      constraints: constraints,
      layoutChild: ChildLayoutHelper.layoutChild,
    );
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DoubleProperty('maxWidth', maxWidth, defaultValue: double.infinity));
    properties.add(DoubleProperty('maxHeight', maxHeight, defaultValue: double.infinity));
  }
}

/// Attempts to size the child to a specific aspect ratio.
///
/// The render object first tries the largest width permitted by the layout
/// constraints. The height of the render object is determined by applying the
/// given aspect ratio to the width, expressed as a ratio of width to height.
///
/// For example, a 16:9 width:height aspect ratio would have a value of
/// 16.0/9.0. If the maximum width is infinite, the initial width is determined
/// by applying the aspect ratio to the maximum height.
///
/// Now consider a second example, this time with an aspect ratio of 2.0 and
/// layout constraints that require the width to be between 0.0 and 100.0 and
/// the height to be between 0.0 and 100.0. We'll select a width of 100.0 (the
/// biggest allowed) and a height of 50.0 (to match the aspect ratio).
///
/// In that same situation, if the aspect ratio is 0.5, we'll also select a
/// width of 100.0 (still the biggest allowed) and we'll attempt to use a height
/// of 200.0. Unfortunately, that violates the constraints because the child can
/// be at most 100.0 pixels tall. The render object will then take that value
/// and apply the aspect ratio again to obtain a width of 50.0. That width is
/// permitted by the constraints and the child receives a width of 50.0 and a
/// height of 100.0. If the width were not permitted, the render object would
/// continue iterating through the constraints. If the render object does not
/// find a feasible size after consulting each constraint, the render object
/// will eventually select a size for the child that meets the layout
/// constraints but fails to meet the aspect ratio constraints.
class RenderAspectRatio extends RenderProxyBox {
  /// Creates as render object with a specific aspect ratio.
  ///
  /// The [aspectRatio] argument must be a finite, positive value.
  RenderAspectRatio({
    RenderBox? child,
    required double aspectRatio,
  }) : assert(aspectRatio != null),
       assert(aspectRatio > 0.0),
       assert(aspectRatio.isFinite),
       _aspectRatio = aspectRatio,
       super(child);

  /// The aspect ratio to attempt to use.
  ///
  /// The aspect ratio is expressed as a ratio of width to height. For example,
  /// a 16:9 width:height aspect ratio would have a value of 16.0/9.0.
  double get aspectRatio => _aspectRatio;
  double _aspectRatio;
  set aspectRatio(double value) {
    assert(value != null);
    assert(value > 0.0);
    assert(value.isFinite);
    if (_aspectRatio == value)
      return;
    _aspectRatio = value;
    markNeedsLayout();
  }

  @override
  double computeMinIntrinsicWidth(double height) {
    if (height.isFinite)
      return height * _aspectRatio;
    if (child != null)
      return child!.getMinIntrinsicWidth(height);
    return 0.0;
  }

  @override
  double computeMaxIntrinsicWidth(double height) {
    if (height.isFinite)
      return height * _aspectRatio;
    if (child != null)
      return child!.getMaxIntrinsicWidth(height);
    return 0.0;
  }

  @override
  double computeMinIntrinsicHeight(double width) {
    if (width.isFinite)
      return width / _aspectRatio;
    if (child != null)
      return child!.getMinIntrinsicHeight(width);
    return 0.0;
  }

  @override
  double computeMaxIntrinsicHeight(double width) {
    if (width.isFinite)
      return width / _aspectRatio;
    if (child != null)
      return child!.getMaxIntrinsicHeight(width);
    return 0.0;
  }

  Size _applyAspectRatio(BoxConstraints constraints) {
    assert(constraints.debugAssertIsValid());
    assert(() {
      if (!constraints.hasBoundedWidth && !constraints.hasBoundedHeight) {
        throw FlutterError(
          '$runtimeType has unbounded constraints.\n'
          'This $runtimeType was given an aspect ratio of $aspectRatio but was given '
          'both unbounded width and unbounded height constraints. Because both '
          'constraints were unbounded, this render object doesn\'t know how much '
          'size to consume.'
        );
      }
      return true;
    }());

    if (constraints.isTight)
      return constraints.smallest;

    double width = constraints.maxWidth;
    double height;

    // We default to picking the height based on the width, but if the width
    // would be infinite, that's not sensible so we try to infer the height
    // from the width.
    if (width.isFinite) {
      height = width / _aspectRatio;
    } else {
      height = constraints.maxHeight;
      width = height * _aspectRatio;
    }

    // Similar to RenderImage, we iteratively attempt to fit within the given
    // constraints while maintaining the given aspect ratio. The order of
    // applying the constraints is also biased towards inferring the height
    // from the width.

    if (width > constraints.maxWidth) {
      width = constraints.maxWidth;
      height = width / _aspectRatio;
    }

    if (height > constraints.maxHeight) {
      height = constraints.maxHeight;
      width = height * _aspectRatio;
    }

    if (width < constraints.minWidth) {
      width = constraints.minWidth;
      height = width / _aspectRatio;
    }

    if (height < constraints.minHeight) {
      height = constraints.minHeight;
      width = height * _aspectRatio;
    }

    return constraints.constrain(Size(width, height));
  }

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    return _applyAspectRatio(constraints);
  }

  @override
  void performLayout() {
    size = computeDryLayout(constraints);
    if (child != null)
      child!.layout(BoxConstraints.tight(size));
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DoubleProperty('aspectRatio', aspectRatio));
  }
}

/// Sizes its child to the child's maximum intrinsic width.
///
/// This class is useful, for example, when unlimited width is available and
/// you would like a child that would otherwise attempt to expand infinitely to
/// instead size itself to a more reasonable width.
///
/// The constraints that this object passes to its child will adhere to the
/// parent's constraints, so if the constraints are not large enough to satisfy
/// the child's maximum intrinsic width, then the child will get less width
/// than it otherwise would. Likewise, if the minimum width constraint is
/// larger than the child's maximum intrinsic width, the child will be given
/// more width than it otherwise would.
///
/// If [stepWidth] is non-null, the child's width will be snapped to a multiple
/// of the [stepWidth]. Similarly, if [stepHeight] is non-null, the child's
/// height will be snapped to a multiple of the [stepHeight].
///
/// This class is relatively expensive, because it adds a speculative layout
/// pass before the final layout phase. Avoid using it where possible. In the
/// worst case, this render object can result in a layout that is O(N²) in the
/// depth of the tree.
///
/// See also:
///
///  * [Align], a widget that aligns its child within itself. This can be used
///    to loosen the constraints passed to the [RenderIntrinsicWidth],
///    allowing the [RenderIntrinsicWidth]'s child to be smaller than that of
///    its parent.
///  * [Row], which when used with [CrossAxisAlignment.stretch] can be used
///    to loosen just the width constraints that are passed to the
///    [RenderIntrinsicWidth], allowing the [RenderIntrinsicWidth]'s child's
///    width to be smaller than that of its parent.
class RenderIntrinsicWidth extends RenderProxyBox {
  /// Creates a render object that sizes itself to its child's intrinsic width.
  ///
  /// If [stepWidth] is non-null it must be > 0.0. Similarly If [stepHeight] is
  /// non-null it must be > 0.0.
  RenderIntrinsicWidth({
    double? stepWidth,
    double? stepHeight,
    RenderBox? child,
  }) : assert(stepWidth == null || stepWidth > 0.0),
       assert(stepHeight == null || stepHeight > 0.0),
       _stepWidth = stepWidth,
       _stepHeight = stepHeight,
       super(child);

  /// If non-null, force the child's width to be a multiple of this value.
  ///
  /// This value must be null or > 0.0.
  double? get stepWidth => _stepWidth;
  double? _stepWidth;
  set stepWidth(double? value) {
    assert(value == null || value > 0.0);
    if (value == _stepWidth)
      return;
    _stepWidth = value;
    markNeedsLayout();
  }

  /// If non-null, force the child's height to be a multiple of this value.
  ///
  /// This value must be null or > 0.0.
  double? get stepHeight => _stepHeight;
  double? _stepHeight;
  set stepHeight(double? value) {
    assert(value == null || value > 0.0);
    if (value == _stepHeight)
      return;
    _stepHeight = value;
    markNeedsLayout();
  }

  static double _applyStep(double input, double? step) {
    assert(input.isFinite);
    if (step == null)
      return input;
    return (input / step).ceil() * step;
  }

  @override
  double computeMinIntrinsicWidth(double height) {
    return computeMaxIntrinsicWidth(height);
  }

  @override
  double computeMaxIntrinsicWidth(double height) {
    if (child == null)
      return 0.0;
    final double width = child!.getMaxIntrinsicWidth(height);
    return _applyStep(width, _stepWidth);
  }

  @override
  double computeMinIntrinsicHeight(double width) {
    if (child == null)
      return 0.0;
    if (!width.isFinite)
      width = computeMaxIntrinsicWidth(double.infinity);
    assert(width.isFinite);
    final double height = child!.getMinIntrinsicHeight(width);
    return _applyStep(height, _stepHeight);
  }

  @override
  double computeMaxIntrinsicHeight(double width) {
    if (child == null)
      return 0.0;
    if (!width.isFinite)
      width = computeMaxIntrinsicWidth(double.infinity);
    assert(width.isFinite);
    final double height = child!.getMaxIntrinsicHeight(width);
    return _applyStep(height, _stepHeight);
  }

  Size _computeSize({required ChildLayouter layoutChild, required BoxConstraints constraints}) {
    if (child != null) {
      if (!constraints.hasTightWidth) {
        final double width = child!.getMaxIntrinsicWidth(constraints.maxHeight);
        assert(width.isFinite);
        constraints = constraints.tighten(width: _applyStep(width, _stepWidth));
      }
      if (_stepHeight != null) {
        final double height = child!.getMaxIntrinsicHeight(constraints.maxWidth);
        assert(height.isFinite);
        constraints = constraints.tighten(height: _applyStep(height, _stepHeight));
      }
      return layoutChild(child!, constraints);
    } else {
      return constraints.smallest;
    }
  }

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    return _computeSize(
      layoutChild: ChildLayoutHelper.dryLayoutChild,
      constraints: constraints,
    );
  }

  @override
  void performLayout() {
    size = _computeSize(
      layoutChild: ChildLayoutHelper.layoutChild,
      constraints: constraints,
    );
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DoubleProperty('stepWidth', stepWidth));
    properties.add(DoubleProperty('stepHeight', stepHeight));
  }
}

/// Sizes its child to the child's intrinsic height.
///
/// This class is useful, for example, when unlimited height is available and
/// you would like a child that would otherwise attempt to expand infinitely to
/// instead size itself to a more reasonable height.
///
/// The constraints that this object passes to its child will adhere to the
/// parent's constraints, so if the constraints are not large enough to satisfy
/// the child's maximum intrinsic height, then the child will get less height
/// than it otherwise would. Likewise, if the minimum height constraint is
/// larger than the child's maximum intrinsic height, the child will be given
/// more height than it otherwise would.
///
/// This class is relatively expensive, because it adds a speculative layout
/// pass before the final layout phase. Avoid using it where possible. In the
/// worst case, this render object can result in a layout that is O(N²) in the
/// depth of the tree.
///
/// See also:
///
///  * [Align], a widget that aligns its child within itself. This can be used
///    to loosen the constraints passed to the [RenderIntrinsicHeight],
///    allowing the [RenderIntrinsicHeight]'s child to be smaller than that of
///    its parent.
///  * [Column], which when used with [CrossAxisAlignment.stretch] can be used
///    to loosen just the height constraints that are passed to the
///    [RenderIntrinsicHeight], allowing the [RenderIntrinsicHeight]'s child's
///    height to be smaller than that of its parent.
class RenderIntrinsicHeight extends RenderProxyBox {
  /// Creates a render object that sizes itself to its child's intrinsic height.
  RenderIntrinsicHeight({
    RenderBox? child,
  }) : super(child);

  @override
  double computeMinIntrinsicWidth(double height) {
    if (child == null)
      return 0.0;
    if (!height.isFinite)
      height = child!.getMaxIntrinsicHeight(double.infinity);
    assert(height.isFinite);
    return child!.getMinIntrinsicWidth(height);
  }

  @override
  double computeMaxIntrinsicWidth(double height) {
    if (child == null)
      return 0.0;
    if (!height.isFinite)
      height = child!.getMaxIntrinsicHeight(double.infinity);
    assert(height.isFinite);
    return child!.getMaxIntrinsicWidth(height);
  }

  @override
  double computeMinIntrinsicHeight(double width) {
    return computeMaxIntrinsicHeight(width);
  }

  Size _computeSize({required ChildLayouter layoutChild, required BoxConstraints constraints}) {
    if (child != null) {
      if (!constraints.hasTightHeight) {
        final double height = child!.getMaxIntrinsicHeight(constraints.maxWidth);
        assert(height.isFinite);
        constraints = constraints.tighten(height: height);
      }
      return layoutChild(child!, constraints);
    } else {
      return constraints.smallest;
    }
  }

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    return _computeSize(
      layoutChild: ChildLayoutHelper.dryLayoutChild,
      constraints: constraints,
    );
  }

  @override
  void performLayout() {
    size = _computeSize(
      layoutChild: ChildLayoutHelper.layoutChild,
      constraints: constraints,
    );
  }
}

/// Makes its child partially transparent.
///
/// This class paints its child into an intermediate buffer and then blends the
/// child back into the scene partially transparent.
///
/// For values of opacity other than 0.0 and 1.0, this class is relatively
/// expensive because it requires painting the child into an intermediate
/// buffer. For the value 0.0, the child is simply not painted at all. For the
/// value 1.0, the child is painted immediately without an intermediate buffer.
class RenderOpacity extends RenderProxyBox {
  /// Creates a partially transparent render object.
  ///
  /// The [opacity] argument must be between 0.0 and 1.0, inclusive.
  RenderOpacity({
    double opacity = 1.0,
    bool alwaysIncludeSemantics = false,
    RenderBox? child,
  }) : assert(opacity != null),
       assert(opacity >= 0.0 && opacity <= 1.0),
       assert(alwaysIncludeSemantics != null),
       _opacity = opacity,
       _alwaysIncludeSemantics = alwaysIncludeSemantics,
       _alpha = ui.Color.getAlphaFromOpacity(opacity),
       super(child);

  @override
  bool get alwaysNeedsCompositing => child != null && (_alpha != 0 && _alpha != 255);

  int _alpha;

  /// The fraction to scale the child's alpha value.
  ///
  /// An opacity of 1.0 is fully opaque. An opacity of 0.0 is fully transparent
  /// (i.e., invisible).
  ///
  /// The opacity must not be null.
  ///
  /// Values 1.0 and 0.0 are painted with a fast path. Other values
  /// require painting the child into an intermediate buffer, which is
  /// expensive.
  double get opacity => _opacity;
  double _opacity;
  set opacity(double value) {
    assert(value != null);
    assert(value >= 0.0 && value <= 1.0);
    if (_opacity == value)
      return;
    final bool didNeedCompositing = alwaysNeedsCompositing;
    final bool wasVisible = _alpha != 0;
    _opacity = value;
    _alpha = ui.Color.getAlphaFromOpacity(_opacity);
    if (didNeedCompositing != alwaysNeedsCompositing)
      markNeedsCompositingBitsUpdate();
    markNeedsPaint();
    if (wasVisible != (_alpha != 0) && !alwaysIncludeSemantics)
      markNeedsSemanticsUpdate();
  }

  /// Whether child semantics are included regardless of the opacity.
  ///
  /// If false, semantics are excluded when [opacity] is 0.0.
  ///
  /// Defaults to false.
  bool get alwaysIncludeSemantics => _alwaysIncludeSemantics;
  bool _alwaysIncludeSemantics;
  set alwaysIncludeSemantics(bool value) {
    if (value == _alwaysIncludeSemantics)
      return;
    _alwaysIncludeSemantics = value;
    markNeedsSemanticsUpdate();
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      if (_alpha == 0) {
        // No need to keep the layer. We'll create a new one if necessary.
        layer = null;
        return;
      }
      if (_alpha == 255) {
        // No need to keep the layer. We'll create a new one if necessary.
        layer = null;
        context.paintChild(child!, offset);
        return;
      }
      assert(needsCompositing);
      layer = context.pushOpacity(offset, _alpha, super.paint, oldLayer: layer as OpacityLayer?);
    }
  }

  @override
  void visitChildrenForSemantics(RenderObjectVisitor visitor) {
    if (child != null && (_alpha != 0 || alwaysIncludeSemantics))
      visitor(child!);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DoubleProperty('opacity', opacity));
    properties.add(FlagProperty('alwaysIncludeSemantics', value: alwaysIncludeSemantics, ifTrue: 'alwaysIncludeSemantics'));
  }
}

/// Implementation of [RenderAnimatedOpacity] and [RenderSliverAnimatedOpacity].
///
/// This mixin allows the logic of animating opacity to be used with different
/// layout models, e.g. the way that [RenderAnimatedOpacity] uses it for [RenderBox]
/// and [RenderSliverAnimatedOpacity] uses it for [RenderSliver].
mixin RenderAnimatedOpacityMixin<T extends RenderObject> on RenderObjectWithChildMixin<T> {
  int? _alpha;

  @override
  bool get alwaysNeedsCompositing => child != null && _currentlyNeedsCompositing!;
  bool? _currentlyNeedsCompositing;

  /// The animation that drives this render object's opacity.
  ///
  /// An opacity of 1.0 is fully opaque. An opacity of 0.0 is fully transparent
  /// (i.e., invisible).
  ///
  /// To change the opacity of a child in a static manner, not animated,
  /// consider [RenderOpacity] instead.
  ///
  /// This getter cannot be read until the value has been set. It should be set
  /// by the constructor of the class in which this mixin is included.
  Animation<double> get opacity => _opacity!;
  Animation<double>? _opacity;
  set opacity(Animation<double> value) {
    assert(value != null);
    if (_opacity == value)
      return;
    if (attached && _opacity != null)
      opacity.removeListener(_updateOpacity);
    _opacity = value;
    if (attached)
      opacity.addListener(_updateOpacity);
    _updateOpacity();
  }

  /// Whether child semantics are included regardless of the opacity.
  ///
  /// If false, semantics are excluded when [opacity] is 0.0.
  ///
  /// Defaults to false.
  ///
  /// This getter cannot be read until the value has been set. It should be set
  /// by the constructor of the class in which this mixin is included.
  bool get alwaysIncludeSemantics => _alwaysIncludeSemantics!;
  bool? _alwaysIncludeSemantics;
  set alwaysIncludeSemantics(bool value) {
    if (value == _alwaysIncludeSemantics)
      return;
    _alwaysIncludeSemantics = value;
    markNeedsSemanticsUpdate();
  }

  @override
  void attach(PipelineOwner owner) {
    super.attach(owner);
    opacity.addListener(_updateOpacity);
    _updateOpacity(); // in case it changed while we weren't listening
  }

