interactive_viewer.dart 53.7 KB
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// 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:math' as math;

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import 'package:flutter/foundation.dart' show clampDouble;
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import 'package:flutter/gestures.dart';
import 'package:flutter/physics.dart';
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import 'package:vector_math/vector_math_64.dart' show Matrix4, Quad, Vector3;
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import 'basic.dart';
import 'framework.dart';
import 'gesture_detector.dart';
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import 'layout_builder.dart';
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import 'ticker_provider.dart';

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// Examples can assume:
// late BuildContext context;
// late Offset? _childWasTappedAt;
// late TransformationController _transformationController;
// Widget child = const Placeholder();

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/// A signature for widget builders that take a [Quad] of the current viewport.
///
/// See also:
///
///   * [InteractiveViewer.builder], whose builder is of this type.
///   * [WidgetBuilder], which is similar, but takes no viewport.
typedef InteractiveViewerWidgetBuilder = Widget Function(BuildContext context, Quad viewport);

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/// A widget that enables pan and zoom interactions with its child.
///
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/// {@youtube 560 315 https://www.youtube.com/watch?v=zrn7V3bMJvg}
///
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/// The user can transform the child by dragging to pan or pinching to zoom.
///
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/// By default, InteractiveViewer clips its child using [Clip.hardEdge].
/// To prevent this behavior, consider setting [clipBehavior] to [Clip.none].
/// When [clipBehavior] is [Clip.none], InteractiveViewer may draw outside of
/// its original area of the screen, such as when a child is zoomed in and
/// increases in size. However, it will not receive gestures outside of its original area.
/// To prevent dead areas where InteractiveViewer does not receive gestures,
/// don't set [clipBehavior] or be sure that the InteractiveViewer widget is the
/// size of the area that should be interactive.
///
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/// The [child] must not be null.
///
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/// See also:
///   * The [Flutter Gallery's transformations demo](https://github.com/flutter/gallery/blob/master/lib/demos/reference/transformations_demo.dart),
///     which includes the use of InteractiveViewer.
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///   * The [flutter-go demo](https://github.com/justinmc/flutter-go), which includes robust positioning of an InteractiveViewer child
///     that works for all screen sizes and child sizes.
///   * The [Lazy Flutter Performance Session](https://www.youtube.com/watch?v=qax_nOpgz7E), which includes the use of an InteractiveViewer to
///     performantly view subsets of a large set of widgets using the builder constructor.
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///
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/// {@tool dartpad}
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/// This example shows a simple Container that can be panned and zoomed.
///
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/// ** See code in examples/api/lib/widgets/interactive_viewer/interactive_viewer.0.dart **
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/// {@end-tool}
@immutable
class InteractiveViewer extends StatefulWidget {
  /// Create an InteractiveViewer.
  ///
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  /// The [child] parameter must not be null.
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  InteractiveViewer({
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    super.key,
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    this.clipBehavior = Clip.hardEdge,
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    @Deprecated(
      'Use panAxis instead. '
      'This feature was deprecated after v3.3.0-0.5.pre.',
    )
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    this.alignPanAxis = false,
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    this.panAxis = PanAxis.free,
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    this.boundaryMargin = EdgeInsets.zero,
    this.constrained = true,
    // These default scale values were eyeballed as reasonable limits for common
    // use cases.
    this.maxScale = 2.5,
    this.minScale = 0.8,
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    this.interactionEndFrictionCoefficient = _kDrag,
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    this.onInteractionEnd,
    this.onInteractionStart,
    this.onInteractionUpdate,
    this.panEnabled = true,
    this.scaleEnabled = true,
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    this.scaleFactor = kDefaultMouseScrollToScaleFactor,
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    this.transformationController,
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    this.alignment,
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    this.trackpadScrollCausesScale = false,
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    required Widget this.child,
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  }) : assert(minScale > 0),
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       assert(interactionEndFrictionCoefficient > 0),
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       assert(minScale.isFinite),
       assert(maxScale > 0),
       assert(!maxScale.isNaN),
       assert(maxScale >= minScale),
       // boundaryMargin must be either fully infinite or fully finite, but not
       // a mix of both.
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       assert(
         (boundaryMargin.horizontal.isInfinite
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           && boundaryMargin.vertical.isInfinite) || (boundaryMargin.top.isFinite
           && boundaryMargin.right.isFinite && boundaryMargin.bottom.isFinite
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           && boundaryMargin.left.isFinite),
       ),
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       builder = null;
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  /// Creates an InteractiveViewer for a child that is created on demand.
  ///
  /// Can be used to render a child that changes in response to the current
  /// transformation.
  ///
  /// The [builder] parameter must not be null. See its docs for an example of
  /// using it to optimize a large child.
  InteractiveViewer.builder({
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    super.key,
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    this.clipBehavior = Clip.hardEdge,
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    @Deprecated(
      'Use panAxis instead. '
      'This feature was deprecated after v3.3.0-0.5.pre.',
    )
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    this.alignPanAxis = false,
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    this.panAxis = PanAxis.free,
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    this.boundaryMargin = EdgeInsets.zero,
    // These default scale values were eyeballed as reasonable limits for common
    // use cases.
    this.maxScale = 2.5,
    this.minScale = 0.8,
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    this.interactionEndFrictionCoefficient = _kDrag,
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    this.onInteractionEnd,
    this.onInteractionStart,
    this.onInteractionUpdate,
    this.panEnabled = true,
    this.scaleEnabled = true,
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    this.scaleFactor = 200.0,
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    this.transformationController,
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    this.alignment,
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    this.trackpadScrollCausesScale = false,
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    required InteractiveViewerWidgetBuilder this.builder,
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  }) : assert(minScale > 0),
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       assert(interactionEndFrictionCoefficient > 0),
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       assert(minScale.isFinite),
       assert(maxScale > 0),
       assert(!maxScale.isNaN),
       assert(maxScale >= minScale),
       // boundaryMargin must be either fully infinite or fully finite, but not
       // a mix of both.
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       assert(
         (boundaryMargin.horizontal.isInfinite && boundaryMargin.vertical.isInfinite) ||
             (boundaryMargin.top.isFinite &&
                 boundaryMargin.right.isFinite &&
                 boundaryMargin.bottom.isFinite &&
                 boundaryMargin.left.isFinite),
       ),
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       constrained = false,
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       child = null;
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  /// The alignment of the child's origin, relative to the size of the box.
  final Alignment? alignment;

