proxy_sliver.dart

// 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 Color;

import 'package:flutter/animation.dart';
import 'package:flutter/foundation.dart';
import 'package:vector_math/vector_math_64.dart';

import 'layer.dart';
import 'object.dart';
import 'proxy_box.dart';
import 'sliver.dart';

/// A base class for sliver render objects that resemble their children.
///
/// A proxy sliver 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
/// sliver protocol. For example, a proxy sliver determines its geometry by
/// asking its sliver child to layout with the same constraints and then
/// matching the geometry.
///
/// A proxy sliver isn't useful on its own because you might as well just
/// replace the proxy sliver with its child. However, RenderProxySliver is a
/// useful base class for render objects that wish to mimic most, but not all,
/// of the properties of their sliver child.
///
/// See also:
///
///  * [RenderProxyBox], a base class for render boxes that resemble their
///    children.
abstract class RenderProxySliver extends RenderSliver with RenderObjectWithChildMixin<RenderSliver> {
  /// Creates a proxy render sliver.
  ///
  /// Proxy render slivers aren't created directly because they simply proxy
  /// the render sliver protocol to their sliver [child]. Instead, use one of
  /// the subclasses.
  RenderProxySliver([RenderSliver? child]) {
    this.child = child;
  }

  @override
  void setupParentData(RenderObject child) {
    if (child.parentData is! SliverPhysicalParentData)
      child.parentData = SliverPhysicalParentData();
  }

  @override
  void performLayout() {
    assert(child != null);
    child!.layout(constraints, parentUsesSize: true);
    geometry = child!.geometry;
  }

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

  @override
  bool hitTestChildren(SliverHitTestResult result, {required double mainAxisPosition, required double crossAxisPosition}) {
    return child != null
      && child!.geometry!.hitTestExtent > 0
      && child!.hitTest(
        result,
        mainAxisPosition: mainAxisPosition,
        crossAxisPosition: crossAxisPosition,
      );
  }

  @override
  double childMainAxisPosition(RenderSliver child) {
    assert(child != null);
    assert(child == this.child);
    return 0.0;
  }

  @override
  void applyPaintTransform(RenderObject child, Matrix4 transform) {
    assert(child != null);
    final SliverPhysicalParentData childParentData = child.parentData! as SliverPhysicalParentData;
    childParentData.applyPaintTransform(transform);
  }
}

/// Makes its sliver child partially transparent.
///
/// This class paints its sliver child into an intermediate buffer and then
/// blends the sliver 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 sliver child into an intermediate
/// buffer. For the value 0.0, the sliver child is simply not painted at all.
/// For the value 1.0, the sliver child is painted immediately without an
/// intermediate buffer.
class RenderSliverOpacity extends RenderProxySliver {
  /// Creates a partially transparent render object.
  ///
  /// The [opacity] argument must be between 0.0 and 1.0, inclusive.
  RenderSliverOpacity({
    double opacity = 1.0,
    bool alwaysIncludeSemantics = false,
    RenderSliver? sliver,
  }) : assert(opacity != null && opacity >= 0.0 && opacity <= 1.0),
       assert(alwaysIncludeSemantics != null),
       _opacity = opacity,
       _alwaysIncludeSemantics = alwaysIncludeSemantics,
       _alpha = ui.Color.getAlphaFromOpacity(opacity) {
    child = sliver;
  }

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

  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 && child!.geometry!.visible) {
      if (_alpha == 0) {
        // No need to keep the layer. We'll create a new one if necessary.
        layer = null;
        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'));
  }
}

/// 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 sliver
/// 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].
class RenderSliverIgnorePointer extends RenderProxySliver {
  /// 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.
  RenderSliverIgnorePointer({
    RenderSliver? sliver,
    bool ignoring = true,
    bool? ignoringSemantics,
  }) : assert(ignoring != null),
       _ignoring = ignoring,
       _ignoringSemantics = ignoringSemantics {
    child = sliver;
  }

  /// 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(SliverHitTestResult result, {required double mainAxisPosition, required double crossAxisPosition}) {
    return !ignoring
      && super.hitTest(
        result,
        mainAxisPosition: mainAxisPosition,
        crossAxisPosition: crossAxisPosition,
      );
  }

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

  /// Whether the sliver child is hidden from the rest of the tree.
  ///
  /// If true, the sliver child is laid out as if it was in the tree, but
  /// without painting anything, without making the sliver child available for
  /// hit testing, and without taking any room in the parent.
  ///
  /// If false, the sliver 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
  void performLayout() {
    assert(child != null);
    child!.layout(constraints, parentUsesSize: true);
    if (!offstage)
      geometry = child!.geometry;
    else
      geometry = SliverGeometry.zero;
  }

  @override
  bool hitTest(SliverHitTestResult result, {required double mainAxisPosition, required double crossAxisPosition}) {
    return !offstage && super.hitTest(
      result,
      mainAxisPosition: mainAxisPosition,
      crossAxisPosition: crossAxisPosition,
    );
  }

  @override
  bool hitTestChildren(SliverHitTestResult result, {required double mainAxisPosition, required double crossAxisPosition}) {
    return !offstage
      && child != null
      && child!.geometry!.hitTestExtent > 0
      && child!.hitTest(
        result,
        mainAxisPosition: mainAxisPosition,
        crossAxisPosition: crossAxisPosition,
      );
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    if (offstage)
      return;
    context.paintChild(child!, 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,
      ),
    ];
  }
}

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