  @override
  void detach() {
    opacity.removeListener(_updateOpacity);
    super.detach();
  }

  void _updateOpacity() {
    final int? oldAlpha = _alpha;
    _alpha = ui.Color.getAlphaFromOpacity(opacity.value);
    if (oldAlpha != _alpha) {
      final bool? didNeedCompositing = _currentlyNeedsCompositing;
      _currentlyNeedsCompositing = _alpha! > 0 && _alpha! < 255;
      if (child != null && didNeedCompositing != _currentlyNeedsCompositing)
        markNeedsCompositingBitsUpdate();
      markNeedsPaint();
      if (oldAlpha == 0 || _alpha == 0)
        markNeedsSemanticsUpdate();
    }
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      if (_alpha == 0) {
        // No need to keep the layer. We'll create a new one if necessary.
        layer = null;
        return;
      }
      if (_alpha == 255) {
        // No need to keep the layer. We'll create a new one if necessary.
        layer = null;
        context.paintChild(child!, offset);
        return;
      }
      assert(needsCompositing);
      layer = context.pushOpacity(offset, _alpha!, super.paint, oldLayer: layer as OpacityLayer?);
    }
  }

  @override
  void visitChildrenForSemantics(RenderObjectVisitor visitor) {
    if (child != null && (_alpha != 0 || alwaysIncludeSemantics))
      visitor(child!);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<Animation<double>>('opacity', opacity));
    properties.add(FlagProperty('alwaysIncludeSemantics', value: alwaysIncludeSemantics, ifTrue: 'alwaysIncludeSemantics'));
  }
}

/// Makes its child partially transparent, driven from an [Animation].
///
/// This is a variant of [RenderOpacity] that uses an [Animation<double>] rather
/// than a [double] to control the opacity.
class RenderAnimatedOpacity extends RenderProxyBox with RenderProxyBoxMixin, RenderAnimatedOpacityMixin<RenderBox> {
  /// Creates a partially transparent render object.
  ///
  /// The [opacity] argument must not be null.
  RenderAnimatedOpacity({
    required Animation<double> opacity,
    bool alwaysIncludeSemantics = false,
    RenderBox? child,
  }) : assert(opacity != null),
       assert(alwaysIncludeSemantics != null),
       super(child) {
    this.opacity = opacity;
    this.alwaysIncludeSemantics = alwaysIncludeSemantics;
  }
}

/// Signature for a function that creates a [Shader] for a given [Rect].
///
/// Used by [RenderShaderMask] and the [ShaderMask] widget.
typedef ShaderCallback = Shader Function(Rect bounds);

/// Applies a mask generated by a [Shader] to its child.
///
/// For example, [RenderShaderMask] can be used to gradually fade out the edge
/// of a child by using a [new ui.Gradient.linear] mask.
class RenderShaderMask extends RenderProxyBox {
  /// Creates a render object that applies a mask generated by a [Shader] to its child.
  ///
  /// The [shaderCallback] and [blendMode] arguments must not be null.
  RenderShaderMask({
    RenderBox? child,
    required ShaderCallback shaderCallback,
    BlendMode blendMode = BlendMode.modulate,
  }) : assert(shaderCallback != null),
       assert(blendMode != null),
       _shaderCallback = shaderCallback,
       _blendMode = blendMode,
       super(child);

  @override
  ShaderMaskLayer? get layer => super.layer as ShaderMaskLayer?;

  /// Called to creates the [Shader] that generates the mask.
  ///
  /// The shader callback is called with the current size of the child so that
  /// it can customize the shader to the size and location of the child.
  ///
  /// The rectangle will always be at the origin when called by
  /// [RenderShaderMask].
  // TODO(abarth): Use the delegate pattern here to avoid generating spurious
  // repaints when the ShaderCallback changes identity.
  ShaderCallback get shaderCallback => _shaderCallback;
  ShaderCallback _shaderCallback;
  set shaderCallback(ShaderCallback value) {
    assert(value != null);
    if (_shaderCallback == value)
      return;
    _shaderCallback = value;
    markNeedsPaint();
  }

  /// The [BlendMode] to use when applying the shader to the child.
  ///
  /// The default, [BlendMode.modulate], is useful for applying an alpha blend
  /// to the child. Other blend modes can be used to create other effects.
  BlendMode get blendMode => _blendMode;
  BlendMode _blendMode;
  set blendMode(BlendMode value) {
    assert(value != null);
    if (_blendMode == value)
      return;
    _blendMode = value;
    markNeedsPaint();
  }

  @override
  bool get alwaysNeedsCompositing => child != null;

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      assert(needsCompositing);
      layer ??= ShaderMaskLayer();
      layer!
        ..shader = _shaderCallback(Offset.zero & size)
        ..maskRect = offset & size
        ..blendMode = _blendMode;
      context.pushLayer(layer!, super.paint, offset);
    } else {
      layer = null;
    }
  }
}

/// Applies a filter to the existing painted content and then paints [child].
///
/// This effect is relatively expensive, especially if the filter is non-local,
/// such as a blur.
class RenderBackdropFilter extends RenderProxyBox {
  /// Creates a backdrop filter.
  ///
  /// The [filter] argument must not be null.
  RenderBackdropFilter({ RenderBox? child, required ui.ImageFilter filter })
    : assert(filter != null),
      _filter = filter,
      super(child);

  @override
  BackdropFilterLayer? get layer => super.layer as BackdropFilterLayer?;

  /// The image filter to apply to the existing painted content before painting
  /// the child.
  ///
  /// For example, consider using [new ui.ImageFilter.blur] to create a backdrop
  /// blur effect.
  ui.ImageFilter get filter => _filter;
  ui.ImageFilter _filter;
  set filter(ui.ImageFilter value) {
    assert(value != null);
    if (_filter == value)
      return;
    _filter = value;
    markNeedsPaint();
  }

  @override
  bool get alwaysNeedsCompositing => child != null;

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      assert(needsCompositing);
      layer ??= BackdropFilterLayer();
      layer!.filter = _filter;
      context.pushLayer(layer!, super.paint, offset);
    } else {
      layer = null;
    }
  }
}

/// An interface for providing custom clips.
///
/// This class is used by a number of clip widgets (e.g., [ClipRect] and
/// [ClipPath]).
///
/// The [getClip] method is called whenever the custom clip needs to be updated.
///
/// The [shouldReclip] method is called when a new instance of the class
/// is provided, to check if the new instance actually represents different
/// information.
///
/// The most efficient way to update the clip provided by this class is to
/// supply a `reclip` argument to the constructor of the [CustomClipper]. The
/// custom object will listen to this animation and update the clip whenever the
/// animation ticks, avoiding both the build and layout phases of the pipeline.
///
/// See also:
///
///  * [ClipRect], which can be customized with a [CustomClipper<Rect>].
///  * [ClipRRect], which can be customized with a [CustomClipper<RRect>].
///  * [ClipOval], which can be customized with a [CustomClipper<Rect>].
///  * [ClipPath], which can be customized with a [CustomClipper<Path>].
///  * [ShapeBorderClipper], for specifying a clip path using a [ShapeBorder].
abstract class CustomClipper<T> extends Listenable {
  /// Creates a custom clipper.
  ///
  /// The clipper will update its clip whenever [reclip] notifies its listeners.
  const CustomClipper({ Listenable? reclip }) : _reclip = reclip;

  final Listenable? _reclip;

  /// Register a closure to be notified when it is time to reclip.
  ///
  /// The [CustomClipper] implementation merely forwards to the same method on
  /// the [Listenable] provided to the constructor in the `reclip` argument, if
  /// it was not null.
  @override
  void addListener(VoidCallback listener) => _reclip?.addListener(listener);

  /// Remove a previously registered closure from the list of closures that the
  /// object notifies when it is time to reclip.
  ///
  /// The [CustomClipper] implementation merely forwards to the same method on
  /// the [Listenable] provided to the constructor in the `reclip` argument, if
  /// it was not null.
  @override
  void removeListener(VoidCallback listener) => _reclip?.removeListener(listener);

  /// Returns a description of the clip given that the render object being
  /// clipped is of the given size.
  T getClip(Size size);

  /// Returns an approximation of the clip returned by [getClip], as
  /// an axis-aligned Rect. This is used by the semantics layer to
  /// determine whether widgets should be excluded.
  ///
  /// By default, this returns a rectangle that is the same size as
  /// the RenderObject. If getClip returns a shape that is roughly the
  /// same size as the RenderObject (e.g. it's a rounded rectangle
  /// with very small arcs in the corners), then this may be adequate.
  Rect getApproximateClipRect(Size size) => Offset.zero & size;

  /// Called whenever a new instance of the custom clipper delegate class is
  /// provided to the clip object, or any time that a new clip object is created
  /// with a new instance of the custom clipper delegate class (which amounts to
  /// the same thing, because the latter is implemented in terms of the former).
  ///
  /// If the new instance represents different information than the old
  /// instance, then the method should return true, otherwise it should return
  /// false.
  ///
  /// If the method returns false, then the [getClip] call might be optimized
  /// away.
  ///
  /// It's possible that the [getClip] method will get called even if
  /// [shouldReclip] returns false or if the [shouldReclip] method is never
  /// called at all (e.g. if the box changes size).
  bool shouldReclip(covariant CustomClipper<T> oldClipper);

  @override
  String toString() => objectRuntimeType(this, 'CustomClipper');
}

/// A [CustomClipper] that clips to the outer path of a [ShapeBorder].
class ShapeBorderClipper extends CustomClipper<Path> {
  /// Creates a [ShapeBorder] clipper.
  ///
  /// The [shape] argument must not be null.
  ///
  /// The [textDirection] argument must be provided non-null if [shape]
  /// has a text direction dependency (for example if it is expressed in terms
  /// of "start" and "end" instead of "left" and "right"). It may be null if
  /// the border will not need the text direction to paint itself.
  const ShapeBorderClipper({
    required this.shape,
    this.textDirection,
  }) : assert(shape != null);

  /// The shape border whose outer path this clipper clips to.
  final ShapeBorder shape;

  /// The text direction to use for getting the outer path for [shape].
  ///
  /// [ShapeBorder]s can depend on the text direction (e.g having a "dent"
  /// towards the start of the shape).
  final TextDirection? textDirection;

  /// Returns the outer path of [shape] as the clip.
  @override
  Path getClip(Size size) {
    return shape.getOuterPath(Offset.zero & size, textDirection: textDirection);
  }

  @override
  bool shouldReclip(CustomClipper<Path> oldClipper) {
    if (oldClipper.runtimeType != ShapeBorderClipper)
      return true;
    final ShapeBorderClipper typedOldClipper = oldClipper as ShapeBorderClipper;
    return typedOldClipper.shape != shape
        || typedOldClipper.textDirection != textDirection;
  }
}

abstract class _RenderCustomClip<T> extends RenderProxyBox {
  _RenderCustomClip({
    RenderBox? child,
    CustomClipper<T>? clipper,
    Clip clipBehavior = Clip.antiAlias,
  }) : assert(clipBehavior != null),
       _clipper = clipper,
       _clipBehavior = clipBehavior,
       super(child);

  /// If non-null, determines which clip to use on the child.
  CustomClipper<T>? get clipper => _clipper;
  CustomClipper<T>? _clipper;
  set clipper(CustomClipper<T>? newClipper) {
    if (_clipper == newClipper)
      return;
    final CustomClipper<T>? oldClipper = _clipper;
    _clipper = newClipper;
    assert(newClipper != null || oldClipper != null);
    if (newClipper == null || oldClipper == null ||
        newClipper.runtimeType != oldClipper.runtimeType ||
        newClipper.shouldReclip(oldClipper)) {
      _markNeedsClip();
    }
    if (attached) {
      oldClipper?.removeListener(_markNeedsClip);
      newClipper?.addListener(_markNeedsClip);
    }
  }

  @override
  void attach(PipelineOwner owner) {
    super.attach(owner);
    _clipper?.addListener(_markNeedsClip);
  }

  @override
  void detach() {
    _clipper?.removeListener(_markNeedsClip);
    super.detach();
  }

  void _markNeedsClip() {
    _clip = null;
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  T get _defaultClip;
  T? _clip;

  Clip get clipBehavior => _clipBehavior;
  set clipBehavior(Clip value) {
    if (value != _clipBehavior) {
      _clipBehavior = value;
      markNeedsPaint();
    }
  }
  Clip _clipBehavior;

  @override
  void performLayout() {
    final Size? oldSize = hasSize ? size : null;
    super.performLayout();
    if (oldSize != size)
      _clip = null;
  }

  void _updateClip() {
    _clip ??= _clipper?.getClip(size) ?? _defaultClip;
  }

  @override
  Rect describeApproximatePaintClip(RenderObject child) {
    return _clipper?.getApproximateClipRect(size) ?? Offset.zero & size;
  }

  Paint? _debugPaint;
  TextPainter? _debugText;
  @override
  void debugPaintSize(PaintingContext context, Offset offset) {
    assert(() {
      _debugPaint ??= Paint()
        ..shader = ui.Gradient.linear(
          Offset.zero,
          const Offset(10.0, 10.0),
          <Color>[const Color(0x00000000), const Color(0xFFFF00FF), const Color(0xFFFF00FF), const Color(0x00000000)],
          <double>[0.25, 0.25, 0.75, 0.75],
          TileMode.repeated,
        )
        ..strokeWidth = 2.0
        ..style = PaintingStyle.stroke;
      _debugText ??= TextPainter(
        text: const TextSpan(
          text: '✂',
          style: TextStyle(
            color: Color(0xFFFF00FF),
              fontSize: 14.0,
            ),
          ),
          textDirection: TextDirection.rtl, // doesn't matter, it's one character
        )
        ..layout();
      return true;
    }());
  }
}

/// Clips its child using a rectangle.
///
/// By default, [RenderClipRect] prevents its child from painting outside its
/// bounds, but the size and location of the clip rect can be customized using a
/// custom [clipper].
class RenderClipRect extends _RenderCustomClip<Rect> {
  /// Creates a rectangular clip.
  ///
  /// If [clipper] is null, the clip will match the layout size and position of
  /// the child.
  ///
  /// The [clipBehavior] must not be null or [Clip.none].
  RenderClipRect({
    RenderBox? child,
    CustomClipper<Rect>? clipper,
    Clip clipBehavior = Clip.antiAlias,
  }) : assert(clipBehavior != null),
       assert(clipBehavior != Clip.none),
       super(child: child, clipper: clipper, clipBehavior: clipBehavior);

  @override
  Rect get _defaultClip => Offset.zero & size;

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    if (_clipper != null) {
      _updateClip();
      assert(_clip != null);
      if (!_clip!.contains(position))
        return false;
    }
    return super.hitTest(result, position: position);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      _updateClip();
      layer = context.pushClipRect(
        needsCompositing,
        offset,
        _clip!,
        super.paint,
        clipBehavior: clipBehavior,
        oldLayer: layer as ClipRectLayer?,
      );
    } else {
      layer = null;
    }
  }

  @override
  void debugPaintSize(PaintingContext context, Offset offset) {
    assert(() {
      if (child != null) {
        super.debugPaintSize(context, offset);
        context.canvas.drawRect(_clip!.shift(offset), _debugPaint!);
        _debugText!.paint(context.canvas, offset + Offset(_clip!.width / 8.0, -_debugText!.text!.style!.fontSize! * 1.1));
      }
      return true;
    }());
  }
}

/// Clips its child using a rounded rectangle.
///
/// By default, [RenderClipRRect] uses its own bounds as the base rectangle for
/// the clip, but the size and location of the clip can be customized using a
/// custom [clipper].
class RenderClipRRect extends _RenderCustomClip<RRect> {
  /// Creates a rounded-rectangular clip.
  ///
  /// The [borderRadius] defaults to [BorderRadius.zero], i.e. a rectangle with
  /// right-angled corners.
  ///
  /// If [clipper] is non-null, then [borderRadius] is ignored.
  ///
  /// The [clipBehavior] argument must not be null or [Clip.none].
  RenderClipRRect({
    RenderBox? child,
    BorderRadius borderRadius = BorderRadius.zero,
    CustomClipper<RRect>? clipper,
    Clip clipBehavior = Clip.antiAlias,
  }) : assert(clipBehavior != null),
       assert(clipBehavior != Clip.none),
       _borderRadius = borderRadius,
       super(child: child, clipper: clipper, clipBehavior: clipBehavior) {
    // `_borderRadius` has a non-nullable return type, but might be null when
    // running with weak checking, so we need to null check it anyway (and
    // ignore the warning that the null-handling logic is dead code).
    assert(_borderRadius != null || clipper != null);// ignore: dead_code
  }

  /// The border radius of the rounded corners.
  ///
  /// Values are clamped so that horizontal and vertical radii sums do not
  /// exceed width/height.
  ///
  /// This value is ignored if [clipper] is non-null.
  BorderRadius get borderRadius => _borderRadius;
  BorderRadius _borderRadius;
  set borderRadius(BorderRadius value) {
    assert(value != null);
    if (_borderRadius == value)
      return;
    _borderRadius = value;
    _markNeedsClip();
  }

  @override
  RRect get _defaultClip => _borderRadius.toRRect(Offset.zero & size);

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    if (_clipper != null) {
      _updateClip();
      assert(_clip != null);
      if (!_clip!.contains(position))
        return false;
    }
    return super.hitTest(result, position: position);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      _updateClip();
      layer = context.pushClipRRect(
        needsCompositing,
        offset,
        _clip!.outerRect,
        _clip!,
        super.paint, clipBehavior: clipBehavior, oldLayer: layer as ClipRRectLayer?,
      );
    } else {
      layer = null;
    }
  }

  @override
  void debugPaintSize(PaintingContext context, Offset offset) {
    assert(() {
      if (child != null) {
        super.debugPaintSize(context, offset);
        context.canvas.drawRRect(_clip!.shift(offset), _debugPaint!);
        _debugText!.paint(context.canvas, offset + Offset(_clip!.tlRadiusX, -_debugText!.text!.style!.fontSize! * 1.1));
      }
      return true;
    }());
  }
}

/// Clips its child using an oval.
///
/// By default, inscribes an axis-aligned oval into its layout dimensions and
/// prevents its child from painting outside that oval, but the size and
/// location of the clip oval can be customized using a custom [clipper].
class RenderClipOval extends _RenderCustomClip<Rect> {
  /// Creates an oval-shaped clip.
  ///
  /// If [clipper] is null, the oval will be inscribed into the layout size and
  /// position of the child.
  ///
  /// The [clipBehavior] argument must not be null or [Clip.none].
  RenderClipOval({
    RenderBox? child,
    CustomClipper<Rect>? clipper,
    Clip clipBehavior = Clip.antiAlias,
  }) : assert(clipBehavior != null),
       assert(clipBehavior != Clip.none),
       super(child: child, clipper: clipper, clipBehavior: clipBehavior);

  Rect? _cachedRect;
  late Path _cachedPath;