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  /// If set to [Clip.none], the child may extend beyond the size of the InteractiveViewer,
  /// but it will not receive gestures in these areas.
  /// Be sure that the InteractiveViewer is the desired size when using [Clip.none].
  ///
  /// Defaults to [Clip.hardEdge].
  final Clip clipBehavior;

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  /// This property is deprecated, please use [panAxis] instead.
  ///
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  /// If true, panning is only allowed in the direction of the horizontal axis
  /// or the vertical axis.
  ///
  /// In other words, when this is true, diagonal panning is not allowed. A
  /// single gesture begun along one axis cannot also cause panning along the
  /// other axis without stopping and beginning a new gesture. This is a common
  /// pattern in tables where data is displayed in columns and rows.
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  ///
  /// See also:
  ///  * [constrained], which has an example of creating a table that uses
  ///    alignPanAxis.
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  @Deprecated(
    'Use panAxis instead. '
    'This feature was deprecated after v3.3.0-0.5.pre.',
  )
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  final bool alignPanAxis;

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  /// When set to [PanAxis.aligned], panning is only allowed in the horizontal
  /// axis or the vertical axis, diagonal panning is not allowed.
  ///
  /// When set to [PanAxis.vertical] or [PanAxis.horizontal] panning is only
  /// allowed in the specified axis. For example, if set to [PanAxis.vertical],
  /// panning will only be allowed in the vertical axis. And if set to [PanAxis.horizontal],
  /// panning will only be allowed in the horizontal axis.
  ///
  /// When set to [PanAxis.free] panning is allowed in all directions.
  ///
  /// Defaults to [PanAxis.free].
  final PanAxis panAxis;

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  /// A margin for the visible boundaries of the child.
  ///
  /// Any transformation that results in the viewport being able to view outside
  /// of the boundaries will be stopped at the boundary. The boundaries do not
  /// rotate with the rest of the scene, so they are always aligned with the
  /// viewport.
  ///
  /// To produce no boundaries at all, pass infinite [EdgeInsets], such as
  /// `EdgeInsets.all(double.infinity)`.
  ///
  /// No edge can be NaN.
  ///
  /// Defaults to [EdgeInsets.zero], which results in boundaries that are the
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  /// exact same size and position as the [child].
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  final EdgeInsets boundaryMargin;

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  /// Builds the child of this widget.
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  ///
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  /// Passed with the [InteractiveViewer.builder] constructor. Otherwise, the
  /// [child] parameter must be passed directly, and this is null.
  ///
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  /// {@tool dartpad}
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  /// This example shows how to use builder to create a [Table] whose cell
  /// contents are only built when they are visible. Built and remove cells are
  /// logged in the console for illustration.
  ///
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  /// ** See code in examples/api/lib/widgets/interactive_viewer/interactive_viewer.builder.0.dart **
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  /// {@end-tool}
  ///
  /// See also:
  ///
  ///   * [ListView.builder], which follows a similar pattern.
  final InteractiveViewerWidgetBuilder? builder;

  /// The child [Widget] that is transformed by InteractiveViewer.
  ///
  /// If the [InteractiveViewer.builder] constructor is used, then this will be
  /// null, otherwise it is required.
  final Widget? child;
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  /// Whether the normal size constraints at this point in the widget tree are
  /// applied to the child.
  ///
  /// If set to false, then the child will be given infinite constraints. This
  /// is often useful when a child should be bigger than the InteractiveViewer.
  ///
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  /// For example, for a child which is bigger than the viewport but can be
  /// panned to reveal parts that were initially offscreen, [constrained] must
  /// be set to false to allow it to size itself properly. If [constrained] is
  /// true and the child can only size itself to the viewport, then areas
  /// initially outside of the viewport will not be able to receive user
  /// interaction events. If experiencing regions of the child that are not
  /// receptive to user gestures, make sure [constrained] is false and the child
  /// is sized properly.
  ///
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  /// Defaults to true.
  ///
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  /// {@tool dartpad}
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  /// This example shows how to create a pannable table. Because the table is
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  /// larger than the entire screen, setting [constrained] to false is necessary
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  /// to allow it to be drawn to its full size. The parts of the table that
  /// exceed the screen size can then be panned into view.
  ///
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  /// ** See code in examples/api/lib/widgets/interactive_viewer/interactive_viewer.constrained.0.dart **
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  /// {@end-tool}
  final bool constrained;

  /// If false, the user will be prevented from panning.
  ///
  /// Defaults to true.
  ///
  /// See also:
  ///
  ///   * [scaleEnabled], which is similar but for scale.
  final bool panEnabled;

  /// If false, the user will be prevented from scaling.
  ///
  /// Defaults to true.
  ///
  /// See also:
  ///
  ///   * [panEnabled], which is similar but for panning.
  final bool scaleEnabled;

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  /// {@macro flutter.gestures.scale.trackpadScrollCausesScale}
  final bool trackpadScrollCausesScale;

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  /// Determines the amount of scale to be performed per pointer scroll.
  ///
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  /// Defaults to [kDefaultMouseScrollToScaleFactor].
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  ///
  /// Increasing this value above the default causes scaling to feel slower,
  /// while decreasing it causes scaling to feel faster.
  ///
  /// The amount of scale is calculated as the exponential function of the
  /// [PointerScrollEvent.scrollDelta] to [scaleFactor] ratio. In the Flutter
  /// engine, the mousewheel [PointerScrollEvent.scrollDelta] is hardcoded to 20
  /// per scroll, while a trackpad scroll can be any amount.
  ///
  /// Affects only pointer device scrolling, not pinch to zoom.
  final double scaleFactor;