  Path _getClipPath(Rect rect) {
    if (rect != _cachedRect) {
      _cachedRect = rect;
      _cachedPath = Path()..addOval(_cachedRect!);
    }
    return _cachedPath;
  }

  @override
  Rect get _defaultClip => Offset.zero & size;

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    _updateClip();
    assert(_clip != null);
    final Offset center = _clip!.center;
    // convert the position to an offset from the center of the unit circle
    final Offset offset = Offset((position.dx - center.dx) / _clip!.width,
                                     (position.dy - center.dy) / _clip!.height);
    // check if the point is outside the unit circle
    if (offset.distanceSquared > 0.25) // x^2 + y^2 > r^2
      return false;
    return super.hitTest(result, position: position);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      _updateClip();
      layer = context.pushClipPath(
        needsCompositing,
        offset,
        _clip!,
        _getClipPath(_clip!),
        super.paint,
        clipBehavior: clipBehavior,
        oldLayer: layer as ClipPathLayer?,
      );
    } else {
      layer = null;
    }
  }

  @override
  void debugPaintSize(PaintingContext context, Offset offset) {
    assert(() {
      if (child != null) {
        super.debugPaintSize(context, offset);
        context.canvas.drawPath(_getClipPath(_clip!).shift(offset), _debugPaint!);
        _debugText!.paint(context.canvas, offset + Offset((_clip!.width - _debugText!.width) / 2.0, -_debugText!.text!.style!.fontSize! * 1.1));
      }
      return true;
    }());
  }
}

/// Clips its child using a path.
///
/// Takes a delegate whose primary method returns a path that should
/// be used to prevent the child from painting outside the path.
///
/// Clipping to a path is expensive. Certain shapes have more
/// optimized render objects:
///
///  * To clip to a rectangle, consider [RenderClipRect].
///  * To clip to an oval or circle, consider [RenderClipOval].
///  * To clip to a rounded rectangle, consider [RenderClipRRect].
class RenderClipPath extends _RenderCustomClip<Path> {
  /// Creates a path clip.
  ///
  /// If [clipper] is null, the clip will be a rectangle that matches the layout
  /// size and location of the child. However, rather than use this default,
  /// consider using a [RenderClipRect], which can achieve the same effect more
  /// efficiently.
  ///
  /// The [clipBehavior] argument must not be null or [Clip.none].
  RenderClipPath({
    RenderBox? child,
    CustomClipper<Path>? clipper,
    Clip clipBehavior = Clip.antiAlias,
  }) : assert(clipBehavior != null),
       assert(clipBehavior != Clip.none),
       super(child: child, clipper: clipper, clipBehavior: clipBehavior);

  @override
  Path get _defaultClip => Path()..addRect(Offset.zero & size);

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    if (_clipper != null) {
      _updateClip();
      assert(_clip != null);
      if (!_clip!.contains(position))
        return false;
    }
    return super.hitTest(result, position: position);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      _updateClip();
      layer = context.pushClipPath(
        needsCompositing,
        offset,
        Offset.zero & size,
        _clip!,
        super.paint,
        clipBehavior: clipBehavior,
        oldLayer: layer as ClipPathLayer?,
      );
    } else {
      layer = null;
    }
  }

  @override
  void debugPaintSize(PaintingContext context, Offset offset) {
    assert(() {
      if (child != null) {
        super.debugPaintSize(context, offset);
        context.canvas.drawPath(_clip!.shift(offset), _debugPaint!);
        _debugText!.paint(context.canvas, offset);
      }
      return true;
    }());
  }
}

/// A physical model layer casts a shadow based on its [elevation].
///
/// The concrete implementations [RenderPhysicalModel] and [RenderPhysicalShape]
/// determine the actual shape of the physical model.
abstract class _RenderPhysicalModelBase<T> extends _RenderCustomClip<T> {
  /// The [shape], [elevation], [color], and [shadowColor] must not be null.
  /// Additionally, the [elevation] must be non-negative.
  _RenderPhysicalModelBase({
    required RenderBox? child,
    required double elevation,
    required Color color,
    required Color shadowColor,
    Clip clipBehavior = Clip.none,
    CustomClipper<T>? clipper,
  }) : assert(elevation != null && elevation >= 0.0),
       assert(color != null),
       assert(shadowColor != null),
       assert(clipBehavior != null),
       _elevation = elevation,
       _color = color,
       _shadowColor = shadowColor,
       super(child: child, clipBehavior: clipBehavior, clipper: clipper);

  /// The z-coordinate relative to the parent at which to place this material.
  ///
  /// The value is non-negative.
  ///
  /// If [debugDisableShadows] is set, this value is ignored and no shadow is
  /// drawn (an outline is rendered instead).
  double get elevation => _elevation;
  double _elevation;
  set elevation(double value) {
    assert(value != null && value >= 0.0);
    if (elevation == value)
      return;
    final bool didNeedCompositing = alwaysNeedsCompositing;
    _elevation = value;
    if (didNeedCompositing != alwaysNeedsCompositing)
      markNeedsCompositingBitsUpdate();
    markNeedsPaint();
  }

  /// The shadow color.
  Color get shadowColor => _shadowColor;
  Color _shadowColor;
  set shadowColor(Color value) {
    assert(value != null);
    if (shadowColor == value)
      return;
    _shadowColor = value;
    markNeedsPaint();
  }

  /// The background color.
  Color get color => _color;
  Color _color;
  set color(Color value) {
    assert(value != null);
    if (color == value)
      return;
    _color = value;
    markNeedsPaint();
  }

  @override
  bool get alwaysNeedsCompositing => true;

  @override
  void describeSemanticsConfiguration(SemanticsConfiguration config) {
    super.describeSemanticsConfiguration(config);
    config.elevation = elevation;
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder description) {
    super.debugFillProperties(description);
    description.add(DoubleProperty('elevation', elevation));
    description.add(ColorProperty('color', color));
    description.add(ColorProperty('shadowColor', color));
  }
}

/// Creates a physical model layer that clips its child to a rounded
/// rectangle.
///
/// A physical model layer casts a shadow based on its [elevation].
class RenderPhysicalModel extends _RenderPhysicalModelBase<RRect> {
  /// Creates a rounded-rectangular clip.
  ///
  /// The [color] is required.
  ///
  /// The [shape], [elevation], [color], [clipBehavior], and [shadowColor]
  /// arguments must not be null. Additionally, the [elevation] must be
  /// non-negative.
  RenderPhysicalModel({
    RenderBox? child,
    BoxShape shape = BoxShape.rectangle,
    Clip clipBehavior = Clip.none,
    BorderRadius? borderRadius,
    double elevation = 0.0,
    required Color color,
    Color shadowColor = const Color(0xFF000000),
  }) : assert(shape != null),
       assert(clipBehavior != null),
       assert(elevation != null && elevation >= 0.0),
       assert(color != null),
       assert(shadowColor != null),
       _shape = shape,
       _borderRadius = borderRadius,
       super(
         clipBehavior: clipBehavior,
         child: child,
         elevation: elevation,
         color: color,
         shadowColor: shadowColor,
       );

  @override
  PhysicalModelLayer? get layer => super.layer as PhysicalModelLayer?;

  /// The shape of the layer.
  ///
  /// Defaults to [BoxShape.rectangle]. The [borderRadius] affects the corners
  /// of the rectangle.
  BoxShape get shape => _shape;
  BoxShape _shape;
  set shape(BoxShape value) {
    assert(value != null);
    if (shape == value)
      return;
    _shape = value;
    _markNeedsClip();
  }

  /// The border radius of the rounded corners.
  ///
  /// Values are clamped so that horizontal and vertical radii sums do not
  /// exceed width/height.
  ///
  /// This property is ignored if the [shape] is not [BoxShape.rectangle].
  ///
  /// The value null is treated like [BorderRadius.zero].
  BorderRadius? get borderRadius => _borderRadius;
  BorderRadius? _borderRadius;
  set borderRadius(BorderRadius? value) {
    if (borderRadius == value)
      return;
    _borderRadius = value;
    _markNeedsClip();
  }

  @override
  RRect get _defaultClip {
    assert(hasSize);
    assert(_shape != null);
    switch (_shape) {
      case BoxShape.rectangle:
        return (borderRadius ?? BorderRadius.zero).toRRect(Offset.zero & size);
      case BoxShape.circle:
        final Rect rect = Offset.zero & size;
        return RRect.fromRectXY(rect, rect.width / 2, rect.height / 2);
    }
  }

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    if (_clipper != null) {
      _updateClip();
      assert(_clip != null);
      if (!_clip!.contains(position))
        return false;
    }
    return super.hitTest(result, position: position);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      _updateClip();
      final RRect offsetRRect = _clip!.shift(offset);
      final Rect offsetBounds = offsetRRect.outerRect;
      final Path offsetRRectAsPath = Path()..addRRect(offsetRRect);
      bool paintShadows = true;
      assert(() {
        if (debugDisableShadows) {
          if (elevation > 0.0) {
            context.canvas.drawRRect(
              offsetRRect,
              Paint()
                ..color = shadowColor
                ..style = PaintingStyle.stroke
                ..strokeWidth = elevation * 2.0,
            );
          }
          paintShadows = false;
        }
        return true;
      }());
      layer ??= PhysicalModelLayer();
      layer!
        ..clipPath = offsetRRectAsPath
        ..clipBehavior = clipBehavior
        ..elevation = paintShadows ? elevation : 0.0
        ..color = color
        ..shadowColor = shadowColor;
      context.pushLayer(layer!, super.paint, offset, childPaintBounds: offsetBounds);
      assert(() {
        layer!.debugCreator = debugCreator;
        return true;
      }());
    } else {
      layer = null;
    }
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder description) {
    super.debugFillProperties(description);
    description.add(DiagnosticsProperty<BoxShape>('shape', shape));
    description.add(DiagnosticsProperty<BorderRadius>('borderRadius', borderRadius));
  }
}

/// Creates a physical shape layer that clips its child to a [Path].
///
/// A physical shape layer casts a shadow based on its [elevation].
///
/// See also:
///
///  * [RenderPhysicalModel], which is optimized for rounded rectangles and
///    circles.
class RenderPhysicalShape extends _RenderPhysicalModelBase<Path> {
  /// Creates an arbitrary shape clip.
  ///
  /// The [color] and [clipper] parameters are required.
  ///
  /// The [clipper], [elevation], [color] and [shadowColor] must not be null.
  /// Additionally, the [elevation] must be non-negative.
  RenderPhysicalShape({
    RenderBox? child,
    required CustomClipper<Path> clipper,
    Clip clipBehavior = Clip.none,
    double elevation = 0.0,
    required Color color,
    Color shadowColor = const Color(0xFF000000),
  }) : assert(clipper != null),
       assert(elevation != null && elevation >= 0.0),
       assert(color != null),
       assert(shadowColor != null),
       super(
         child: child,
         elevation: elevation,
         color: color,
         shadowColor: shadowColor,
         clipper: clipper,
         clipBehavior: clipBehavior,
       );

  @override
  PhysicalModelLayer? get layer => super.layer as PhysicalModelLayer?;

  @override
  Path get _defaultClip => Path()..addRect(Offset.zero & size);

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    if (_clipper != null) {
      _updateClip();
      assert(_clip != null);
      if (!_clip!.contains(position))
        return false;
    }
    return super.hitTest(result, position: position);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      _updateClip();
      final Rect offsetBounds = offset & size;
      final Path offsetPath = _clip!.shift(offset);
      bool paintShadows = true;
      assert(() {
        if (debugDisableShadows) {
          if (elevation > 0.0) {
            context.canvas.drawPath(
              offsetPath,
              Paint()
                ..color = shadowColor
                ..style = PaintingStyle.stroke
                ..strokeWidth = elevation * 2.0,
            );
          }
          paintShadows = false;
        }
        return true;
      }());
      layer ??= PhysicalModelLayer();
      layer!
        ..clipPath = offsetPath
        ..clipBehavior = clipBehavior
        ..elevation = paintShadows ? elevation : 0.0
        ..color = color
        ..shadowColor = shadowColor;
      context.pushLayer(layer!, super.paint, offset, childPaintBounds: offsetBounds);
      assert(() {
        layer!.debugCreator = debugCreator;
        return true;
      }());
    } else {
      layer = null;
    }
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder description) {
    super.debugFillProperties(description);
    description.add(DiagnosticsProperty<CustomClipper<Path>>('clipper', clipper));
  }
}

/// Where to paint a box decoration.
enum DecorationPosition {
  /// Paint the box decoration behind the children.
  background,

  /// Paint the box decoration in front of the children.
  foreground,
}

/// Paints a [Decoration] either before or after its child paints.
class RenderDecoratedBox extends RenderProxyBox {
  /// Creates a decorated box.
  ///
  /// The [decoration], [position], and [configuration] arguments must not be
  /// null. By default the decoration paints behind the child.
  ///
  /// The [ImageConfiguration] will be passed to the decoration (with the size
  /// filled in) to let it resolve images.
  RenderDecoratedBox({
    required Decoration decoration,
    DecorationPosition position = DecorationPosition.background,
    ImageConfiguration configuration = ImageConfiguration.empty,
    RenderBox? child,
  }) : assert(decoration != null),
       assert(position != null),
       assert(configuration != null),
       _decoration = decoration,
       _position = position,
       _configuration = configuration,
       super(child);

  BoxPainter? _painter;

  /// What decoration to paint.
  ///
  /// Commonly a [BoxDecoration].
  Decoration get decoration => _decoration;
  Decoration _decoration;
  set decoration(Decoration value) {
    assert(value != null);
    if (value == _decoration)
      return;
    _painter?.dispose();
    _painter = null;
    _decoration = value;
    markNeedsPaint();
  }

  /// Whether to paint the box decoration behind or in front of the child.
  DecorationPosition get position => _position;
  DecorationPosition _position;
  set position(DecorationPosition value) {
    assert(value != null);
    if (value == _position)
      return;
    _position = value;
    markNeedsPaint();
  }

  /// The settings to pass to the decoration when painting, so that it can
  /// resolve images appropriately. See [ImageProvider.resolve] and
  /// [BoxPainter.paint].
  ///
  /// The [ImageConfiguration.textDirection] field is also used by
  /// direction-sensitive [Decoration]s for painting and hit-testing.
  ImageConfiguration get configuration => _configuration;
  ImageConfiguration _configuration;
  set configuration(ImageConfiguration value) {
    assert(value != null);
    if (value == _configuration)
      return;
    _configuration = value;
    markNeedsPaint();
  }

  @override
  void detach() {
    _painter?.dispose();
    _painter = null;
    super.detach();
    // Since we're disposing of our painter, we won't receive change
    // notifications. We mark ourselves as needing paint so that we will
    // resubscribe to change notifications. If we didn't do this, then, for
    // example, animated GIFs would stop animating when a DecoratedBox gets
    // moved around the tree due to GlobalKey reparenting.
    markNeedsPaint();
  }

  @override
  bool hitTestSelf(Offset position) {
    return _decoration.hitTest(size, position, textDirection: configuration.textDirection);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    assert(size.width != null);
    assert(size.height != null);
    _painter ??= _decoration.createBoxPainter(markNeedsPaint);
    final ImageConfiguration filledConfiguration = configuration.copyWith(size: size);
    if (position == DecorationPosition.background) {
      int? debugSaveCount;
      assert(() {
        debugSaveCount = context.canvas.getSaveCount();
        return true;
      }());
      _painter!.paint(context.canvas, offset, filledConfiguration);
      assert(() {
        if (debugSaveCount != context.canvas.getSaveCount()) {
          throw FlutterError.fromParts(<DiagnosticsNode>[
            ErrorSummary('${_decoration.runtimeType} painter had mismatching save and restore calls.'),
            ErrorDescription(
              'Before painting the decoration, the canvas save count was $debugSaveCount. '
              'After painting it, the canvas save count was ${context.canvas.getSaveCount()}. '
              'Every call to save() or saveLayer() must be matched by a call to restore().'
            ),
            DiagnosticsProperty<Decoration>('The decoration was', decoration, style: DiagnosticsTreeStyle.errorProperty),
            DiagnosticsProperty<BoxPainter>('The painter was', _painter, style: DiagnosticsTreeStyle.errorProperty),
          ]);
        }
        return true;
      }());
      if (decoration.isComplex)
        context.setIsComplexHint();
    }
    super.paint(context, offset);
    if (position == DecorationPosition.foreground) {
      _painter!.paint(context.canvas, offset, filledConfiguration);
      if (decoration.isComplex)
        context.setIsComplexHint();
    }
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(_decoration.toDiagnosticsNode(name: 'decoration'));
    properties.add(DiagnosticsProperty<ImageConfiguration>('configuration', configuration));
  }
}

/// Applies a transformation before painting its child.
class RenderTransform extends RenderProxyBox {
  /// Creates a render object that transforms its child.
  ///
  /// The [transform] argument must not be null.
  RenderTransform({
    required Matrix4 transform,
    Offset? origin,
    AlignmentGeometry? alignment,
    TextDirection? textDirection,
    this.transformHitTests = true,
    RenderBox? child,
  }) : assert(transform != null),
       super(child) {
    this.transform = transform;
    this.alignment = alignment;
    this.textDirection = textDirection;
    this.origin = origin;
  }

  /// The origin of the coordinate system (relative to the upper left corner of
  /// this render object) in which to apply the matrix.
  ///
  /// Setting an origin is equivalent to conjugating the transform matrix by a
  /// translation. This property is provided just for convenience.
  Offset? get origin => _origin;
  Offset? _origin;
  set origin(Offset? value) {
    if (_origin == value)
      return;
    _origin = value;
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// The alignment of the origin, relative to the size of the box.
  ///
  /// This is equivalent to setting an origin based on the size of the box.
  /// If it is specified at the same time as an offset, both are applied.
  ///
  /// An [AlignmentDirectional.centerStart] value is the same as an [Alignment]
  /// whose [Alignment.x] value is `-1.0` if [textDirection] is
  /// [TextDirection.ltr], and `1.0` if [textDirection] is [TextDirection.rtl].
  /// Similarly [AlignmentDirectional.centerEnd] is the same as an [Alignment]
  /// whose [Alignment.x] value is `1.0` if [textDirection] is
  /// [TextDirection.ltr], and `-1.0` if [textDirection] is [TextDirection.rtl].
  AlignmentGeometry? get alignment => _alignment;
  AlignmentGeometry? _alignment;
  set alignment(AlignmentGeometry? value) {
    if (_alignment == value)
      return;
    _alignment = value;
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// The text direction with which to resolve [alignment].
  ///
  /// This may be changed to null, but only after [alignment] has been changed
  /// to a value that does not depend on the direction.
  TextDirection? get textDirection => _textDirection;
  TextDirection? _textDirection;
  set textDirection(TextDirection? value) {
    if (_textDirection == value)
      return;
    _textDirection = value;
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// When set to true, hit tests are performed based on the position of the
  /// child as it is painted. When set to false, hit tests are performed
  /// ignoring the transformation.
  ///
  /// [applyPaintTransform], and therefore [localToGlobal] and [globalToLocal],
  /// always honor the transformation, regardless of the value of this property.
  bool transformHitTests;