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  /// The maximum allowed scale.
  ///
  /// The scale will be clamped between this and [minScale] inclusively.
  ///
  /// Defaults to 2.5.
  ///
  /// Cannot be null, and must be greater than zero and greater than minScale.
  final double maxScale;

  /// The minimum allowed scale.
  ///
  /// The scale will be clamped between this and [maxScale] inclusively.
  ///
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  /// Scale is also affected by [boundaryMargin]. If the scale would result in
  /// viewing beyond the boundary, then it will not be allowed. By default,
  /// boundaryMargin is EdgeInsets.zero, so scaling below 1.0 will not be
  /// allowed in most cases without first increasing the boundaryMargin.
  ///
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  /// Defaults to 0.8.
  ///
  /// Cannot be null, and must be a finite number greater than zero and less
  /// than maxScale.
  final double minScale;

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  /// Changes the deceleration behavior after a gesture.
  ///
  /// Defaults to 0.0000135.
  ///
  /// Cannot be null, and must be a finite number greater than zero.
  final double interactionEndFrictionCoefficient;

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  /// Called when the user ends a pan or scale gesture on the widget.
  ///
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  /// At the time this is called, the [TransformationController] will have
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  /// already been updated to reflect the change caused by the interaction,
  /// though a pan may cause an inertia animation after this is called as well.
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  ///
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  /// {@template flutter.widgets.InteractiveViewer.onInteractionEnd}
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  /// Will be called even if the interaction is disabled with [panEnabled] or
  /// [scaleEnabled] for both touch gestures and mouse interactions.
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  ///
  /// A [GestureDetector] wrapping the InteractiveViewer will not respond to
  /// [GestureDetector.onScaleStart], [GestureDetector.onScaleUpdate], and
  /// [GestureDetector.onScaleEnd]. Use [onInteractionStart],
  /// [onInteractionUpdate], and [onInteractionEnd] to respond to those
  /// gestures.
  /// {@endtemplate}
  ///
  /// See also:
  ///
  ///  * [onInteractionStart], which handles the start of the same interaction.
  ///  * [onInteractionUpdate], which handles an update to the same interaction.
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  final GestureScaleEndCallback? onInteractionEnd;
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  /// Called when the user begins a pan or scale gesture on the widget.
  ///
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  /// At the time this is called, the [TransformationController] will not have
  /// changed due to this interaction.
  ///
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  /// {@macro flutter.widgets.InteractiveViewer.onInteractionEnd}
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  ///
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  /// The coordinates provided in the details' `focalPoint` and
  /// `localFocalPoint` are normal Flutter event coordinates, not
  /// InteractiveViewer scene coordinates. See
  /// [TransformationController.toScene] for how to convert these coordinates to
  /// scene coordinates relative to the child.
  ///
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  /// See also:
  ///
  ///  * [onInteractionUpdate], which handles an update to the same interaction.
  ///  * [onInteractionEnd], which handles the end of the same interaction.
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  final GestureScaleStartCallback? onInteractionStart;
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  /// Called when the user updates a pan or scale gesture on the widget.
  ///
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  /// At the time this is called, the [TransformationController] will have
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  /// already been updated to reflect the change caused by the interaction, if
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  /// the interaction caused the matrix to change.
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  ///
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  /// {@macro flutter.widgets.InteractiveViewer.onInteractionEnd}
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  ///
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  /// The coordinates provided in the details' `focalPoint` and
  /// `localFocalPoint` are normal Flutter event coordinates, not
  /// InteractiveViewer scene coordinates. See
  /// [TransformationController.toScene] for how to convert these coordinates to
  /// scene coordinates relative to the child.
  ///
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  /// See also:
  ///
  ///  * [onInteractionStart], which handles the start of the same interaction.
  ///  * [onInteractionEnd], which handles the end of the same interaction.
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  final GestureScaleUpdateCallback? onInteractionUpdate;
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  /// A [TransformationController] for the transformation performed on the
  /// child.
  ///
  /// Whenever the child is transformed, the [Matrix4] value is updated and all
  /// listeners are notified. If the value is set, InteractiveViewer will update
  /// to respect the new value.
  ///
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  /// {@tool dartpad}
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  /// This example shows how transformationController can be used to animate the
  /// transformation back to its starting position.
  ///
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  /// ** See code in examples/api/lib/widgets/interactive_viewer/interactive_viewer.transformation_controller.0.dart **
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  /// {@end-tool}
  ///
  /// See also:
  ///
  ///  * [ValueNotifier], the parent class of TransformationController.
  ///  * [TextEditingController] for an example of another similar pattern.
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  final TransformationController? transformationController;
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  // Used as the coefficient of friction in the inertial translation animation.
  // This value was eyeballed to give a feel similar to Google Photos.
  static const double _kDrag = 0.0000135;

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  /// Returns the closest point to the given point on the given line segment.
  @visibleForTesting
  static Vector3 getNearestPointOnLine(Vector3 point, Vector3 l1, Vector3 l2) {
    final double lengthSquared = math.pow(l2.x - l1.x, 2.0).toDouble()
        + math.pow(l2.y - l1.y, 2.0).toDouble();

    // In this case, l1 == l2.
    if (lengthSquared == 0) {
      return l1;
    }

    // Calculate how far down the line segment the closest point is and return
    // the point.
    final Vector3 l1P = point - l1;
    final Vector3 l1L2 = l2 - l1;
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    final double fraction = clampDouble(l1P.dot(l1L2) / lengthSquared, 0.0, 1.0);
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    return l1 + l1L2 * fraction;
  }

  /// Given a quad, return its axis aligned bounding box.
  @visibleForTesting
  static Quad getAxisAlignedBoundingBox(Quad quad) {
    final double minX = math.min(
      quad.point0.x,
      math.min(
        quad.point1.x,
        math.min(
          quad.point2.x,
          quad.point3.x,
        ),
      ),
    );
    final double minY = math.min(
      quad.point0.y,
      math.min(
        quad.point1.y,
        math.min(
          quad.point2.y,
          quad.point3.y,
        ),
      ),
    );
    final double maxX = math.max(
      quad.point0.x,
      math.max(
        quad.point1.x,
        math.max(
          quad.point2.x,
          quad.point3.x,
        ),
      ),
    );
    final double maxY = math.max(
      quad.point0.y,
      math.max(
        quad.point1.y,
        math.max(
          quad.point2.y,
          quad.point3.y,
        ),
      ),
    );
    return Quad.points(
      Vector3(minX, minY, 0),
      Vector3(maxX, minY, 0),
      Vector3(maxX, maxY, 0),
      Vector3(minX, maxY, 0),
    );
  }