  // Note the lack of a getter for transform because Matrix4 is not immutable
  Matrix4? _transform;

  /// The matrix to transform the child by during painting.
  set transform(Matrix4 value) {
    assert(value != null);
    if (_transform == value)
      return;
    _transform = Matrix4.copy(value);
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// Sets the transform to the identity matrix.
  void setIdentity() {
    _transform!.setIdentity();
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// Concatenates a rotation about the x axis into the transform.
  void rotateX(double radians) {
    _transform!.rotateX(radians);
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// Concatenates a rotation about the y axis into the transform.
  void rotateY(double radians) {
    _transform!.rotateY(radians);
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// Concatenates a rotation about the z axis into the transform.
  void rotateZ(double radians) {
    _transform!.rotateZ(radians);
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// Concatenates a translation by (x, y, z) into the transform.
  void translate(double x, [ double y = 0.0, double z = 0.0 ]) {
    _transform!.translate(x, y, z);
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  /// Concatenates a scale into the transform.
  void scale(double x, [ double? y, double? z ]) {
    _transform!.scale(x, y, z);
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  Matrix4? get _effectiveTransform {
    final Alignment? resolvedAlignment = alignment?.resolve(textDirection);
    if (_origin == null && resolvedAlignment == null)
      return _transform;
    final Matrix4 result = Matrix4.identity();
    if (_origin != null)
      result.translate(_origin!.dx, _origin!.dy);
    Offset? translation;
    if (resolvedAlignment != null) {
      translation = resolvedAlignment.alongSize(size);
      result.translate(translation.dx, translation.dy);
    }
    result.multiply(_transform!);
    if (resolvedAlignment != null)
      result.translate(-translation!.dx, -translation.dy);
    if (_origin != null)
      result.translate(-_origin!.dx, -_origin!.dy);
    return result;
  }

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    // RenderTransform objects don't check if they are
    // themselves hit, because it's confusing to think about
    // how the untransformed size and the child's transformed
    // position interact.
    return hitTestChildren(result, position: position);
  }

  @override
  bool hitTestChildren(BoxHitTestResult result, { required Offset position }) {
    assert(!transformHitTests || _effectiveTransform != null);
    return result.addWithPaintTransform(
      transform: transformHitTests ? _effectiveTransform : null,
      position: position,
      hitTest: (BoxHitTestResult result, Offset? position) {
        return super.hitTestChildren(result, position: position!);
      },
    );
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (child != null) {
      final Matrix4 transform = _effectiveTransform!;
      final Offset? childOffset = MatrixUtils.getAsTranslation(transform);
      if (childOffset == null) {
        layer = context.pushTransform(
          needsCompositing,
          offset,
          transform,
          super.paint,
          oldLayer: layer as TransformLayer?,
        );
      } else {
        super.paint(context, offset + childOffset);
        layer = null;
      }
    }
  }

  @override
  void applyPaintTransform(RenderBox child, Matrix4 transform) {
    transform.multiply(_effectiveTransform!);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(TransformProperty('transform matrix', _transform));
    properties.add(DiagnosticsProperty<Offset>('origin', origin));
    properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
    properties.add(EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
    properties.add(DiagnosticsProperty<bool>('transformHitTests', transformHitTests));
  }
}

/// Scales and positions its child within itself according to [fit].
class RenderFittedBox extends RenderProxyBox {
  /// Scales and positions its child within itself.
  ///
  /// The [fit] and [alignment] arguments must not be null.
  RenderFittedBox({
    BoxFit fit = BoxFit.contain,
    AlignmentGeometry alignment = Alignment.center,
    TextDirection? textDirection,
    RenderBox? child,
    Clip clipBehavior = Clip.none,
  }) : assert(fit != null),
       assert(alignment != null),
       assert(clipBehavior != null),
       _fit = fit,
       _alignment = alignment,
       _textDirection = textDirection,
       _clipBehavior = clipBehavior,
       super(child);

  Alignment? _resolvedAlignment;

  void _resolve() {
    if (_resolvedAlignment != null)
      return;
    _resolvedAlignment = alignment.resolve(textDirection);
  }

  void _markNeedResolution() {
    _resolvedAlignment = null;
    markNeedsPaint();
  }

  bool _fitAffectsLayout(BoxFit fit) {
    switch (fit) {
      case BoxFit.scaleDown:
        return true;
      default:
        return false;
    }
  }

  /// How to inscribe the child into the space allocated during layout.
  BoxFit get fit => _fit;
  BoxFit _fit;
  set fit(BoxFit value) {
    assert(value != null);
    if (_fit == value)
      return;
    final BoxFit lastFit = _fit;
    _fit = value;
    if (_fitAffectsLayout(lastFit) || _fitAffectsLayout(value)) {
      markNeedsLayout();
    } else {
      _clearPaintData();
      markNeedsPaint();
    }
  }

  /// How to align the child within its parent's bounds.
  ///
  /// An alignment of (0.0, 0.0) aligns the child to the top-left corner of its
  /// parent's bounds. An alignment of (1.0, 0.5) aligns the child to the middle
  /// of the right edge of its parent's bounds.
  ///
  /// If this is set to an [AlignmentDirectional] object, then
  /// [textDirection] must not be null.
  AlignmentGeometry get alignment => _alignment;
  AlignmentGeometry _alignment;
  set alignment(AlignmentGeometry value) {
    assert(value != null);
    if (_alignment == value)
      return;
    _alignment = value;
    _clearPaintData();
    _markNeedResolution();
  }

  /// The text direction with which to resolve [alignment].
  ///
  /// This may be changed to null, but only after [alignment] has been changed
  /// to a value that does not depend on the direction.
  TextDirection? get textDirection => _textDirection;
  TextDirection? _textDirection;
  set textDirection(TextDirection? value) {
    if (_textDirection == value)
      return;
    _textDirection = value;
    _clearPaintData();
    _markNeedResolution();
  }

  // TODO(ianh): The intrinsic dimensions of this box are wrong.

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    if (child != null) {
      final Size childSize = child!.getDryLayout(const BoxConstraints());

      // During [RenderObject.debugCheckingIntrinsics] a child that doesn't
      // support dry layout may provide us with an invalid size that triggers
      // assertions if we try to work with it. Instead of throwing, we bail
      // out early in that case.
      bool invalidChildSize = false;
      assert(() {
        if (RenderObject.debugCheckingIntrinsics && childSize.width * childSize.height == 0.0) {
          invalidChildSize = true;
        }
        return true;
      }());
      if (invalidChildSize) {
        assert(debugCannotComputeDryLayout(
          reason: 'Child provided invalid size of $childSize.',
        ));
        return Size.zero;
      }

      switch (fit) {
        case BoxFit.scaleDown:
          final BoxConstraints sizeConstraints = constraints.loosen();
          final Size unconstrainedSize = sizeConstraints.constrainSizeAndAttemptToPreserveAspectRatio(childSize);
          return constraints.constrain(unconstrainedSize);
        default:
          return constraints.constrainSizeAndAttemptToPreserveAspectRatio(childSize);
      }
    } else {
      return constraints.smallest;
    }
  }

  @override
  void performLayout() {
    if (child != null) {
      child!.layout(const BoxConstraints(), parentUsesSize: true);
      switch (fit) {
        case BoxFit.scaleDown:
          final BoxConstraints sizeConstraints = constraints.loosen();
          final Size unconstrainedSize = sizeConstraints.constrainSizeAndAttemptToPreserveAspectRatio(child!.size);
          size = constraints.constrain(unconstrainedSize);
          break;
        default:
          size = constraints.constrainSizeAndAttemptToPreserveAspectRatio(child!.size);
          break;
      }
      _clearPaintData();
    } else {
      size = constraints.smallest;
    }
  }

  bool? _hasVisualOverflow;
  Matrix4? _transform;

  /// {@macro flutter.material.Material.clipBehavior}
  ///
  /// Defaults to [Clip.none], and must not be null.
  Clip get clipBehavior => _clipBehavior;
  Clip _clipBehavior = Clip.none;
  set clipBehavior(Clip value) {
    assert(value != null);
    if (value != _clipBehavior) {
      _clipBehavior = value;
      markNeedsPaint();
      markNeedsSemanticsUpdate();
    }
  }

  void _clearPaintData() {
    _hasVisualOverflow = null;
    _transform = null;
  }

  void _updatePaintData() {
    if (_transform != null)
      return;

    if (child == null) {
      _hasVisualOverflow = false;
      _transform = Matrix4.identity();
    } else {
      _resolve();
      final Size childSize = child!.size;
      final FittedSizes sizes = applyBoxFit(_fit, childSize, size);
      final double scaleX = sizes.destination.width / sizes.source.width;
      final double scaleY = sizes.destination.height / sizes.source.height;
      final Rect sourceRect = _resolvedAlignment!.inscribe(sizes.source, Offset.zero & childSize);
      final Rect destinationRect = _resolvedAlignment!.inscribe(sizes.destination, Offset.zero & size);
      _hasVisualOverflow = sourceRect.width < childSize.width || sourceRect.height < childSize.height;
      assert(scaleX.isFinite && scaleY.isFinite);
      _transform = Matrix4.translationValues(destinationRect.left, destinationRect.top, 0.0)
        ..scale(scaleX, scaleY, 1.0)
        ..translate(-sourceRect.left, -sourceRect.top);
      assert(_transform!.storage.every((double value) => value.isFinite));
    }
  }

  TransformLayer? _paintChildWithTransform(PaintingContext context, Offset offset) {
    final Offset? childOffset = MatrixUtils.getAsTranslation(_transform!);
    if (childOffset == null)
      return context.pushTransform(needsCompositing, offset, _transform!, super.paint,
          oldLayer: layer is TransformLayer ? layer! as TransformLayer : null);
    else
      super.paint(context, offset + childOffset);
    return null;
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (size.isEmpty || child!.size.isEmpty)
      return;
    _updatePaintData();
    if (child != null) {
      if (_hasVisualOverflow! && clipBehavior != Clip.none)
        layer = context.pushClipRect(needsCompositing, offset, Offset.zero & size, _paintChildWithTransform,
            oldLayer: layer is ClipRectLayer ? layer! as ClipRectLayer : null, clipBehavior: clipBehavior);
      else
        layer = _paintChildWithTransform(context, offset);
    }
  }

  @override
  bool hitTestChildren(BoxHitTestResult result, { required Offset position }) {
    if (size.isEmpty || child?.size.isEmpty == true)
      return false;
    _updatePaintData();
    return result.addWithPaintTransform(
      transform: _transform,
      position: position,
      hitTest: (BoxHitTestResult result, Offset? position) {
        return super.hitTestChildren(result, position: position!);
      },
    );
  }

  @override
  void applyPaintTransform(RenderBox child, Matrix4 transform) {
    if (size.isEmpty || child.size.isEmpty) {
      transform.setZero();
    } else {
      _updatePaintData();
      transform.multiply(_transform!);
    }
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(EnumProperty<BoxFit>('fit', fit));
    properties.add(DiagnosticsProperty<AlignmentGeometry>('alignment', alignment));
    properties.add(EnumProperty<TextDirection>('textDirection', textDirection, defaultValue: null));
  }
}

/// Applies a translation transformation before painting its child.
///
/// The translation is expressed as an [Offset] scaled to the child's size. For
/// example, an [Offset] with a `dx` of 0.25 will result in a horizontal
/// translation of one quarter the width of the child.
///
/// Hit tests will only be detected inside the bounds of the
/// [RenderFractionalTranslation], even if the contents are offset such that
/// they overflow.
class RenderFractionalTranslation extends RenderProxyBox {
  /// Creates a render object that translates its child's painting.
  ///
  /// The [translation] argument must not be null.
  RenderFractionalTranslation({
    required Offset translation,
    this.transformHitTests = true,
    RenderBox? child,
  }) : assert(translation != null),
       _translation = translation,
       super(child);

  /// The translation to apply to the child, scaled to the child's size.
  ///
  /// For example, an [Offset] with a `dx` of 0.25 will result in a horizontal
  /// translation of one quarter the width of the child.
  Offset get translation => _translation;
  Offset _translation;
  set translation(Offset value) {
    assert(value != null);
    if (_translation == value)
      return;
    _translation = value;
    markNeedsPaint();
    markNeedsSemanticsUpdate();
  }

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    // RenderFractionalTranslation objects don't check if they are
    // themselves hit, because it's confusing to think about
    // how the untransformed size and the child's transformed
    // position interact.
    return hitTestChildren(result, position: position);
  }

  /// When set to true, hit tests are performed based on the position of the
  /// child as it is painted. When set to false, hit tests are performed
  /// ignoring the transformation.
  ///
  /// applyPaintTransform(), and therefore localToGlobal() and globalToLocal(),
  /// always honor the transformation, regardless of the value of this property.
  bool transformHitTests;

  @override
  bool hitTestChildren(BoxHitTestResult result, { required Offset position }) {
    assert(!debugNeedsLayout);
    return result.addWithPaintOffset(
      offset: transformHitTests
          ? Offset(translation.dx * size.width, translation.dy * size.height)
          : null,
      position: position,
      hitTest: (BoxHitTestResult result, Offset? position) {
        return super.hitTestChildren(result, position: position!);
      },
    );
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    assert(!debugNeedsLayout);
    if (child != null) {
      super.paint(context, Offset(
        offset.dx + translation.dx * size.width,
        offset.dy + translation.dy * size.height,
      ));
    }
  }

  @override
  void applyPaintTransform(RenderBox child, Matrix4 transform) {
    transform.translate(
      translation.dx * size.width,
      translation.dy * size.height,
    );
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<Offset>('translation', translation));
    properties.add(DiagnosticsProperty<bool>('transformHitTests', transformHitTests));
  }
}

/// Signature for listening to [PointerDownEvent] events.
///
/// Used by [Listener] and [RenderPointerListener].
typedef PointerDownEventListener = void Function(PointerDownEvent event);

/// Signature for listening to [PointerMoveEvent] events.
///
/// Used by [Listener] and [RenderPointerListener].
typedef PointerMoveEventListener = void Function(PointerMoveEvent event);

/// Signature for listening to [PointerUpEvent] events.
///
/// Used by [Listener] and [RenderPointerListener].
typedef PointerUpEventListener = void Function(PointerUpEvent event);

/// Signature for listening to [PointerCancelEvent] events.
///
/// Used by [Listener] and [RenderPointerListener].
typedef PointerCancelEventListener = void Function(PointerCancelEvent event);

/// Signature for listening to [PointerSignalEvent] events.
///
/// Used by [Listener] and [RenderPointerListener].
typedef PointerSignalEventListener = void Function(PointerSignalEvent event);

/// Calls callbacks in response to common pointer events.
///
/// It responds to events that can construct gestures, such as when the
/// pointer is pointer is pressed and moved, and then released or canceled.
///
/// It does not respond to events that are exclusive to mouse, such as when the
/// mouse enters and exits a region without pressing any buttons. For
/// these events, use [RenderMouseRegion].
///
/// If it has a child, defers to the child for sizing behavior.
///
/// If it does not have a child, grows to fit the parent-provided constraints.
class RenderPointerListener extends RenderProxyBoxWithHitTestBehavior {
  /// Creates a render object that forwards pointer events to callbacks.
  ///
  /// The [behavior] argument defaults to [HitTestBehavior.deferToChild].
  RenderPointerListener({
    this.onPointerDown,
    this.onPointerMove,
    this.onPointerUp,
    this.onPointerHover,
    this.onPointerCancel,
    this.onPointerSignal,
    HitTestBehavior behavior = HitTestBehavior.deferToChild,
    RenderBox? child,
  }) : super(behavior: behavior, child: child);

  /// Called when a pointer comes into contact with the screen (for touch
  /// pointers), or has its button pressed (for mouse pointers) at this widget's
  /// location.
  PointerDownEventListener? onPointerDown;

  /// Called when a pointer that triggered an [onPointerDown] changes position.
  PointerMoveEventListener? onPointerMove;

  /// Called when a pointer that triggered an [onPointerDown] is no longer in
  /// contact with the screen.
  PointerUpEventListener? onPointerUp;

  /// Called when a pointer that has not an [onPointerDown] changes position.
  PointerHoverEventListener? onPointerHover;

  /// Called when the input from a pointer that triggered an [onPointerDown] is
  /// no longer directed towards this receiver.
  PointerCancelEventListener? onPointerCancel;

  /// Called when a pointer signal occurs over this object.
  PointerSignalEventListener? onPointerSignal;

  @override
  Size computeSizeForNoChild(BoxConstraints constraints) {
    return constraints.biggest;
  }

  @override
  void handleEvent(PointerEvent event, HitTestEntry entry) {
    assert(debugHandleEvent(event, entry));
    if (event is PointerDownEvent)
      return onPointerDown?.call(event);
    if (event is PointerMoveEvent)
      return onPointerMove?.call(event);
    if (event is PointerUpEvent)
      return onPointerUp?.call(event);
    if (event is PointerHoverEvent)
      return onPointerHover?.call(event);
    if (event is PointerCancelEvent)
      return onPointerCancel?.call(event);
    if (event is PointerSignalEvent)
      return onPointerSignal?.call(event);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(FlagsSummary<Function?>(
      'listeners',
      <String, Function?>{
        'down': onPointerDown,
        'move': onPointerMove,
        'up': onPointerUp,
        'hover': onPointerHover,
        'cancel': onPointerCancel,
        'signal': onPointerSignal,
      },
      ifEmpty: '<none>',
    ));
  }
}

/// Calls callbacks in response to pointer events that are exclusive to mice.
///
/// It responds to events that are related to hovering, i.e. when the mouse
/// enters, exits (with or without pressing buttons), or moves over a region
/// without pressing buttons.
///
/// It does not respond to common events that construct gestures, such as when
/// the pointer is pressed, moved, then released or canceled. For these events,
/// use [RenderPointerListener].
///
/// If it has a child, it defers to the child for sizing behavior.
///
/// If it does not have a child, it grows to fit the parent-provided constraints.
///
/// See also:
///
///  * [MouseRegion], a widget that listens to hover events using
///    [RenderMouseRegion].
class RenderMouseRegion extends RenderProxyBox implements MouseTrackerAnnotation {
  /// Creates a render object that forwards pointer events to callbacks.
  ///
  /// All parameters are optional. By default this method creates an opaque
  /// mouse region with no callbacks and cursor being [MouseCursor.defer]. The
  /// [cursor] must not be null.
  RenderMouseRegion({
    this.onEnter,
    this.onHover,
    this.onExit,
    MouseCursor cursor = MouseCursor.defer,
    bool validForMouseTracker = true,
    bool opaque = true,
    RenderBox? child,
  }) : assert(opaque != null),
       assert(cursor != null),
       _cursor = cursor,
       _validForMouseTracker = validForMouseTracker,
       _opaque = opaque,
       super(child);