  /// Returns true iff the point is inside the rectangle given by the Quad,
  /// inclusively.
  /// Algorithm from https://math.stackexchange.com/a/190373.
  @visibleForTesting
  static bool pointIsInside(Vector3 point, Quad quad) {
    final Vector3 aM = point - quad.point0;
    final Vector3 aB = quad.point1 - quad.point0;
    final Vector3 aD = quad.point3 - quad.point0;

    final double aMAB = aM.dot(aB);
    final double aBAB = aB.dot(aB);
    final double aMAD = aM.dot(aD);
    final double aDAD = aD.dot(aD);

    return 0 <= aMAB && aMAB <= aBAB && 0 <= aMAD && aMAD <= aDAD;
  }

  /// Get the point inside (inclusively) the given Quad that is nearest to the
  /// given Vector3.
  @visibleForTesting
  static Vector3 getNearestPointInside(Vector3 point, Quad quad) {
    // If the point is inside the axis aligned bounding box, then it's ok where
    // it is.
    if (pointIsInside(point, quad)) {
      return point;
    }

    // Otherwise, return the nearest point on the quad.
    final List<Vector3> closestPoints = <Vector3>[
      InteractiveViewer.getNearestPointOnLine(point, quad.point0, quad.point1),
      InteractiveViewer.getNearestPointOnLine(point, quad.point1, quad.point2),
      InteractiveViewer.getNearestPointOnLine(point, quad.point2, quad.point3),
      InteractiveViewer.getNearestPointOnLine(point, quad.point3, quad.point0),
    ];
    double minDistance = double.infinity;
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    late Vector3 closestOverall;
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    for (final Vector3 closePoint in closestPoints) {
      final double distance = math.sqrt(
        math.pow(point.x - closePoint.x, 2) + math.pow(point.y - closePoint.y, 2),
      );
      if (distance < minDistance) {
        minDistance = distance;
        closestOverall = closePoint;
      }
    }
    return closestOverall;
  }

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  @override
  State<InteractiveViewer> createState() => _InteractiveViewerState();
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}

class _InteractiveViewerState extends State<InteractiveViewer> with TickerProviderStateMixin {
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  TransformationController? _transformationController;
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  final GlobalKey _childKey = GlobalKey();
  final GlobalKey _parentKey = GlobalKey();
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  Animation<Offset>? _animation;
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  Animation<double>? _scaleAnimation;
  late Offset _scaleAnimationFocalPoint;
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  late AnimationController _controller;
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  late AnimationController _scaleController;
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  Axis? _currentAxis; // Used with panAxis.
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  Offset? _referenceFocalPoint; // Point where the current gesture began.
  double? _scaleStart; // Scale value at start of scaling gesture.
  double? _rotationStart = 0.0; // Rotation at start of rotation gesture.
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  double _currentRotation = 0.0; // Rotation of _transformationController.value.
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  _GestureType? _gestureType;
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  // TODO(justinmc): Add rotateEnabled parameter to the widget and remove this
  // hardcoded value when the rotation feature is implemented.
  // https://github.com/flutter/flutter/issues/57698
  final bool _rotateEnabled = false;

  // The _boundaryRect is calculated by adding the boundaryMargin to the size of
  // the child.
  Rect get _boundaryRect {
    assert(_childKey.currentContext != null);
    assert(!widget.boundaryMargin.left.isNaN);
    assert(!widget.boundaryMargin.right.isNaN);
    assert(!widget.boundaryMargin.top.isNaN);
    assert(!widget.boundaryMargin.bottom.isNaN);

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    final RenderBox childRenderBox = _childKey.currentContext!.findRenderObject()! as RenderBox;
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    final Size childSize = childRenderBox.size;
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    final Rect boundaryRect = widget.boundaryMargin.inflateRect(Offset.zero & childSize);
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    assert(
      !boundaryRect.isEmpty,
      "InteractiveViewer's child must have nonzero dimensions.",
    );
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    // Boundaries that are partially infinite are not allowed because Matrix4's
    // rotation and translation methods don't handle infinites well.
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    assert(
      boundaryRect.isFinite ||
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        (boundaryRect.left.isInfinite
        && boundaryRect.top.isInfinite
        && boundaryRect.right.isInfinite
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        && boundaryRect.bottom.isInfinite),
      'boundaryRect must either be infinite in all directions or finite in all directions.',
    );
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    return boundaryRect;
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  }

  // The Rect representing the child's parent.
  Rect get _viewport {
    assert(_parentKey.currentContext != null);
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    final RenderBox parentRenderBox = _parentKey.currentContext!.findRenderObject()! as RenderBox;
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    return Offset.zero & parentRenderBox.size;
  }

  // Return a new matrix representing the given matrix after applying the given
  // translation.
  Matrix4 _matrixTranslate(Matrix4 matrix, Offset translation) {
    if (translation == Offset.zero) {
      return matrix.clone();
    }

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    late final Offset alignedTranslation;

    if (_currentAxis != null) {
      switch(widget.panAxis){
        case PanAxis.horizontal:
          alignedTranslation = _alignAxis(translation, Axis.horizontal);
          break;
        case PanAxis.vertical:
          alignedTranslation = _alignAxis(translation, Axis.vertical);
          break;
        case PanAxis.aligned:
          alignedTranslation = _alignAxis(translation, _currentAxis!);
          break;
        case PanAxis.free:
          alignedTranslation = translation;
          break;
      }
    } else {
      alignedTranslation = translation;
    }
628

629
    final Matrix4 nextMatrix = matrix.clone()..translate(
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      alignedTranslation.dx,
      alignedTranslation.dy,
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    );

    // Transform the viewport to determine where its four corners will be after
    // the child has been transformed.
    final Quad nextViewport = _transformViewport(nextMatrix, _viewport);

    // If the boundaries are infinite, then no need to check if the translation
    // fits within them.
    if (_boundaryRect.isInfinite) {
      return nextMatrix;
    }

    // Expand the boundaries with rotation. This prevents the problem where a
    // mismatch in orientation between the viewport and boundaries effectively
    // limits translation. With this approach, all points that are visible with
    // no rotation are visible after rotation.
    final Quad boundariesAabbQuad = _getAxisAlignedBoundingBoxWithRotation(
      _boundaryRect,
      _currentRotation,
    );

    // If the given translation fits completely within the boundaries, allow it.
    final Offset offendingDistance = _exceedsBy(boundariesAabbQuad, nextViewport);
    if (offendingDistance == Offset.zero) {
      return nextMatrix;
    }

    // Desired translation goes out of bounds, so translate to the nearest
    // in-bounds point instead.
    final Offset nextTotalTranslation = _getMatrixTranslation(nextMatrix);
    final double currentScale = matrix.getMaxScaleOnAxis();
    final Offset correctedTotalTranslation = Offset(
      nextTotalTranslation.dx - offendingDistance.dx * currentScale,
      nextTotalTranslation.dy - offendingDistance.dy * currentScale,
    );
    // TODO(justinmc): This needs some work to handle rotation properly. The
    // idea is that the boundaries are axis aligned (boundariesAabbQuad), but
    // calculating the translation to put the viewport inside that Quad is more
    // complicated than this when rotated.
     // https://github.com/flutter/flutter/issues/57698
    final Matrix4 correctedMatrix = matrix.clone()..setTranslation(Vector3(
      correctedTotalTranslation.dx,
      correctedTotalTranslation.dy,
      0.0,
    ));

    // Double check that the corrected translation fits.
    final Quad correctedViewport = _transformViewport(correctedMatrix, _viewport);
    final Offset offendingCorrectedDistance = _exceedsBy(boundariesAabbQuad, correctedViewport);
    if (offendingCorrectedDistance == Offset.zero) {
      return correctedMatrix;
    }

    // If the corrected translation doesn't fit in either direction, don't allow
    // any translation at all. This happens when the viewport is larger than the
    // entire boundary.
    if (offendingCorrectedDistance.dx != 0.0 && offendingCorrectedDistance.dy != 0.0) {
      return matrix.clone();
    }

    // Otherwise, allow translation in only the direction that fits. This
    // happens when the viewport is larger than the boundary in one direction.
    final Offset unidirectionalCorrectedTotalTranslation = Offset(
      offendingCorrectedDistance.dx == 0.0 ? correctedTotalTranslation.dx : 0.0,
      offendingCorrectedDistance.dy == 0.0 ? correctedTotalTranslation.dy : 0.0,
    );
    return matrix.clone()..setTranslation(Vector3(
      unidirectionalCorrectedTotalTranslation.dx,
      unidirectionalCorrectedTotalTranslation.dy,
      0.0,
    ));
  }

  // Return a new matrix representing the given matrix after applying the given
  // scale.
  Matrix4 _matrixScale(Matrix4 matrix, double scale) {
    if (scale == 1.0) {
      return matrix.clone();
    }
    assert(scale != 0.0);

    // Don't allow a scale that results in an overall scale beyond min/max
    // scale.
715
    final double currentScale = _transformationController!.value.getMaxScaleOnAxis();
716 717 718 719 720 721 722 723 724
    final double totalScale = math.max(
      currentScale * scale,
      // Ensure that the scale cannot make the child so big that it can't fit
      // inside the boundaries (in either direction).
      math.max(
        _viewport.width / _boundaryRect.width,
        _viewport.height / _boundaryRect.height,
      ),
    );
725
    final double clampedTotalScale = clampDouble(totalScale,
726 727
      widget.minScale,
      widget.maxScale,
728
    );
729
    final double clampedScale = clampedTotalScale / currentScale;
730
    return matrix.clone()..scale(clampedScale);
731 732 733 734 735 736 737 738
  }

  // Return a new matrix representing the given matrix after applying the given
  // rotation.
  Matrix4 _matrixRotate(Matrix4 matrix, double rotation, Offset focalPoint) {
    if (rotation == 0) {
      return matrix.clone();
    }
739
    final Offset focalPointScene = _transformationController!.toScene(
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      focalPoint,
    );
    return matrix
      .clone()
      ..translate(focalPointScene.dx, focalPointScene.dy)
      ..rotateZ(-rotation)
      ..translate(-focalPointScene.dx, -focalPointScene.dy);
  }

  // Returns true iff the given _GestureType is enabled.
750
  bool _gestureIsSupported(_GestureType? gestureType) {
751 752 753 754 755 756 757 758
    switch (gestureType) {
      case _GestureType.rotate:
        return _rotateEnabled;

      case _GestureType.scale:
        return widget.scaleEnabled;

      case _GestureType.pan:
759
      case null:
760
        return widget.panEnabled;
761 762 763
    }
  }

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  // Decide which type of gesture this is by comparing the amount of scale
  // and rotation in the gesture, if any. Scale starts at 1 and rotation
  // starts at 0. Pan will have no scale and no rotation because it uses only one
  // finger.
  _GestureType _getGestureType(ScaleUpdateDetails details) {
    final double scale = !widget.scaleEnabled ? 1.0 : details.scale;
    final double rotation = !_rotateEnabled ? 0.0 : details.rotation;
    if ((scale - 1).abs() > rotation.abs()) {
      return _GestureType.scale;
    } else if (rotation != 0.0) {
      return _GestureType.rotate;
    } else {
      return _GestureType.pan;
    }
  }

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  // Handle the start of a gesture. All of pan, scale, and rotate are handled
  // with GestureDetector's scale gesture.
  void _onScaleStart(ScaleStartDetails details) {
783
    widget.onInteractionStart?.call(details);
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    if (_controller.isAnimating) {
      _controller.stop();
      _controller.reset();
      _animation?.removeListener(_onAnimate);
      _animation = null;
    }
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    if (_scaleController.isAnimating) {
      _scaleController.stop();
      _scaleController.reset();
      _scaleAnimation?.removeListener(_onScaleAnimate);
      _scaleAnimation = null;
    }
797 798