  @protected
  @override
  bool hitTestSelf(Offset position) => true;

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    return super.hitTest(result, position: position) && _opaque;
  }

  @override
  void handleEvent(PointerEvent event, HitTestEntry entry) {
    assert(debugHandleEvent(event, entry));
    if (onHover != null && event is PointerHoverEvent)
      return onHover!(event);
  }

  /// Whether this object should prevent [RenderMouseRegion]s visually behind it
  /// from detecting the pointer, thus affecting how their [onHover], [onEnter],
  /// and [onExit] behave.
  ///
  /// If [opaque] is true, this object will absorb the mouse pointer and
  /// prevent this object's siblings (or any other objects that are not
  /// ancestors or descendants of this object) from detecting the mouse
  /// pointer even when the pointer is within their areas.
  ///
  /// If [opaque] is false, this object will not affect how [RenderMouseRegion]s
  /// behind it behave, which will detect the mouse pointer as long as the
  /// pointer is within their areas.
  ///
  /// This defaults to true.
  bool get opaque => _opaque;
  bool _opaque;
  set opaque(bool value) {
    if (_opaque != value) {
      _opaque = value;
      // Trigger [MouseTracker]'s device update to recalculate mouse states.
      markNeedsPaint();
    }
  }

  @override
  PointerEnterEventListener? onEnter;

  /// Triggered when a pointer has moved onto or within the region without
  /// buttons pressed.
  ///
  /// This callback is not triggered by the movement of the object.
  PointerHoverEventListener? onHover;

  @override
  PointerExitEventListener? onExit;

  @override
  MouseCursor get cursor => _cursor;
  MouseCursor _cursor;
  set cursor(MouseCursor value) {
    if (_cursor != value) {
      _cursor = value;
      // A repaint is needed in order to trigger a device update of
      // [MouseTracker] so that this new value can be found.
      markNeedsPaint();
    }
  }

  @override
  bool get validForMouseTracker => _validForMouseTracker;
  bool _validForMouseTracker;

  @override
  void attach(PipelineOwner owner) {
    super.attach(owner);
    _validForMouseTracker = true;
  }

  @override
  void detach() {
    // It's possible that the renderObject be detached during mouse events
    // dispatching, set the [MouseTrackerAnnotation.validForMouseTracker] false to prevent
    // the callbacks from being called.
    _validForMouseTracker = false;
    super.detach();
  }

  @override
  Size computeSizeForNoChild(BoxConstraints constraints) {
    return constraints.biggest;
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(FlagsSummary<Function?>(
      'listeners',
      <String, Function?>{
        'enter': onEnter,
        'hover': onHover,
        'exit': onExit,
      },
      ifEmpty: '<none>',
    ));
    properties.add(DiagnosticsProperty<MouseCursor>('cursor', cursor, defaultValue: MouseCursor.defer));
    properties.add(DiagnosticsProperty<bool>('opaque', opaque, defaultValue: true));
    properties.add(FlagProperty('validForMouseTracker', value: validForMouseTracker, defaultValue: true, ifFalse: 'invalid for MouseTracker'));
  }
}

/// Creates a separate display list for its child.
///
/// This render object creates a separate display list for its child, which
/// can improve performance if the subtree repaints at different times than
/// the surrounding parts of the tree. Specifically, when the child does not
/// repaint but its parent does, we can re-use the display list we recorded
/// previously. Similarly, when the child repaints but the surround tree does
/// not, we can re-record its display list without re-recording the display list
/// for the surround tree.
///
/// In some cases, it is necessary to place _two_ (or more) repaint boundaries
/// to get a useful effect. Consider, for example, an e-mail application that
/// shows an unread count and a list of e-mails. Whenever a new e-mail comes in,
/// the list would update, but so would the unread count. If only one of these
/// two parts of the application was behind a repaint boundary, the entire
/// application would repaint each time. On the other hand, if both were behind
/// a repaint boundary, a new e-mail would only change those two parts of the
/// application and the rest of the application would not repaint.
///
/// To tell if a particular RenderRepaintBoundary is useful, run your
/// application in checked mode, interacting with it in typical ways, and then
/// call [debugDumpRenderTree]. Each RenderRepaintBoundary will include the
/// ratio of cases where the repaint boundary was useful vs the cases where it
/// was not. These counts can also be inspected programmatically using
/// [debugAsymmetricPaintCount] and [debugSymmetricPaintCount] respectively.
class RenderRepaintBoundary extends RenderProxyBox {
  /// Creates a repaint boundary around [child].
  RenderRepaintBoundary({ RenderBox? child }) : super(child);

  @override
  bool get isRepaintBoundary => true;

  /// Capture an image of the current state of this render object and its
  /// children.
  ///
  /// The returned [ui.Image] has uncompressed raw RGBA bytes in the dimensions
  /// of the render object, multiplied by the [pixelRatio].
  ///
  /// To use [toImage], the render object must have gone through the paint phase
  /// (i.e. [debugNeedsPaint] must be false).
  ///
  /// The [pixelRatio] describes the scale between the logical pixels and the
  /// size of the output image. It is independent of the
  /// [dart:ui.FlutterView.devicePixelRatio] for the device, so specifying 1.0
  /// (the default) will give you a 1:1 mapping between logical pixels and the
  /// output pixels in the image.
  ///
  /// {@tool snippet}
  ///
  /// The following is an example of how to go from a `GlobalKey` on a
  /// `RepaintBoundary` to a PNG:
  ///
  /// ```dart
  /// class PngHome extends StatefulWidget {
  ///   PngHome({Key? key}) : super(key: key);
  ///
  ///   @override
  ///   _PngHomeState createState() => _PngHomeState();
  /// }
  ///
  /// class _PngHomeState extends State<PngHome> {
  ///   GlobalKey globalKey = GlobalKey();
  ///
  ///   Future<void> _capturePng() async {
  ///     RenderRepaintBoundary boundary = globalKey.currentContext!.findRenderObject()! as RenderRepaintBoundary;
  ///     ui.Image image = await boundary.toImage();
  ///     ByteData? byteData = await image.toByteData(format: ui.ImageByteFormat.png);
  ///     Uint8List pngBytes = byteData!.buffer.asUint8List();
  ///     print(pngBytes);
  ///   }
  ///
  ///   @override
  ///   Widget build(BuildContext context) {
  ///     return RepaintBoundary(
  ///       key: globalKey,
  ///       child: Center(
  ///         child: TextButton(
  ///           child: Text('Hello World', textDirection: TextDirection.ltr),
  ///           onPressed: _capturePng,
  ///         ),
  ///       ),
  ///     );
  ///   }
  /// }
  /// ```
  /// {@end-tool}
  ///
  /// See also:
  ///
  ///  * [OffsetLayer.toImage] for a similar API at the layer level.
  ///  * [dart:ui.Scene.toImage] for more information about the image returned.
  Future<ui.Image> toImage({ double pixelRatio = 1.0 }) {
    assert(!debugNeedsPaint);
    final OffsetLayer offsetLayer = layer! as OffsetLayer;
    return offsetLayer.toImage(Offset.zero & size, pixelRatio: pixelRatio);
  }


  /// The number of times that this render object repainted at the same time as
  /// its parent. Repaint boundaries are only useful when the parent and child
  /// paint at different times. When both paint at the same time, the repaint
  /// boundary is redundant, and may be actually making performance worse.
  ///
  /// Only valid when asserts are enabled. In release builds, always returns
  /// zero.
  ///
  /// Can be reset using [debugResetMetrics]. See [debugAsymmetricPaintCount]
  /// for the corresponding count of times where only the parent or only the
  /// child painted.
  int get debugSymmetricPaintCount => _debugSymmetricPaintCount;
  int _debugSymmetricPaintCount = 0;

  /// The number of times that either this render object repainted without the
  /// parent being painted, or the parent repainted without this object being
  /// painted. When a repaint boundary is used at a seam in the render tree
  /// where the parent tends to repaint at entirely different times than the
  /// child, it can improve performance by reducing the number of paint
  /// operations that have to be recorded each frame.
  ///
  /// Only valid when asserts are enabled. In release builds, always returns
  /// zero.
  ///
  /// Can be reset using [debugResetMetrics]. See [debugSymmetricPaintCount] for
  /// the corresponding count of times where both the parent and the child
  /// painted together.
  int get debugAsymmetricPaintCount => _debugAsymmetricPaintCount;
  int _debugAsymmetricPaintCount = 0;

  /// Resets the [debugSymmetricPaintCount] and [debugAsymmetricPaintCount]
  /// counts to zero.
  ///
  /// Only valid when asserts are enabled. Does nothing in release builds.
  void debugResetMetrics() {
    assert(() {
      _debugSymmetricPaintCount = 0;
      _debugAsymmetricPaintCount = 0;
      return true;
    }());
  }

  @override
  void debugRegisterRepaintBoundaryPaint({ bool includedParent = true, bool includedChild = false }) {
    assert(() {
      if (includedParent && includedChild)
        _debugSymmetricPaintCount += 1;
      else
        _debugAsymmetricPaintCount += 1;
      return true;
    }());
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    bool inReleaseMode = true;
    assert(() {
      inReleaseMode = false;
      if (debugSymmetricPaintCount + debugAsymmetricPaintCount == 0) {
        properties.add(MessageProperty('usefulness ratio', 'no metrics collected yet (never painted)'));
      } else {
        final double fraction = debugAsymmetricPaintCount / (debugSymmetricPaintCount + debugAsymmetricPaintCount);
        final String diagnosis;
        if (debugSymmetricPaintCount + debugAsymmetricPaintCount < 5) {
          diagnosis = 'insufficient data to draw conclusion (less than five repaints)';
        } else if (fraction > 0.9) {
          diagnosis = 'this is an outstandingly useful repaint boundary and should definitely be kept';
        } else if (fraction > 0.5) {
          diagnosis = 'this is a useful repaint boundary and should be kept';
        } else if (fraction > 0.30) {
          diagnosis = 'this repaint boundary is probably useful, but maybe it would be more useful in tandem with adding more repaint boundaries elsewhere';
        } else if (fraction > 0.1) {
          diagnosis = 'this repaint boundary does sometimes show value, though currently not that often';
        } else if (debugAsymmetricPaintCount == 0) {
          diagnosis = 'this repaint boundary is astoundingly ineffectual and should be removed';
        } else {
          diagnosis = 'this repaint boundary is not very effective and should probably be removed';
        }
        properties.add(PercentProperty('metrics', fraction, unit: 'useful', tooltip: '$debugSymmetricPaintCount bad vs $debugAsymmetricPaintCount good'));
        properties.add(MessageProperty('diagnosis', diagnosis));
      }
      return true;
    }());
    if (inReleaseMode)
      properties.add(DiagnosticsNode.message('(run in checked mode to collect repaint boundary statistics)'));
  }
}

/// A render object that is invisible during hit testing.
///
/// When [ignoring] is true, this render object (and its subtree) is invisible
/// to hit testing. It still consumes space during layout and paints its child
/// as usual. It just cannot be the target of located events, because its render
/// object returns false from [hitTest].
///
/// When [ignoringSemantics] is true, the subtree will be invisible to
/// the semantics layer (and thus e.g. accessibility tools). If
/// [ignoringSemantics] is null, it uses the value of [ignoring].
///
/// See also:
///
///  * [RenderAbsorbPointer], which takes the pointer events but prevents any
///    nodes in the subtree from seeing them.
class RenderIgnorePointer extends RenderProxyBox {
  /// Creates a render object that is invisible to hit testing.
  ///
  /// The [ignoring] argument must not be null. If [ignoringSemantics] is null,
  /// this render object will be ignored for semantics if [ignoring] is true.
  RenderIgnorePointer({
    RenderBox? child,
    bool ignoring = true,
    bool? ignoringSemantics,
  }) : _ignoring = ignoring,
       _ignoringSemantics = ignoringSemantics,
       super(child) {
    assert(_ignoring != null);
  }

  /// Whether this render object is ignored during hit testing.
  ///
  /// Regardless of whether this render object is ignored during hit testing, it
  /// will still consume space during layout and be visible during painting.
  bool get ignoring => _ignoring;
  bool _ignoring;
  set ignoring(bool value) {
    assert(value != null);
    if (value == _ignoring)
      return;
    _ignoring = value;
    if (_ignoringSemantics == null || !_ignoringSemantics!)
      markNeedsSemanticsUpdate();
  }

  /// Whether the semantics of this render object is ignored when compiling the semantics tree.
  ///
  /// If null, defaults to value of [ignoring].
  ///
  /// See [SemanticsNode] for additional information about the semantics tree.
  bool? get ignoringSemantics => _ignoringSemantics;
  bool? _ignoringSemantics;
  set ignoringSemantics(bool? value) {
    if (value == _ignoringSemantics)
      return;
    final bool oldEffectiveValue = _effectiveIgnoringSemantics;
    _ignoringSemantics = value;
    if (oldEffectiveValue != _effectiveIgnoringSemantics)
      markNeedsSemanticsUpdate();
  }

  bool get _effectiveIgnoringSemantics => ignoringSemantics ?? ignoring;

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    return !ignoring && super.hitTest(result, position: position);
  }

  // TODO(ianh): figure out a way to still include labels and flags in
  // descendants, just make them non-interactive, even when
  // _effectiveIgnoringSemantics is true
  @override
  void visitChildrenForSemantics(RenderObjectVisitor visitor) {
    if (child != null && !_effectiveIgnoringSemantics)
      visitor(child!);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<bool>('ignoring', ignoring));
    properties.add(
      DiagnosticsProperty<bool>(
        'ignoringSemantics',
        _effectiveIgnoringSemantics,
        description: ignoringSemantics == null ? 'implicitly $_effectiveIgnoringSemantics' : null,
      ),
    );
  }
}

/// Lays the child out as if it was in the tree, but without painting anything,
/// without making the child available for hit testing, and without taking any
/// room in the parent.
class RenderOffstage extends RenderProxyBox {
  /// Creates an offstage render object.
  RenderOffstage({
    bool offstage = true,
    RenderBox? child,
  }) : assert(offstage != null),
       _offstage = offstage,
       super(child);

  /// Whether the child is hidden from the rest of the tree.
  ///
  /// If true, the child is laid out as if it was in the tree, but without
  /// painting anything, without making the child available for hit testing, and
  /// without taking any room in the parent.
  ///
  /// If false, the child is included in the tree as normal.
  bool get offstage => _offstage;
  bool _offstage;
  set offstage(bool value) {
    assert(value != null);
    if (value == _offstage)
      return;
    _offstage = value;
    markNeedsLayoutForSizedByParentChange();
  }

  @override
  double computeMinIntrinsicWidth(double height) {
    if (offstage)
      return 0.0;
    return super.computeMinIntrinsicWidth(height);
  }

  @override
  double computeMaxIntrinsicWidth(double height) {
    if (offstage)
      return 0.0;
    return super.computeMaxIntrinsicWidth(height);
  }

  @override
  double computeMinIntrinsicHeight(double width) {
    if (offstage)
      return 0.0;
    return super.computeMinIntrinsicHeight(width);
  }

  @override
  double computeMaxIntrinsicHeight(double width) {
    if (offstage)
      return 0.0;
    return super.computeMaxIntrinsicHeight(width);
  }

  @override
  double? computeDistanceToActualBaseline(TextBaseline baseline) {
    if (offstage)
      return null;
    return super.computeDistanceToActualBaseline(baseline);
  }

  @override
  bool get sizedByParent => offstage;

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    if (offstage) {
      return constraints.smallest;
    }
    return super.computeDryLayout(constraints);
  }


  @override
  void performResize() {
    assert(offstage);
    super.performResize();
  }

  @override
  void performLayout() {
    if (offstage) {
      child?.layout(constraints);
    } else {
      super.performLayout();
    }
  }

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    return !offstage && super.hitTest(result, position: position);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (offstage)
      return;
    super.paint(context, offset);
  }

  @override
  void visitChildrenForSemantics(RenderObjectVisitor visitor) {
    if (offstage)
      return;
    super.visitChildrenForSemantics(visitor);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<bool>('offstage', offstage));
  }

  @override
  List<DiagnosticsNode> debugDescribeChildren() {
    if (child == null)
      return <DiagnosticsNode>[];
    return <DiagnosticsNode>[
      child!.toDiagnosticsNode(
        name: 'child',
        style: offstage ? DiagnosticsTreeStyle.offstage : DiagnosticsTreeStyle.sparse,
      ),
    ];
  }
}

/// A render object that absorbs pointers during hit testing.
///
/// When [absorbing] is true, this render object prevents its subtree from
/// receiving pointer events by terminating hit testing at itself. It still
/// consumes space during layout and paints its child as usual. It just prevents
/// its children from being the target of located events, because its render
/// object returns true from [hitTest].
///
/// See also:
///
///  * [RenderIgnorePointer], which has the opposite effect: removing the
///    subtree from considering entirely for the purposes of hit testing.
class RenderAbsorbPointer extends RenderProxyBox {
  /// Creates a render object that absorbs pointers during hit testing.
  ///
  /// The [absorbing] argument must not be null.
  RenderAbsorbPointer({
    RenderBox? child,
    bool absorbing = true,
    bool? ignoringSemantics,
  }) : assert(absorbing != null),
       _absorbing = absorbing,
       _ignoringSemantics = ignoringSemantics,
       super(child);

  /// Whether this render object absorbs pointers during hit testing.
  ///
  /// Regardless of whether this render object absorbs pointers during hit
  /// testing, it will still consume space during layout and be visible during
  /// painting.
  bool get absorbing => _absorbing;
  bool _absorbing;
  set absorbing(bool value) {
    if (_absorbing == value)
      return;
    _absorbing = value;
    if (ignoringSemantics == null)
      markNeedsSemanticsUpdate();
  }

  /// Whether the semantics of this render object is ignored when compiling the semantics tree.
  ///
  /// If null, defaults to value of [absorbing].
  ///
  /// See [SemanticsNode] for additional information about the semantics tree.
  bool? get ignoringSemantics => _ignoringSemantics;
  bool? _ignoringSemantics;
  set ignoringSemantics(bool? value) {
    if (value == _ignoringSemantics)
      return;
    final bool oldEffectiveValue = _effectiveIgnoringSemantics;
    _ignoringSemantics = value;
    if (oldEffectiveValue != _effectiveIgnoringSemantics)
      markNeedsSemanticsUpdate();
  }

  bool get _effectiveIgnoringSemantics => ignoringSemantics ?? absorbing;

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    return absorbing
        ? size.contains(position)
        : super.hitTest(result, position: position);
  }