    _gestureType = null;
799
    _currentAxis = null;
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    _scaleStart = _transformationController!.value.getMaxScaleOnAxis();
    _referenceFocalPoint = _transformationController!.toScene(
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      details.localFocalPoint,
    );
    _rotationStart = _currentRotation;
  }

  // Handle an update to an ongoing gesture. All of pan, scale, and rotate are
  // handled with GestureDetector's scale gesture.
  void _onScaleUpdate(ScaleUpdateDetails details) {
810
    final double scale = _transformationController!.value.getMaxScaleOnAxis();
811
    _scaleAnimationFocalPoint = details.localFocalPoint;
812
    final Offset focalPointScene = _transformationController!.toScene(
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      details.localFocalPoint,
    );
815

816
    if (_gestureType == _GestureType.pan) {
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      // When a gesture first starts, it sometimes has no change in scale and
      // rotation despite being a two-finger gesture. Here the gesture is
      // allowed to be reinterpreted as its correct type after originally
      // being marked as a pan.
      _gestureType = _getGestureType(details);
    } else {
      _gestureType ??= _getGestureType(details);
824
    }
825
    if (!_gestureIsSupported(_gestureType)) {
826
      widget.onInteractionUpdate?.call(details);
827 828 829
      return;
    }

830
    switch (_gestureType!) {
831
      case _GestureType.scale:
832
        assert(_scaleStart != null);
833 834 835
        // details.scale gives us the amount to change the scale as of the
        // start of this gesture, so calculate the amount to scale as of the
        // previous call to _onScaleUpdate.
836
        final double desiredScale = _scaleStart! * details.scale;
837
        final double scaleChange = desiredScale / scale;
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        _transformationController!.value = _matrixScale(
          _transformationController!.value,
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          scaleChange,
        );

        // While scaling, translate such that the user's two fingers stay on
        // the same places in the scene. That means that the focal point of
        // the scale should be on the same place in the scene before and after
        // the scale.
847
        final Offset focalPointSceneScaled = _transformationController!.toScene(
848 849
          details.localFocalPoint,
        );
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        _transformationController!.value = _matrixTranslate(
          _transformationController!.value,
          focalPointSceneScaled - _referenceFocalPoint!,
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        );

        // details.localFocalPoint should now be at the same location as the
        // original _referenceFocalPoint point. If it's not, that's because
        // the translate came in contact with a boundary. In that case, update
        // _referenceFocalPoint so subsequent updates happen in relation to
        // the new effective focal point.
860
        final Offset focalPointSceneCheck = _transformationController!.toScene(
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          details.localFocalPoint,
        );
863
        if (_round(_referenceFocalPoint!) != _round(focalPointSceneCheck)) {
864 865
          _referenceFocalPoint = focalPointSceneCheck;
        }
866
        break;
867 868 869

      case _GestureType.rotate:
        if (details.rotation == 0.0) {
870
          widget.onInteractionUpdate?.call(details);
871 872
          return;
        }
873 874 875
        final double desiredRotation = _rotationStart! + details.rotation;
        _transformationController!.value = _matrixRotate(
          _transformationController!.value,
876 877 878 879
          _currentRotation - desiredRotation,
          details.localFocalPoint,
        );
        _currentRotation = desiredRotation;
880
        break;
881 882

      case _GestureType.pan:
883 884 885 886 887
        assert(_referenceFocalPoint != null);
        // details may have a change in scale here when scaleEnabled is false.
        // In an effort to keep the behavior similar whether or not scaleEnabled
        // is true, these gestures are thrown away.
        if (details.scale != 1.0) {
888
          widget.onInteractionUpdate?.call(details);
889 890
          return;
        }
891
        _currentAxis ??= _getPanAxis(_referenceFocalPoint!, focalPointScene);
892 893
        // Translate so that the same point in the scene is underneath the
        // focal point before and after the movement.
894 895 896
        final Offset translationChange = focalPointScene - _referenceFocalPoint!;
        _transformationController!.value = _matrixTranslate(
          _transformationController!.value,
897 898
          translationChange,
        );
899
        _referenceFocalPoint = _transformationController!.toScene(
900 901
          details.localFocalPoint,
        );
902
        break;
903
    }
904
    widget.onInteractionUpdate?.call(details);
905 906 907 908 909
  }

  // Handle the end of a gesture of _GestureType. All of pan, scale, and rotate
  // are handled with GestureDetector's scale gesture.
  void _onScaleEnd(ScaleEndDetails details) {
910
    widget.onInteractionEnd?.call(details);
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    _scaleStart = null;
    _rotationStart = null;
    _referenceFocalPoint = null;

    _animation?.removeListener(_onAnimate);
916
    _scaleAnimation?.removeListener(_onScaleAnimate);
917
    _controller.reset();
918
    _scaleController.reset();
919 920

    if (!_gestureIsSupported(_gestureType)) {
921
      _currentAxis = null;
922 923 924
      return;
    }