  @override
  void visitChildrenForSemantics(RenderObjectVisitor visitor) {
    if (child != null && !_effectiveIgnoringSemantics)
      visitor(child!);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<bool>('absorbing', absorbing));
    properties.add(
      DiagnosticsProperty<bool>(
        'ignoringSemantics',
        _effectiveIgnoringSemantics,
        description: ignoringSemantics == null ? 'implicitly $_effectiveIgnoringSemantics' : null,
      ),
    );
  }
}

/// Holds opaque meta data in the render tree.
///
/// Useful for decorating the render tree with information that will be consumed
/// later. For example, you could store information in the render tree that will
/// be used when the user interacts with the render tree but has no visual
/// impact prior to the interaction.
class RenderMetaData extends RenderProxyBoxWithHitTestBehavior {
  /// Creates a render object that hold opaque meta data.
  ///
  /// The [behavior] argument defaults to [HitTestBehavior.deferToChild].
  RenderMetaData({
    this.metaData,
    HitTestBehavior behavior = HitTestBehavior.deferToChild,
    RenderBox? child,
  }) : super(behavior: behavior, child: child);

  /// Opaque meta data ignored by the render tree.
  dynamic metaData;

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<dynamic>('metaData', metaData));
  }
}

/// Listens for the specified gestures from the semantics server (e.g.
/// an accessibility tool).
class RenderSemanticsGestureHandler extends RenderProxyBoxWithHitTestBehavior {
  /// Creates a render object that listens for specific semantic gestures.
  ///
  /// The [scrollFactor] and [behavior] arguments must not be null.
  RenderSemanticsGestureHandler({
    RenderBox? child,
    GestureTapCallback? onTap,
    GestureLongPressCallback? onLongPress,
    GestureDragUpdateCallback? onHorizontalDragUpdate,
    GestureDragUpdateCallback? onVerticalDragUpdate,
    this.scrollFactor = 0.8,
    HitTestBehavior behavior = HitTestBehavior.deferToChild,
  }) : assert(scrollFactor != null),
       _onTap = onTap,
       _onLongPress = onLongPress,
       _onHorizontalDragUpdate = onHorizontalDragUpdate,
       _onVerticalDragUpdate = onVerticalDragUpdate,
       super(behavior: behavior, child: child);

  /// If non-null, the set of actions to allow. Other actions will be omitted,
  /// even if their callback is provided.
  ///
  /// For example, if [onTap] is non-null but [validActions] does not contain
  /// [SemanticsAction.tap], then the semantic description of this node will
  /// not claim to support taps.
  ///
  /// This is normally used to filter the actions made available by
  /// [onHorizontalDragUpdate] and [onVerticalDragUpdate]. Normally, these make
  /// both the right and left, or up and down, actions available. For example,
  /// if [onHorizontalDragUpdate] is set but [validActions] only contains
  /// [SemanticsAction.scrollLeft], then the [SemanticsAction.scrollRight]
  /// action will be omitted.
  Set<SemanticsAction>? get validActions => _validActions;
  Set<SemanticsAction>? _validActions;
  set validActions(Set<SemanticsAction>? value) {
    if (setEquals<SemanticsAction>(value, _validActions))
      return;
    _validActions = value;
    markNeedsSemanticsUpdate();
  }

  /// Called when the user taps on the render object.
  GestureTapCallback? get onTap => _onTap;
  GestureTapCallback? _onTap;
  set onTap(GestureTapCallback? value) {
    if (_onTap == value)
      return;
    final bool hadHandler = _onTap != null;
    _onTap = value;
    if ((value != null) != hadHandler)
      markNeedsSemanticsUpdate();
  }

  /// Called when the user presses on the render object for a long period of time.
  GestureLongPressCallback? get onLongPress => _onLongPress;
  GestureLongPressCallback? _onLongPress;
  set onLongPress(GestureLongPressCallback? value) {
    if (_onLongPress == value)
      return;
    final bool hadHandler = _onLongPress != null;
    _onLongPress = value;
    if ((value != null) != hadHandler)
      markNeedsSemanticsUpdate();
  }

  /// Called when the user scrolls to the left or to the right.
  GestureDragUpdateCallback? get onHorizontalDragUpdate => _onHorizontalDragUpdate;
  GestureDragUpdateCallback? _onHorizontalDragUpdate;
  set onHorizontalDragUpdate(GestureDragUpdateCallback? value) {
    if (_onHorizontalDragUpdate == value)
      return;
    final bool hadHandler = _onHorizontalDragUpdate != null;
    _onHorizontalDragUpdate = value;
    if ((value != null) != hadHandler)
      markNeedsSemanticsUpdate();
  }

  /// Called when the user scrolls up or down.
  GestureDragUpdateCallback? get onVerticalDragUpdate => _onVerticalDragUpdate;
  GestureDragUpdateCallback? _onVerticalDragUpdate;
  set onVerticalDragUpdate(GestureDragUpdateCallback? value) {
    if (_onVerticalDragUpdate == value)
      return;
    final bool hadHandler = _onVerticalDragUpdate != null;
    _onVerticalDragUpdate = value;
    if ((value != null) != hadHandler)
      markNeedsSemanticsUpdate();
  }

  /// The fraction of the dimension of this render box to use when
  /// scrolling. For example, if this is 0.8 and the box is 200 pixels
  /// wide, then when a left-scroll action is received from the
  /// accessibility system, it will translate into a 160 pixel
  /// leftwards drag.
  double scrollFactor;

  @override
  void describeSemanticsConfiguration(SemanticsConfiguration config) {
    super.describeSemanticsConfiguration(config);

    if (onTap != null && _isValidAction(SemanticsAction.tap))
      config.onTap = onTap;
    if (onLongPress != null && _isValidAction(SemanticsAction.longPress))
      config.onLongPress = onLongPress;
    if (onHorizontalDragUpdate != null) {
      if (_isValidAction(SemanticsAction.scrollRight))
        config.onScrollRight = _performSemanticScrollRight;
      if (_isValidAction(SemanticsAction.scrollLeft))
        config.onScrollLeft = _performSemanticScrollLeft;
    }
    if (onVerticalDragUpdate != null) {
      if (_isValidAction(SemanticsAction.scrollUp))
        config.onScrollUp = _performSemanticScrollUp;
      if (_isValidAction(SemanticsAction.scrollDown))
        config.onScrollDown = _performSemanticScrollDown;
    }
  }

  bool _isValidAction(SemanticsAction action) {
    return validActions == null || validActions!.contains(action);
  }

  void _performSemanticScrollLeft() {
    if (onHorizontalDragUpdate != null) {
      final double primaryDelta = size.width * -scrollFactor;
      onHorizontalDragUpdate!(DragUpdateDetails(
        delta: Offset(primaryDelta, 0.0), primaryDelta: primaryDelta,
        globalPosition: localToGlobal(size.center(Offset.zero)),
      ));
    }
  }

  void _performSemanticScrollRight() {
    if (onHorizontalDragUpdate != null) {
      final double primaryDelta = size.width * scrollFactor;
      onHorizontalDragUpdate!(DragUpdateDetails(
        delta: Offset(primaryDelta, 0.0), primaryDelta: primaryDelta,
        globalPosition: localToGlobal(size.center(Offset.zero)),
      ));
    }
  }

  void _performSemanticScrollUp() {
    if (onVerticalDragUpdate != null) {
      final double primaryDelta = size.height * -scrollFactor;
      onVerticalDragUpdate!(DragUpdateDetails(
        delta: Offset(0.0, primaryDelta), primaryDelta: primaryDelta,
        globalPosition: localToGlobal(size.center(Offset.zero)),
      ));
    }
  }

  void _performSemanticScrollDown() {
    if (onVerticalDragUpdate != null) {
      final double primaryDelta = size.height * scrollFactor;
      onVerticalDragUpdate!(DragUpdateDetails(
        delta: Offset(0.0, primaryDelta), primaryDelta: primaryDelta,
        globalPosition: localToGlobal(size.center(Offset.zero)),
      ));
    }
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    final List<String> gestures = <String>[
      if (onTap != null) 'tap',
      if (onLongPress != null) 'long press',
      if (onHorizontalDragUpdate != null) 'horizontal scroll',
      if (onVerticalDragUpdate != null) 'vertical scroll',
    ];
    if (gestures.isEmpty)
      gestures.add('<none>');
    properties.add(IterableProperty<String>('gestures', gestures));
  }
}

/// Add annotations to the [SemanticsNode] for this subtree.
class RenderSemanticsAnnotations extends RenderProxyBox {
  /// Creates a render object that attaches a semantic annotation.
  ///
  /// The [container] argument must not be null.
  ///
  /// If the [label] is not null, the [textDirection] must also not be null.
  RenderSemanticsAnnotations({
    RenderBox? child,
    bool container = false,
    bool explicitChildNodes = false,
    bool excludeSemantics = false,
    bool? enabled,
    bool? checked,
    bool? toggled,
    bool? selected,
    bool? button,
    bool? slider,
    bool? link,
    bool? header,
    bool? textField,
    bool? readOnly,
    bool? focusable,
    bool? focused,
    bool? inMutuallyExclusiveGroup,
    bool? obscured,
    bool? multiline,
    bool? scopesRoute,
    bool? namesRoute,
    bool? hidden,
    bool? image,
    bool? liveRegion,
    int? maxValueLength,
    int? currentValueLength,
    String? label,
    String? value,
    String? increasedValue,
    String? decreasedValue,
    String? hint,
    SemanticsHintOverrides? hintOverrides,
    TextDirection? textDirection,
    SemanticsSortKey? sortKey,
    SemanticsTag? tagForChildren,
    VoidCallback? onTap,
    VoidCallback? onDismiss,
    VoidCallback? onLongPress,
    VoidCallback? onScrollLeft,
    VoidCallback? onScrollRight,
    VoidCallback? onScrollUp,
    VoidCallback? onScrollDown,
    VoidCallback? onIncrease,
    VoidCallback? onDecrease,
    VoidCallback? onCopy,
    VoidCallback? onCut,
    VoidCallback? onPaste,
    MoveCursorHandler? onMoveCursorForwardByCharacter,
    MoveCursorHandler? onMoveCursorBackwardByCharacter,
    MoveCursorHandler? onMoveCursorForwardByWord,
    MoveCursorHandler? onMoveCursorBackwardByWord,
    SetSelectionHandler? onSetSelection,
    VoidCallback? onDidGainAccessibilityFocus,
    VoidCallback? onDidLoseAccessibilityFocus,
    Map<CustomSemanticsAction, VoidCallback>? customSemanticsActions,
  }) : assert(container != null),
       _container = container,
       _explicitChildNodes = explicitChildNodes,
       _excludeSemantics = excludeSemantics,
       _enabled = enabled,
       _checked = checked,
       _toggled = toggled,
       _selected = selected,
       _button = button,
       _slider = slider,
       _link = link,
       _header = header,
       _textField = textField,
       _readOnly = readOnly,
       _focusable = focusable,
       _focused = focused,
       _inMutuallyExclusiveGroup = inMutuallyExclusiveGroup,
       _obscured = obscured,
       _multiline = multiline,
       _scopesRoute = scopesRoute,
       _namesRoute = namesRoute,
       _liveRegion = liveRegion,
       _maxValueLength = maxValueLength,
       _currentValueLength = currentValueLength,
       _hidden = hidden,
       _image = image,
       _onDismiss = onDismiss,
       _label = label,
       _value = value,
       _increasedValue = increasedValue,
       _decreasedValue = decreasedValue,
       _hint = hint,
       _hintOverrides = hintOverrides,
       _textDirection = textDirection,
       _sortKey = sortKey,
       _tagForChildren = tagForChildren,
       _onTap = onTap,
       _onLongPress = onLongPress,
       _onScrollLeft = onScrollLeft,
       _onScrollRight = onScrollRight,
       _onScrollUp = onScrollUp,
       _onScrollDown = onScrollDown,
       _onIncrease = onIncrease,
       _onDecrease = onDecrease,
       _onCopy = onCopy,
       _onCut = onCut,
       _onPaste = onPaste,
       _onMoveCursorForwardByCharacter = onMoveCursorForwardByCharacter,
       _onMoveCursorBackwardByCharacter = onMoveCursorBackwardByCharacter,
       _onMoveCursorForwardByWord = onMoveCursorForwardByWord,
       _onMoveCursorBackwardByWord = onMoveCursorBackwardByWord,
       _onSetSelection = onSetSelection,
       _onDidGainAccessibilityFocus = onDidGainAccessibilityFocus,
       _onDidLoseAccessibilityFocus = onDidLoseAccessibilityFocus,
       _customSemanticsActions = customSemanticsActions,
       super(child);

  /// If 'container' is true, this [RenderObject] will introduce a new
  /// node in the semantics tree. Otherwise, the semantics will be
  /// merged with the semantics of any ancestors.
  ///
  /// Whether descendants of this [RenderObject] can add their semantic information
  /// to the [SemanticsNode] introduced by this configuration is controlled by
  /// [explicitChildNodes].
  bool get container => _container;
  bool _container;
  set container(bool value) {
    assert(value != null);
    if (container == value)
      return;
    _container = value;
    markNeedsSemanticsUpdate();
  }

  /// Whether descendants of this [RenderObject] are allowed to add semantic
  /// information to the [SemanticsNode] annotated by this widget.
  ///
  /// When set to false descendants are allowed to annotate [SemanticsNode]s of
  /// their parent with the semantic information they want to contribute to the
  /// semantic tree.
  /// When set to true the only way for descendants to contribute semantic
  /// information to the semantic tree is to introduce new explicit
  /// [SemanticsNode]s to the tree.
  ///
  /// This setting is often used in combination with
  /// [SemanticsConfiguration.isSemanticBoundary] to create semantic boundaries
  /// that are either writable or not for children.
  bool get explicitChildNodes => _explicitChildNodes;
  bool _explicitChildNodes;
  set explicitChildNodes(bool value) {
    assert(value != null);
    if (_explicitChildNodes == value)
      return;
    _explicitChildNodes = value;
    markNeedsSemanticsUpdate();
  }

  /// Whether descendants of this [RenderObject] should have their semantic
  /// information ignored.
  ///
  /// When this flag is set to true, all child semantics nodes are ignored.
  /// This can be used as a convenience for cases where a child is wrapped in
  /// an [ExcludeSemantics] widget and then another [Semantics] widget.
  bool get excludeSemantics => _excludeSemantics;
  bool _excludeSemantics;
  set excludeSemantics(bool value) {
    assert(value != null);
    if (_excludeSemantics == value)
      return;
    _excludeSemantics = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsFlag.hasCheckedState] semantic to true and
  /// the [SemanticsConfiguration.isChecked] semantic to the given value.
  bool? get checked => _checked;
  bool? _checked;
  set checked(bool? value) {
    if (checked == value)
      return;
    _checked = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsFlag.hasEnabledState] semantic to true and
  /// the [SemanticsConfiguration.isEnabled] semantic to the given value.
  bool? get enabled => _enabled;
  bool? _enabled;
  set enabled(bool? value) {
    if (enabled == value)
      return;
    _enabled = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isSelected] semantic to the
  /// given value.
  bool? get selected => _selected;
  bool? _selected;
  set selected(bool? value) {
    if (selected == value)
      return;
    _selected = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isButton] semantic to the
  /// given value.
  bool? get button => _button;
  bool? _button;
  set button(bool? value) {
    if (button == value)
      return;
    _button = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isSlider] semantic to the
  /// given value.
  bool? get slider => _slider;
  bool? _slider;
  set slider(bool? value) {
    if (slider == value)
      return;
    _slider = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isLink] semantic to the
  /// given value.
  bool? get link => _link;
  bool? _link;
  set link(bool? value) {
    if (link == value)
      return;
    _link = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isHeader] semantic to the
  /// given value.
  bool? get header => _header;
  bool? _header;
  set header(bool? value) {
    if (header == value)
      return;
    _header = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isTextField] semantic to the
  /// given value.
  bool? get textField => _textField;
  bool? _textField;
  set textField(bool? value) {
    if (textField == value)
      return;
    _textField = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isReadOnly] semantic to the
  /// given value.
  bool? get readOnly => _readOnly;
  bool? _readOnly;
  set readOnly(bool? value) {
    if (readOnly == value)
      return;
    _readOnly = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isFocusable] semantic to the
  /// given value.
  bool? get focusable => _focusable;
  bool? _focusable;
  set focusable(bool? value) {
    if (focusable == value)
      return;
    _focusable = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isFocused] semantic to the
  /// given value.
  bool? get focused => _focused;
  bool? _focused;
  set focused(bool? value) {
    if (focused == value)
      return;
    _focused = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isInMutuallyExclusiveGroup]
  /// semantic to the given value.
  bool? get inMutuallyExclusiveGroup => _inMutuallyExclusiveGroup;
  bool? _inMutuallyExclusiveGroup;
  set inMutuallyExclusiveGroup(bool? value) {
    if (inMutuallyExclusiveGroup == value)
      return;
    _inMutuallyExclusiveGroup = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isObscured] semantic to the
  /// given value.
  bool? get obscured => _obscured;
  bool? _obscured;
  set obscured(bool? value) {
    if (obscured == value)
      return;
    _obscured = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.isMultiline] semantic to the given
  /// value.
  bool? get multiline => _multiline;
  bool? _multiline;
  set multiline(bool? value) {
    if (multiline == value)
      return;
    _multiline = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.scopesRoute] semantic to the
  /// give value.
  bool? get scopesRoute => _scopesRoute;
  bool? _scopesRoute;
  set scopesRoute(bool? value) {
    if (scopesRoute == value)
      return;
    _scopesRoute = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.namesRoute] semantic to the
  /// give value.
  bool? get namesRoute => _namesRoute;
  bool? _namesRoute;
  set namesRoute(bool? value) {
    if (_namesRoute == value)
      return;
    _namesRoute = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isHidden] semantic to the
  /// given value.
  bool? get hidden => _hidden;
  bool? _hidden;
  set hidden(bool? value) {
    if (hidden == value)
      return;
    _hidden = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isImage] semantic to the
  /// given value.
  bool? get image => _image;
  bool? _image;
  set image(bool? value) {
    if (_image == value)
      return;
    _image = value;
  }