925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977
    if (_gestureType == _GestureType.pan) {
      if (details.velocity.pixelsPerSecond.distance < kMinFlingVelocity) {
        _currentAxis = null;
        return;
      }
      final Vector3 translationVector = _transformationController!.value.getTranslation();
      final Offset translation = Offset(translationVector.x, translationVector.y);
      final FrictionSimulation frictionSimulationX = FrictionSimulation(
        widget.interactionEndFrictionCoefficient,
        translation.dx,
        details.velocity.pixelsPerSecond.dx,
      );
      final FrictionSimulation frictionSimulationY = FrictionSimulation(
        widget.interactionEndFrictionCoefficient,
        translation.dy,
        details.velocity.pixelsPerSecond.dy,
      );
      final double tFinal = _getFinalTime(
        details.velocity.pixelsPerSecond.distance,
        widget.interactionEndFrictionCoefficient,
      );
      _animation = Tween<Offset>(
        begin: translation,
        end: Offset(frictionSimulationX.finalX, frictionSimulationY.finalX),
      ).animate(CurvedAnimation(
        parent: _controller,
        curve: Curves.decelerate,
      ));
      _controller.duration = Duration(milliseconds: (tFinal * 1000).round());
      _animation!.addListener(_onAnimate);
      _controller.forward();
    } else if (_gestureType == _GestureType.scale) {
      if (details.scaleVelocity.abs() < 0.1) {
        _currentAxis = null;
        return;
      }
      final double scale = _transformationController!.value.getMaxScaleOnAxis();
      final FrictionSimulation frictionSimulation = FrictionSimulation(
        widget.interactionEndFrictionCoefficient * widget.scaleFactor,
        scale,
        details.scaleVelocity / 10
      );
      final double tFinal = _getFinalTime(details.scaleVelocity.abs(), widget.interactionEndFrictionCoefficient, effectivelyMotionless: 0.1);
      _scaleAnimation = Tween<double>(
        begin: scale,
        end: frictionSimulation.x(tFinal)
      ).animate(CurvedAnimation(
        parent: _scaleController,
        curve: Curves.decelerate
      ));
      _scaleController.duration = Duration(milliseconds: (tFinal * 1000).round());
      _scaleAnimation!.addListener(_onScaleAnimate);
      _scaleController.forward();
978 979 980
    }
  }

981
  // Handle mousewheel and web trackpad scroll events.
982
  void _receivedPointerSignal(PointerSignalEvent event) {
983
    final double scaleChange;
984
    if (event is PointerScrollEvent) {
985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031
      if (event.kind == PointerDeviceKind.trackpad) {
        // Trackpad scroll, so treat it as a pan.
        widget.onInteractionStart?.call(
          ScaleStartDetails(
            focalPoint: event.position,
            localFocalPoint: event.localPosition,
          ),
        );

        final Offset localDelta = PointerEvent.transformDeltaViaPositions(
          untransformedEndPosition: event.position + event.scrollDelta,
          untransformedDelta: event.scrollDelta,
          transform: event.transform,
        );

        if (!_gestureIsSupported(_GestureType.pan)) {
          widget.onInteractionUpdate?.call(ScaleUpdateDetails(
            focalPoint: event.position - event.scrollDelta,
            localFocalPoint: event.localPosition - event.scrollDelta,
            focalPointDelta: -localDelta,
          ));
          widget.onInteractionEnd?.call(ScaleEndDetails());
          return;
        }

        final Offset focalPointScene = _transformationController!.toScene(
          event.localPosition,
        );

        final Offset newFocalPointScene = _transformationController!.toScene(
          event.localPosition - localDelta,
        );

        _transformationController!.value = _matrixTranslate(
          _transformationController!.value,
          newFocalPointScene - focalPointScene
        );

        widget.onInteractionUpdate?.call(ScaleUpdateDetails(
          focalPoint: event.position - event.scrollDelta,
          localFocalPoint: event.localPosition - localDelta,
          focalPointDelta: -localDelta
        ));
        widget.onInteractionEnd?.call(ScaleEndDetails());
        return;
      }
      // Ignore left and right mouse wheel scroll.
1032 1033 1034
      if (event.scrollDelta.dy == 0.0) {
        return;
      }
1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048
      scaleChange = math.exp(-event.scrollDelta.dy / widget.scaleFactor);
    }
    else if (event is PointerScaleEvent) {
      scaleChange = event.scale;
    }
    else {
      return;
    }
    widget.onInteractionStart?.call(
      ScaleStartDetails(
        focalPoint: event.position,
        localFocalPoint: event.localPosition,
      ),
    );
1049

1050
    if (!_gestureIsSupported(_GestureType.scale)) {
1051 1052 1053 1054 1055 1056
      widget.onInteractionUpdate?.call(ScaleUpdateDetails(
        focalPoint: event.position,
        localFocalPoint: event.localPosition,
        scale: scaleChange,
      ));
      widget.onInteractionEnd?.call(ScaleEndDetails());
1057
      return;
1058
    }
1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084

    final Offset focalPointScene = _transformationController!.toScene(
      event.localPosition,
    );

    _transformationController!.value = _matrixScale(
      _transformationController!.value,
      scaleChange,
    );

    // After scaling, translate such that the event's position is at the
    // same scene point before and after the scale.
    final Offset focalPointSceneScaled = _transformationController!.toScene(
      event.localPosition,
    );
    _transformationController!.value = _matrixTranslate(
      _transformationController!.value,
      focalPointSceneScaled - focalPointScene,
    );

    widget.onInteractionUpdate?.call(ScaleUpdateDetails(
      focalPoint: event.position,
      localFocalPoint: event.localPosition,
      scale: scaleChange,
    ));
    widget.onInteractionEnd?.call(ScaleEndDetails());
1085 1086 1087 1088 1089
  }

  // Handle inertia drag animation.
  void _onAnimate() {
    if (!_controller.isAnimating) {
1090
      _currentAxis = null;
1091 1092 1093 1094 1095 1096
      _animation?.removeListener(_onAnimate);
      _animation = null;
      _controller.reset();
      return;
    }
    // Translate such that the resulting translation is _animation.value.
1097
    final Vector3 translationVector = _transformationController!.value.getTranslation();
1098
    final Offset translation = Offset(translationVector.x, translationVector.y);
1099
    final Offset translationScene = _transformationController!.toScene(
1100 1101
      translation,
    );
1102 1103
    final Offset animationScene = _transformationController!.toScene(
      _animation!.value,
1104 1105
    );
    final Offset translationChangeScene = animationScene - translationScene;
1106 1107
    _transformationController!.value = _matrixTranslate(
      _transformationController!.value,
1108 1109 1110 1111
      translationChangeScene,
    );
  }