  /// If non-null, sets the [SemanticsConfiguration.liveRegion] semantic to
  /// the given value.
  bool? get liveRegion => _liveRegion;
  bool? _liveRegion;
  set liveRegion(bool? value) {
    if (_liveRegion == value)
      return;
    _liveRegion = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.maxValueLength] semantic to the given
  /// value.
  int? get maxValueLength => _maxValueLength;
  int? _maxValueLength;
  set maxValueLength(int? value) {
    if (_maxValueLength == value)
      return;
    _maxValueLength = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.currentValueLength] semantic to the
  /// given value.
  int? get currentValueLength => _currentValueLength;
  int? _currentValueLength;
  set currentValueLength(int? value) {
    if (_currentValueLength == value)
      return;
    _currentValueLength = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.isToggled] semantic to the given
  /// value.
  bool? get toggled => _toggled;
  bool? _toggled;
  set toggled(bool? value) {
    if (_toggled == value)
      return;
    _toggled = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.label] semantic to the given value.
  ///
  /// The reading direction is given by [textDirection].
  String? get label => _label;
  String? _label;
  set label(String? value) {
    if (_label == value)
      return;
    _label = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.value] semantic to the given value.
  ///
  /// The reading direction is given by [textDirection].
  String? get value => _value;
  String? _value;
  set value(String? value) {
    if (_value == value)
      return;
    _value = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.increasedValue] semantic to the given
  /// value.
  ///
  /// The reading direction is given by [textDirection].
  String? get increasedValue => _increasedValue;
  String? _increasedValue;
  set increasedValue(String? value) {
    if (_increasedValue == value)
      return;
    _increasedValue = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.decreasedValue] semantic to the given
  /// value.
  ///
  /// The reading direction is given by [textDirection].
  String? get decreasedValue => _decreasedValue;
  String? _decreasedValue;
  set decreasedValue(String? value) {
    if (_decreasedValue == value)
      return;
    _decreasedValue = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.hint] semantic to the given value.
  ///
  /// The reading direction is given by [textDirection].
  String? get hint => _hint;
  String? _hint;
  set hint(String? value) {
    if (_hint == value)
      return;
    _hint = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsConfiguration.hintOverrides] to the given value.
  SemanticsHintOverrides? get hintOverrides => _hintOverrides;
  SemanticsHintOverrides? _hintOverrides;
  set hintOverrides(SemanticsHintOverrides? value) {
    if (_hintOverrides == value)
      return;
    _hintOverrides = value;
    markNeedsSemanticsUpdate();
  }

  /// If non-null, sets the [SemanticsNode.textDirection] semantic to the given value.
  ///
  /// This must not be null if [label], [hint], [value], [increasedValue], or
  /// [decreasedValue] are not null.
  TextDirection? get textDirection => _textDirection;
  TextDirection? _textDirection;
  set textDirection(TextDirection? value) {
    if (textDirection == value)
      return;
    _textDirection = value;
    markNeedsSemanticsUpdate();
  }

  /// Sets the [SemanticsNode.sortKey] to the given value.
  ///
  /// This defines how this node is sorted among the sibling semantics nodes
  /// to determine the order in which they are traversed by the accessibility
  /// services on the platform (e.g. VoiceOver on iOS and TalkBack on Android).
  SemanticsSortKey? get sortKey => _sortKey;
  SemanticsSortKey? _sortKey;
  set sortKey(SemanticsSortKey? value) {
    if (sortKey == value)
      return;
    _sortKey = value;
    markNeedsSemanticsUpdate();
  }

  /// Adds a semenatics tag to the semantics subtree.
  SemanticsTag? get tagForChildren => _tagForChildren;
  SemanticsTag? _tagForChildren;
  set tagForChildren(SemanticsTag? value) {
    if (_tagForChildren == value)
      return;
    markNeedsSemanticsUpdate();
    _tagForChildren = value;
  }

  /// The handler for [SemanticsAction.tap].
  ///
  /// This is the semantic equivalent of a user briefly tapping the screen with
  /// the finger without moving it. For example, a button should implement this
  /// action.
  ///
  /// VoiceOver users on iOS and TalkBack users on Android can trigger this
  /// action by double-tapping the screen while an element is focused.
  VoidCallback? get onTap => _onTap;
  VoidCallback? _onTap;
  set onTap(VoidCallback? handler) {
    if (_onTap == handler)
      return;
    final bool hadValue = _onTap != null;
    _onTap = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.dismiss].
  ///
  /// This is a request to dismiss the currently focused node.
  ///
  /// TalkBack users on Android can trigger this action in the local context
  /// menu, and VoiceOver users on iOS can trigger this action with a standard
  /// gesture or menu option.
  VoidCallback? get onDismiss => _onDismiss;
  VoidCallback? _onDismiss;
  set onDismiss(VoidCallback? handler) {
    if (_onDismiss == handler)
      return;
    final bool hadValue = _onDismiss != null;
    _onDismiss = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.longPress].
  ///
  /// This is the semantic equivalent of a user pressing and holding the screen
  /// with the finger for a few seconds without moving it.
  ///
  /// VoiceOver users on iOS and TalkBack users on Android can trigger this
  /// action by double-tapping the screen without lifting the finger after the
  /// second tap.
  VoidCallback? get onLongPress => _onLongPress;
  VoidCallback? _onLongPress;
  set onLongPress(VoidCallback? handler) {
    if (_onLongPress == handler)
      return;
    final bool hadValue = _onLongPress != null;
    _onLongPress = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.scrollLeft].
  ///
  /// This is the semantic equivalent of a user moving their finger across the
  /// screen from right to left. It should be recognized by controls that are
  /// horizontally scrollable.
  ///
  /// VoiceOver users on iOS can trigger this action by swiping left with three
  /// fingers. TalkBack users on Android can trigger this action by swiping
  /// right and then left in one motion path. On Android, [onScrollUp] and
  /// [onScrollLeft] share the same gesture. Therefore, only on of them should
  /// be provided.
  VoidCallback? get onScrollLeft => _onScrollLeft;
  VoidCallback? _onScrollLeft;
  set onScrollLeft(VoidCallback? handler) {
    if (_onScrollLeft == handler)
      return;
    final bool hadValue = _onScrollLeft != null;
    _onScrollLeft = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.scrollRight].
  ///
  /// This is the semantic equivalent of a user moving their finger across the
  /// screen from left to right. It should be recognized by controls that are
  /// horizontally scrollable.
  ///
  /// VoiceOver users on iOS can trigger this action by swiping right with three
  /// fingers. TalkBack users on Android can trigger this action by swiping
  /// left and then right in one motion path. On Android, [onScrollDown] and
  /// [onScrollRight] share the same gesture. Therefore, only on of them should
  /// be provided.
  VoidCallback? get onScrollRight => _onScrollRight;
  VoidCallback? _onScrollRight;
  set onScrollRight(VoidCallback? handler) {
    if (_onScrollRight == handler)
      return;
    final bool hadValue = _onScrollRight != null;
    _onScrollRight = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.scrollUp].
  ///
  /// This is the semantic equivalent of a user moving their finger across the
  /// screen from bottom to top. It should be recognized by controls that are
  /// vertically scrollable.
  ///
  /// VoiceOver users on iOS can trigger this action by swiping up with three
  /// fingers. TalkBack users on Android can trigger this action by swiping
  /// right and then left in one motion path. On Android, [onScrollUp] and
  /// [onScrollLeft] share the same gesture. Therefore, only on of them should
  /// be provided.
  VoidCallback? get onScrollUp => _onScrollUp;
  VoidCallback? _onScrollUp;
  set onScrollUp(VoidCallback? handler) {
    if (_onScrollUp == handler)
      return;
    final bool hadValue = _onScrollUp != null;
    _onScrollUp = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.scrollDown].
  ///
  /// This is the semantic equivalent of a user moving their finger across the
  /// screen from top to bottom. It should be recognized by controls that are
  /// vertically scrollable.
  ///
  /// VoiceOver users on iOS can trigger this action by swiping down with three
  /// fingers. TalkBack users on Android can trigger this action by swiping
  /// left and then right in one motion path. On Android, [onScrollDown] and
  /// [onScrollRight] share the same gesture. Therefore, only on of them should
  /// be provided.
  VoidCallback? get onScrollDown => _onScrollDown;
  VoidCallback? _onScrollDown;
  set onScrollDown(VoidCallback? handler) {
    if (_onScrollDown == handler)
      return;
    final bool hadValue = _onScrollDown != null;
    _onScrollDown = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.increase].
  ///
  /// This is a request to increase the value represented by the widget. For
  /// example, this action might be recognized by a slider control.
  ///
  /// VoiceOver users on iOS can trigger this action by swiping up with one
  /// finger. TalkBack users on Android can trigger this action by pressing the
  /// volume up button.
  VoidCallback? get onIncrease => _onIncrease;
  VoidCallback? _onIncrease;
  set onIncrease(VoidCallback? handler) {
    if (_onIncrease == handler)
      return;
    final bool hadValue = _onIncrease != null;
    _onIncrease = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.decrease].
  ///
  /// This is a request to decrease the value represented by the widget. For
  /// example, this action might be recognized by a slider control.
  ///
  /// VoiceOver users on iOS can trigger this action by swiping down with one
  /// finger. TalkBack users on Android can trigger this action by pressing the
  /// volume down button.
  VoidCallback? get onDecrease => _onDecrease;
  VoidCallback? _onDecrease;
  set onDecrease(VoidCallback? handler) {
    if (_onDecrease == handler)
      return;
    final bool hadValue = _onDecrease != null;
    _onDecrease = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.copy].
  ///
  /// This is a request to copy the current selection to the clipboard.
  ///
  /// TalkBack users on Android can trigger this action from the local context
  /// menu of a text field, for example.
  VoidCallback? get onCopy => _onCopy;
  VoidCallback? _onCopy;
  set onCopy(VoidCallback? handler) {
    if (_onCopy == handler)
      return;
    final bool hadValue = _onCopy != null;
    _onCopy = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.cut].
  ///
  /// This is a request to cut the current selection and place it in the
  /// clipboard.
  ///
  /// TalkBack users on Android can trigger this action from the local context
  /// menu of a text field, for example.
  VoidCallback? get onCut => _onCut;
  VoidCallback? _onCut;
  set onCut(VoidCallback? handler) {
    if (_onCut == handler)
      return;
    final bool hadValue = _onCut != null;
    _onCut = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.paste].
  ///
  /// This is a request to paste the current content of the clipboard.
  ///
  /// TalkBack users on Android can trigger this action from the local context
  /// menu of a text field, for example.
  VoidCallback? get onPaste => _onPaste;
  VoidCallback? _onPaste;
  set onPaste(VoidCallback? handler) {
    if (_onPaste == handler)
      return;
    final bool hadValue = _onPaste != null;
    _onPaste = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.moveCursorForwardByCharacter].
  ///
  /// This handler is invoked when the user wants to move the cursor in a
  /// text field forward by one character.
  ///
  /// TalkBack users can trigger this by pressing the volume up key while the
  /// input focus is in a text field.
  MoveCursorHandler? get onMoveCursorForwardByCharacter => _onMoveCursorForwardByCharacter;
  MoveCursorHandler? _onMoveCursorForwardByCharacter;
  set onMoveCursorForwardByCharacter(MoveCursorHandler? handler) {
    if (_onMoveCursorForwardByCharacter == handler)
      return;
    final bool hadValue = _onMoveCursorForwardByCharacter != null;
    _onMoveCursorForwardByCharacter = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.moveCursorBackwardByCharacter].
  ///
  /// This handler is invoked when the user wants to move the cursor in a
  /// text field backward by one character.
  ///
  /// TalkBack users can trigger this by pressing the volume down key while the
  /// input focus is in a text field.
  MoveCursorHandler? get onMoveCursorBackwardByCharacter => _onMoveCursorBackwardByCharacter;
  MoveCursorHandler? _onMoveCursorBackwardByCharacter;
  set onMoveCursorBackwardByCharacter(MoveCursorHandler? handler) {
    if (_onMoveCursorBackwardByCharacter == handler)
      return;
    final bool hadValue = _onMoveCursorBackwardByCharacter != null;
    _onMoveCursorBackwardByCharacter = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.moveCursorForwardByWord].
  ///
  /// This handler is invoked when the user wants to move the cursor in a
  /// text field backward by one character.
  ///
  /// TalkBack users can trigger this by pressing the volume down key while the
  /// input focus is in a text field.
  MoveCursorHandler? get onMoveCursorForwardByWord => _onMoveCursorForwardByWord;
  MoveCursorHandler? _onMoveCursorForwardByWord;
  set onMoveCursorForwardByWord(MoveCursorHandler? handler) {
    if (_onMoveCursorForwardByWord == handler)
      return;
    final bool hadValue = _onMoveCursorForwardByWord != null;
    _onMoveCursorForwardByWord = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.moveCursorBackwardByWord].
  ///
  /// This handler is invoked when the user wants to move the cursor in a
  /// text field backward by one character.
  ///
  /// TalkBack users can trigger this by pressing the volume down key while the
  /// input focus is in a text field.
  MoveCursorHandler? get onMoveCursorBackwardByWord => _onMoveCursorBackwardByWord;
  MoveCursorHandler? _onMoveCursorBackwardByWord;
  set onMoveCursorBackwardByWord(MoveCursorHandler? handler) {
    if (_onMoveCursorBackwardByWord == handler)
      return;
    final bool hadValue = _onMoveCursorBackwardByWord != null;
    _onMoveCursorBackwardByWord = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.setSelection].
  ///
  /// This handler is invoked when the user either wants to change the currently
  /// selected text in a text field or change the position of the cursor.
  ///
  /// TalkBack users can trigger this handler by selecting "Move cursor to
  /// beginning/end" or "Select all" from the local context menu.
  SetSelectionHandler? get onSetSelection => _onSetSelection;
  SetSelectionHandler? _onSetSelection;
  set onSetSelection(SetSelectionHandler? handler) {
    if (_onSetSelection == handler)
      return;
    final bool hadValue = _onSetSelection != null;
    _onSetSelection = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.didGainAccessibilityFocus].
  ///
  /// This handler is invoked when the node annotated with this handler gains
  /// the accessibility focus. The accessibility focus is the
  /// green (on Android with TalkBack) or black (on iOS with VoiceOver)
  /// rectangle shown on screen to indicate what element an accessibility
  /// user is currently interacting with.
  ///
  /// The accessibility focus is different from the input focus. The input focus
  /// is usually held by the element that currently responds to keyboard inputs.
  /// Accessibility focus and input focus can be held by two different nodes!
  ///
  /// See also:
  ///
  ///  * [onDidLoseAccessibilityFocus], which is invoked when the accessibility
  ///    focus is removed from the node.
  ///  * [FocusNode], [FocusScope], [FocusManager], which manage the input focus.
  VoidCallback? get onDidGainAccessibilityFocus => _onDidGainAccessibilityFocus;
  VoidCallback? _onDidGainAccessibilityFocus;
  set onDidGainAccessibilityFocus(VoidCallback? handler) {
    if (_onDidGainAccessibilityFocus == handler)
      return;
    final bool hadValue = _onDidGainAccessibilityFocus != null;
    _onDidGainAccessibilityFocus = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handler for [SemanticsAction.didLoseAccessibilityFocus].
  ///
  /// This handler is invoked when the node annotated with this handler
  /// loses the accessibility focus. The accessibility focus is
  /// the green (on Android with TalkBack) or black (on iOS with VoiceOver)
  /// rectangle shown on screen to indicate what element an accessibility
  /// user is currently interacting with.
  ///
  /// The accessibility focus is different from the input focus. The input focus
  /// is usually held by the element that currently responds to keyboard inputs.
  /// Accessibility focus and input focus can be held by two different nodes!
  ///
  /// See also:
  ///
  ///  * [onDidGainAccessibilityFocus], which is invoked when the node gains
  ///    accessibility focus.
  ///  * [FocusNode], [FocusScope], [FocusManager], which manage the input focus.
  VoidCallback? get onDidLoseAccessibilityFocus => _onDidLoseAccessibilityFocus;
  VoidCallback? _onDidLoseAccessibilityFocus;
  set onDidLoseAccessibilityFocus(VoidCallback? handler) {
    if (_onDidLoseAccessibilityFocus == handler)
      return;
    final bool hadValue = _onDidLoseAccessibilityFocus != null;
    _onDidLoseAccessibilityFocus = handler;
    if ((handler != null) != hadValue)
      markNeedsSemanticsUpdate();
  }

  /// The handlers and supported [CustomSemanticsAction]s for this node.
  ///
  /// These handlers are called whenever the user performs the associated
  /// custom accessibility action from a special platform menu. Providing any
  /// custom actions here also adds [SemanticsAction.customAction] to the node.
  ///
  /// See also:
  ///
  ///  * [CustomSemanticsAction], for an explanation of custom actions.
  Map<CustomSemanticsAction, VoidCallback>? get customSemanticsActions => _customSemanticsActions;
  Map<CustomSemanticsAction, VoidCallback>? _customSemanticsActions;
  set customSemanticsActions(Map<CustomSemanticsAction, VoidCallback>? value) {
    if (_customSemanticsActions == value)
      return;
    _customSemanticsActions = value;
    markNeedsSemanticsUpdate();
  }

  @override
  void visitChildrenForSemantics(RenderObjectVisitor visitor) {
    if (excludeSemantics)
      return;
    super.visitChildrenForSemantics(visitor);
  }

  @override
  void describeSemanticsConfiguration(SemanticsConfiguration config) {
    super.describeSemanticsConfiguration(config);
    config.isSemanticBoundary = container;
    config.explicitChildNodes = explicitChildNodes;
    assert((scopesRoute == true && explicitChildNodes == true) || scopesRoute != true,
      'explicitChildNodes must be set to true if scopes route is true');
    assert(!(toggled == true && checked == true),
      'A semantics node cannot be toggled and checked at the same time');

    if (enabled != null)
      config.isEnabled = enabled;
    if (checked != null)
      config.isChecked = checked;
    if (toggled != null)
      config.isToggled = toggled;
    if (selected != null)
      config.isSelected = selected!;
    if (button != null)
      config.isButton = button!;
    if (link != null)
      config.isLink = link!;
    if (slider != null)
      config.isSlider = slider!;
    if (header != null)
      config.isHeader = header!;
    if (textField != null)
      config.isTextField = textField!;
    if (readOnly != null)
      config.isReadOnly = readOnly!;
    if (focusable != null)
      config.isFocusable = focusable!;
    if (focused != null)
      config.isFocused = focused!;
    if (inMutuallyExclusiveGroup != null)
      config.isInMutuallyExclusiveGroup = inMutuallyExclusiveGroup!;
    if (obscured != null)
      config.isObscured = obscured!;
    if (multiline != null)
      config.isMultiline = multiline!;
    if (hidden != null)
      config.isHidden = hidden!;
    if (image != null)
      config.isImage = image!;
    if (label != null)
      config.label = label!;
    if (value != null)
      config.value = value!;
    if (increasedValue != null)
      config.increasedValue = increasedValue!;
    if (decreasedValue != null)
      config.decreasedValue = decreasedValue!;
    if (hint != null)
      config.hint = hint!;
    if (hintOverrides != null && hintOverrides!.isNotEmpty)
      config.hintOverrides = hintOverrides;
    if (scopesRoute != null)
      config.scopesRoute = scopesRoute!;
    if (namesRoute != null)
      config.namesRoute = namesRoute!;
    if (liveRegion != null)
      config.liveRegion = liveRegion!;
    if (maxValueLength != null) {
      config.maxValueLength = maxValueLength;
    }
    if (currentValueLength != null) {
      config.currentValueLength = currentValueLength;
    }
    if (textDirection != null)
      config.textDirection = textDirection;
    if (sortKey != null)
      config.sortKey = sortKey;
    if (tagForChildren != null)
      config.addTagForChildren(tagForChildren!);
    // Registering _perform* as action handlers instead of the user provided
    // ones to ensure that changing a user provided handler from a non-null to
    // another non-null value doesn't require a semantics update.
    if (onTap != null)
      config.onTap = _performTap;
    if (onLongPress != null)
      config.onLongPress = _performLongPress;
    if (onDismiss != null)
      config.onDismiss = _performDismiss;
    if (onScrollLeft != null)
      config.onScrollLeft = _performScrollLeft;
    if (onScrollRight != null)
      config.onScrollRight = _performScrollRight;
    if (onScrollUp != null)
      config.onScrollUp = _performScrollUp;
    if (onScrollDown != null)
      config.onScrollDown = _performScrollDown;
    if (onIncrease != null)
      config.onIncrease = _performIncrease;
    if (onDecrease != null)
      config.onDecrease = _performDecrease;
    if (onCopy != null)
      config.onCopy = _performCopy;
    if (onCut != null)
      config.onCut = _performCut;
    if (onPaste != null)
      config.onPaste = _performPaste;
    if (onMoveCursorForwardByCharacter != null)
      config.onMoveCursorForwardByCharacter = _performMoveCursorForwardByCharacter;
    if (onMoveCursorBackwardByCharacter != null)
      config.onMoveCursorBackwardByCharacter = _performMoveCursorBackwardByCharacter;
    if (onMoveCursorForwardByWord != null)
      config.onMoveCursorForwardByWord = _performMoveCursorForwardByWord;
    if (onMoveCursorBackwardByWord != null)
      config.onMoveCursorBackwardByWord = _performMoveCursorBackwardByWord;
    if (onSetSelection != null)
      config.onSetSelection = _performSetSelection;
    if (onDidGainAccessibilityFocus != null)
      config.onDidGainAccessibilityFocus = _performDidGainAccessibilityFocus;
    if (onDidLoseAccessibilityFocus != null)
      config.onDidLoseAccessibilityFocus = _performDidLoseAccessibilityFocus;
    if (customSemanticsActions != null)
      config.customSemanticsActions = _customSemanticsActions!;
  }

  void _performTap() {
    if (onTap != null)
      onTap!();
  }

  void _performLongPress() {
    if (onLongPress != null)
      onLongPress!();
  }

  void _performDismiss() {
    if (onDismiss != null)
      onDismiss!();
  }

  void _performScrollLeft() {
    if (onScrollLeft != null)
      onScrollLeft!();
  }

  void _performScrollRight() {
    if (onScrollRight != null)
      onScrollRight!();
  }

  void _performScrollUp() {
    if (onScrollUp != null)
      onScrollUp!();
  }

  void _performScrollDown() {
    if (onScrollDown != null)
      onScrollDown!();
  }

  void _performIncrease() {
    if (onIncrease != null)
      onIncrease!();
  }

  void _performDecrease() {
    if (onDecrease != null)
      onDecrease!();
  }

  void _performCopy() {
    if (onCopy != null)
      onCopy!();
  }

  void _performCut() {
    if (onCut != null)
      onCut!();
  }

  void _performPaste() {
    if (onPaste != null)
      onPaste!();
  }

  void _performMoveCursorForwardByCharacter(bool extendSelection) {
    if (onMoveCursorForwardByCharacter != null)
      onMoveCursorForwardByCharacter!(extendSelection);
  }

  void _performMoveCursorBackwardByCharacter(bool extendSelection) {
    if (onMoveCursorBackwardByCharacter != null)
      onMoveCursorBackwardByCharacter!(extendSelection);
  }

  void _performMoveCursorForwardByWord(bool extendSelection) {
    if (onMoveCursorForwardByWord != null)
      onMoveCursorForwardByWord!(extendSelection);
  }

  void _performMoveCursorBackwardByWord(bool extendSelection) {
    if (onMoveCursorBackwardByWord != null)
      onMoveCursorBackwardByWord!(extendSelection);
  }

  void _performSetSelection(TextSelection selection) {
    if (onSetSelection != null)
      onSetSelection!(selection);
  }

  void _performDidGainAccessibilityFocus() {
    if (onDidGainAccessibilityFocus != null)
      onDidGainAccessibilityFocus!();
  }

  void _performDidLoseAccessibilityFocus() {
    if (onDidLoseAccessibilityFocus != null)
      onDidLoseAccessibilityFocus!();
  }
}

/// Causes the semantics of all earlier render objects below the same semantic
/// boundary to be dropped.
///
/// This is useful in a stack where an opaque mask should prevent interactions
/// with the render objects painted below the mask.
class RenderBlockSemantics extends RenderProxyBox {
  /// Create a render object that blocks semantics for nodes below it in paint
  /// order.
  RenderBlockSemantics({
    RenderBox? child,
    bool blocking = true,
  }) : _blocking = blocking,
       super(child);

  /// Whether this render object is blocking semantics of previously painted
  /// [RenderObject]s below a common semantics boundary from the semantic tree.
  bool get blocking => _blocking;
  bool _blocking;
  set blocking(bool value) {
    assert(value != null);
    if (value == _blocking)
      return;
    _blocking = value;
    markNeedsSemanticsUpdate();
  }

  @override
  void describeSemanticsConfiguration(SemanticsConfiguration config) {
    super.describeSemanticsConfiguration(config);
    config.isBlockingSemanticsOfPreviouslyPaintedNodes = blocking;
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<bool>('blocking', blocking));
  }
}

/// Causes the semantics of all descendants to be merged into this
/// node such that the entire subtree becomes a single leaf in the
/// semantics tree.
///
/// Useful for combining the semantics of multiple render objects that
/// form part of a single conceptual widget, e.g. a checkbox, a label,
/// and the gesture detector that goes with them.
class RenderMergeSemantics extends RenderProxyBox {
  /// Creates a render object that merges the semantics from its descendants.
  RenderMergeSemantics({ RenderBox? child }) : super(child);

  @override
  void describeSemanticsConfiguration(SemanticsConfiguration config) {
    super.describeSemanticsConfiguration(config);
    config
      ..isSemanticBoundary = true
      ..isMergingSemanticsOfDescendants = true;
  }
}

/// Excludes this subtree from the semantic tree.
///
/// When [excluding] is true, this render object (and its subtree) is excluded
/// from the semantic tree.
///
/// Useful e.g. for hiding text that is redundant with other text next
/// to it (e.g. text included only for the visual effect).
class RenderExcludeSemantics extends RenderProxyBox {
  /// Creates a render object that ignores the semantics of its subtree.
  RenderExcludeSemantics({
    RenderBox? child,
    bool excluding = true,
  }) : _excluding = excluding,
       super(child) {
    assert(_excluding != null);
  }

  /// Whether this render object is excluded from the semantic tree.
  bool get excluding => _excluding;
  bool _excluding;
  set excluding(bool value) {
    assert(value != null);
    if (value == _excluding)
      return;
    _excluding = value;
    markNeedsSemanticsUpdate();
  }

  @override
  void visitChildrenForSemantics(RenderObjectVisitor visitor) {
    if (excluding)
      return;
    super.visitChildrenForSemantics(visitor);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<bool>('excluding', excluding));
  }
}

/// A render objects that annotates semantics with an index.
///
/// Certain widgets will automatically provide a child index for building
/// semantics. For example, the [ScrollView] uses the index of the first
/// visible child semantics node to determine the
/// [SemanticsConfiguration.scrollIndex].
///
/// See also:
///
///  * [CustomScrollView], for an explanation of scroll semantics.
class RenderIndexedSemantics extends RenderProxyBox {
  /// Creates a render object that annotates the child semantics with an index.
  RenderIndexedSemantics({
    RenderBox? child,
    required int index,
  }) : assert(index != null),
       _index = index,
       super(child);

  /// The index used to annotated child semantics.
  int get index => _index;
  int _index;
  set index(int value) {
    if (value == index)
      return;
    _index = value;
    markNeedsSemanticsUpdate();
  }

  @override
  void describeSemanticsConfiguration(SemanticsConfiguration config) {
    super.describeSemanticsConfiguration(config);
    config.isSemanticBoundary = true;
    config.indexInParent = index;
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<int>('index', index));
  }
}

/// Provides an anchor for a [RenderFollowerLayer].
///
/// See also:
///
///  * [CompositedTransformTarget], the corresponding widget.
///  * [LeaderLayer], the layer that this render object creates.
class RenderLeaderLayer extends RenderProxyBox {
  /// Creates a render object that uses a [LeaderLayer].
  ///
  /// The [link] must not be null.
  RenderLeaderLayer({
    required LayerLink link,
    RenderBox? child,
  }) : assert(link != null),
       _link = link,
       super(child);

  /// The link object that connects this [RenderLeaderLayer] with one or more
  /// [RenderFollowerLayer]s.
  ///
  /// This property must not be null. The object must not be associated with
  /// another [RenderLeaderLayer] that is also being painted.
  LayerLink get link => _link;
  LayerLink _link;
  set link(LayerLink value) {
    assert(value != null);
    if (_link == value)
      return;
    _link.leaderSize = null;
    _link = value;
    if (_previousLayoutSize != null) {
      _link.leaderSize = _previousLayoutSize;
    }
    markNeedsPaint();
  }

  @override
  bool get alwaysNeedsCompositing => true;

  // The latest size of this [RenderBox], computed during the previous layout
  // pass. It should always be equal to [size], but can be accessed even when
  // [debugDoingThisResize] and [debugDoingThisLayout] are false.
  Size? _previousLayoutSize;

  @override
  void performLayout() {
    super.performLayout();
    _previousLayoutSize = size;
    link.leaderSize = size;
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (layer == null) {
      layer = LeaderLayer(link: link, offset: offset);
    } else {
      final LeaderLayer leaderLayer = layer! as LeaderLayer;
      leaderLayer
        ..link = link
        ..offset = offset;
    }
    context.pushLayer(layer!, super.paint, Offset.zero);
    assert(layer != null);
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<LayerLink>('link', link));
  }
}

/// Transform the child so that its origin is [offset] from the origin of the
/// [RenderLeaderLayer] with the same [LayerLink].
///
/// The [RenderLeaderLayer] in question must be earlier in the paint order.
///
/// Hit testing on descendants of this render object will only work if the
/// target position is within the box that this render object's parent considers
/// to be hittable.
///
/// See also:
///
///  * [CompositedTransformFollower], the corresponding widget.
///  * [FollowerLayer], the layer that this render object creates.
class RenderFollowerLayer extends RenderProxyBox {
  /// Creates a render object that uses a [FollowerLayer].
  ///
  /// The [link] and [offset] arguments must not be null.
  RenderFollowerLayer({
    required LayerLink link,
    bool showWhenUnlinked = true,
    Offset offset = Offset.zero,
    Alignment leaderAnchor = Alignment.topLeft,
    Alignment followerAnchor = Alignment.topLeft,
    RenderBox? child,
  }) : assert(link != null),
       assert(showWhenUnlinked != null),
       assert(offset != null),
       _link = link,
       _showWhenUnlinked = showWhenUnlinked,
       _offset = offset,
       _leaderAnchor = leaderAnchor,
       _followerAnchor = followerAnchor,
       super(child);

  /// The link object that connects this [RenderFollowerLayer] with a
  /// [RenderLeaderLayer] earlier in the paint order.
  LayerLink get link => _link;
  LayerLink _link;
  set link(LayerLink value) {
    assert(value != null);
    if (_link == value)
      return;
    _link = value;
    markNeedsPaint();
  }

  /// Whether to show the render object's contents when there is no
  /// corresponding [RenderLeaderLayer] with the same [link].
  ///
  /// When the render object is linked, the child is positioned such that it has
  /// the same global position as the linked [RenderLeaderLayer].
  ///
  /// When the render object is not linked, then: if [showWhenUnlinked] is true,
  /// the child is visible and not repositioned; if it is false, then child is
  /// hidden, and its hit testing is also disabled.
  bool get showWhenUnlinked => _showWhenUnlinked;
  bool _showWhenUnlinked;
  set showWhenUnlinked(bool value) {
    assert(value != null);
    if (_showWhenUnlinked == value)
      return;
    _showWhenUnlinked = value;
    markNeedsPaint();
  }

  /// The offset to apply to the origin of the linked [RenderLeaderLayer] to
  /// obtain this render object's origin.
  Offset get offset => _offset;
  Offset _offset;
  set offset(Offset value) {
    assert(value != null);
    if (_offset == value)
      return;
    _offset = value;
    markNeedsPaint();
  }

  /// The anchor point on the linked [RenderLeaderLayer] that [followerAnchor]
  /// will line up with.
  ///
  /// {@template flutter.rendering.RenderFollowerLayer.leaderAnchor}
  /// For example, when [leaderAnchor] and [followerAnchor] are both
  /// [Alignment.topLeft], this [RenderFollowerLayer] will be top left aligned
  /// with the linked [RenderLeaderLayer]. When [leaderAnchor] is
  /// [Alignment.bottomLeft] and [followerAnchor] is [Alignment.topLeft], this
  /// [RenderFollowerLayer] will be left aligned with the linked
  /// [RenderLeaderLayer], and its top edge will line up with the
  /// [RenderLeaderLayer]'s bottom edge.
  /// {@endtemplate}
  ///
  /// Defaults to [Alignment.topLeft].
  Alignment get leaderAnchor => _leaderAnchor;
  Alignment _leaderAnchor;
  set leaderAnchor(Alignment value) {
    assert(value != null);
    if (_leaderAnchor == value)
      return;
    _leaderAnchor = value;
    markNeedsPaint();
  }

  /// The anchor point on this [RenderFollowerLayer] that will line up with
  /// [followerAnchor] on the linked [RenderLeaderLayer].
  ///
  /// {@macro flutter.rendering.RenderFollowerLayer.leaderAnchor}
  ///
  /// Defaults to [Alignment.topLeft].
  Alignment get followerAnchor => _followerAnchor;
  Alignment _followerAnchor;
  set followerAnchor(Alignment value) {
    assert(value != null);
    if (_followerAnchor == value)
      return;
    _followerAnchor = value;
    markNeedsPaint();
  }

  @override
  void detach() {
    layer = null;
    super.detach();
  }

  @override
  bool get alwaysNeedsCompositing => true;

  /// The layer we created when we were last painted.
  @override
  FollowerLayer? get layer => super.layer as FollowerLayer?;

  /// Return the transform that was used in the last composition phase, if any.
  ///
  /// If the [FollowerLayer] has not yet been created, was never composited, or
  /// was unable to determine the transform (see
  /// [FollowerLayer.getLastTransform]), this returns the identity matrix (see
  /// [new Matrix4.identity].
  Matrix4 getCurrentTransform() {
    return layer?.getLastTransform() ?? Matrix4.identity();
  }

  @override
  bool hitTest(BoxHitTestResult result, { required Offset position }) {
    // Disables the hit testing if this render object is hidden.
    if (link.leader == null && !showWhenUnlinked)
      return false;
    // RenderFollowerLayer objects don't check if they are
    // themselves hit, because it's confusing to think about
    // how the untransformed size and the child's transformed
    // position interact.
    return hitTestChildren(result, position: position);
  }

  @override
  bool hitTestChildren(BoxHitTestResult result, { required Offset position }) {
    return result.addWithPaintTransform(
      transform: getCurrentTransform(),
      position: position,
      hitTest: (BoxHitTestResult result, Offset? position) {
        return super.hitTestChildren(result, position: position!);
      },
    );
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    final Size? leaderSize = link.leaderSize;
    assert(
      link.leaderSize != null || (link.leader == null || leaderAnchor == Alignment.topLeft),
      '$link: layer is linked to ${link.leader} but a valid leaderSize is not set. '
      'leaderSize is required when leaderAnchor is not Alignment.topLeft'
      '(current value is $leaderAnchor).',
    );
    final Offset effectiveLinkedOffset = leaderSize == null
      ? this.offset
      : leaderAnchor.alongSize(leaderSize) - followerAnchor.alongSize(size) + this.offset;
    assert(showWhenUnlinked != null);
    if (layer == null) {
      layer = FollowerLayer(
        link: link,
        showWhenUnlinked: showWhenUnlinked,
        linkedOffset: effectiveLinkedOffset,
        unlinkedOffset: offset,
      );
    } else {
      layer
        ?..link = link
        ..showWhenUnlinked = showWhenUnlinked
        ..linkedOffset = effectiveLinkedOffset
        ..unlinkedOffset = offset;
    }
    context.pushLayer(
      layer!,
      super.paint,
      Offset.zero,
      childPaintBounds: const Rect.fromLTRB(
        // We don't know where we'll end up, so we have no idea what our cull rect should be.
        double.negativeInfinity,
        double.negativeInfinity,
        double.infinity,
        double.infinity,
      ),
    );
  }

  @override
  void applyPaintTransform(RenderBox child, Matrix4 transform) {
    transform.multiply(getCurrentTransform());
  }

  @override
  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
    super.debugFillProperties(properties);
    properties.add(DiagnosticsProperty<LayerLink>('link', link));
    properties.add(DiagnosticsProperty<bool>('showWhenUnlinked', showWhenUnlinked));
    properties.add(DiagnosticsProperty<Offset>('offset', offset));
    properties.add(TransformProperty('current transform matrix', getCurrentTransform()));
  }
}

/// Render object which inserts an [AnnotatedRegionLayer] into the layer tree.
///
/// See also:
///
///  * [Layer.find], for an example of how this value is retrieved.
///  * [AnnotatedRegionLayer], the layer this render object creates.
class RenderAnnotatedRegion<T extends Object> extends RenderProxyBox {

  /// Creates a new [RenderAnnotatedRegion] to insert [value] into the
  /// layer tree.
  ///
  /// If [sized] is true, the layer is provided with the size of this render
  /// object to clip the results of [Layer.find].
  ///
  /// Neither [value] nor [sized] can be null.
  RenderAnnotatedRegion({
    required T value,
    required bool sized,
    RenderBox? child,
  }) : assert(value != null),
       assert(sized != null),
       _value = value,
       _sized = sized,
       super(child);

  /// A value which can be retrieved using [Layer.find].
  T get value => _value;
  T _value;
  set value (T newValue) {
    if (_value == newValue)
      return;
    _value = newValue;
    markNeedsPaint();
  }

  /// Whether the render object will pass its [size] to the [AnnotatedRegionLayer].
  bool get sized => _sized;
  bool _sized;
  set sized(bool value) {
    if (_sized == value)
      return;
    _sized = value;
    markNeedsPaint();
  }

  @override
  final bool alwaysNeedsCompositing = true;

  @override
  void paint(PaintingContext context, Offset offset) {
    // Annotated region layers are not retained because they do not create engine layers.
    final AnnotatedRegionLayer<T> layer = AnnotatedRegionLayer<T>(
      value,
      size: sized ? size : null,
      offset: sized ? offset : null,
    );
    context.pushLayer(layer, super.paint, offset);
  }
}