1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143
  // Handle inertia scale animation.
  void _onScaleAnimate() {
    if (!_scaleController.isAnimating) {
      _currentAxis = null;
      _scaleAnimation?.removeListener(_onScaleAnimate);
      _scaleAnimation = null;
      _scaleController.reset();
      return;
    }
    final double desiredScale = _scaleAnimation!.value;
    final double scaleChange = desiredScale / _transformationController!.value.getMaxScaleOnAxis();
    final Offset referenceFocalPoint = _transformationController!.toScene(
      _scaleAnimationFocalPoint,
    );
    _transformationController!.value = _matrixScale(
      _transformationController!.value,
      scaleChange,
    );

    // While scaling, translate such that the user's two fingers stay on
    // the same places in the scene. That means that the focal point of
    // the scale should be on the same place in the scene before and after
    // the scale.
    final Offset focalPointSceneScaled = _transformationController!.toScene(
      _scaleAnimationFocalPoint,
    );
    _transformationController!.value = _matrixTranslate(
      _transformationController!.value,
      focalPointSceneScaled - referenceFocalPoint,
    );
  }

1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155
  void _onTransformationControllerChange() {
    // A change to the TransformationController's value is a change to the
    // state.
    setState(() {});
  }

  @override
  void initState() {
    super.initState();

    _transformationController = widget.transformationController
        ?? TransformationController();
1156
    _transformationController!.addListener(_onTransformationControllerChange);
1157 1158 1159
    _controller = AnimationController(
      vsync: this,
    );
1160 1161 1162
    _scaleController = AnimationController(
      vsync: this
    );
1163 1164 1165 1166 1167 1168 1169 1170 1171
  }

  @override
  void didUpdateWidget(InteractiveViewer oldWidget) {
    super.didUpdateWidget(oldWidget);
    // Handle all cases of needing to dispose and initialize
    // transformationControllers.
    if (oldWidget.transformationController == null) {
      if (widget.transformationController != null) {
1172 1173
        _transformationController!.removeListener(_onTransformationControllerChange);
        _transformationController!.dispose();
1174
        _transformationController = widget.transformationController;
1175
        _transformationController!.addListener(_onTransformationControllerChange);
1176 1177 1178
      }
    } else {
      if (widget.transformationController == null) {
1179
        _transformationController!.removeListener(_onTransformationControllerChange);
1180
        _transformationController = TransformationController();
1181
        _transformationController!.addListener(_onTransformationControllerChange);
1182
      } else if (widget.transformationController != oldWidget.transformationController) {
1183
        _transformationController!.removeListener(_onTransformationControllerChange);
1184
        _transformationController = widget.transformationController;
1185
        _transformationController!.addListener(_onTransformationControllerChange);
1186 1187 1188 1189 1190 1191 1192
      }
    }
  }

  @override
  void dispose() {
    _controller.dispose();
1193
    _scaleController.dispose();
1194
    _transformationController!.removeListener(_onTransformationControllerChange);
1195
    if (widget.transformationController == null) {
1196
      _transformationController!.dispose();
1197 1198 1199 1200
    }
    super.dispose();
  }

1201 1202 1203 1204 1205 1206 1207 1208 1209
  @override
  Widget build(BuildContext context) {
    Widget child;
    if (widget.child != null) {
      child = _InteractiveViewerBuilt(
        childKey: _childKey,
        clipBehavior: widget.clipBehavior,
        constrained: widget.constrained,
        matrix: _transformationController!.value,
1210
        alignment: widget.alignment,
1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224
        child: widget.child!,
      );
    } else {
      // When using InteractiveViewer.builder, then constrained is false and the
      // viewport is the size of the constraints.
      assert(widget.builder != null);
      assert(!widget.constrained);
      child = LayoutBuilder(
        builder: (BuildContext context, BoxConstraints constraints) {
          final Matrix4 matrix = _transformationController!.value;
          return _InteractiveViewerBuilt(
            childKey: _childKey,
            clipBehavior: widget.clipBehavior,
            constrained: widget.constrained,
1225
            alignment: widget.alignment,
1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243
            matrix: matrix,
            child: widget.builder!(
              context,
              _transformViewport(matrix, Offset.zero & constraints.biggest),
            ),
          );
        },
      );
    }

    return Listener(
      key: _parentKey,
      onPointerSignal: _receivedPointerSignal,
      child: GestureDetector(
        behavior: HitTestBehavior.opaque, // Necessary when panning off screen.
        onScaleEnd: _onScaleEnd,
        onScaleStart: _onScaleStart,
        onScaleUpdate: _onScaleUpdate,
1244 1245
        trackpadScrollCausesScale: widget.trackpadScrollCausesScale,
        trackpadScrollToScaleFactor: Offset(0, -1/widget.scaleFactor),
1246 1247 1248 1249 1250 1251
        child: child,
      ),
    );
  }
}

1252
// This widget allows us to easily swap in and out the LayoutBuilder in
1253 1254 1255 1256 1257 1258 1259 1260
// InteractiveViewer's depending on if it's using a builder or a child.
class _InteractiveViewerBuilt extends StatelessWidget {
  const _InteractiveViewerBuilt({
    required this.child,
    required this.childKey,
    required this.clipBehavior,
    required this.constrained,
    required this.matrix,
1261
    required this.alignment,
1262
  });
1263 1264 1265 1266 1267 1268

  final Widget child;
  final GlobalKey childKey;
  final Clip clipBehavior;
  final bool constrained;
  final Matrix4 matrix;
1269
  final Alignment? alignment;
1270

1271 1272
  @override
  Widget build(BuildContext context) {
1273
    Widget child = Transform(
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      transform: matrix,
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      alignment: alignment,
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      child: KeyedSubtree(
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        key: childKey,
        child: this.child,
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      ),
    );

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    if (!constrained) {
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      child = OverflowBox(
        alignment: Alignment.topLeft,
        minWidth: 0.0,
        minHeight: 0.0,
        maxWidth: double.infinity,
        maxHeight: double.infinity,
        child: child,
      );
    }

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    return ClipRect(
      clipBehavior: clipBehavior,
      child: child,
    );
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  }
}

/// A thin wrapper on [ValueNotifier] whose value is a [Matrix4] representing a
/// transformation.
///
/// The [value] defaults to the identity matrix, which corresponds to no
/// transformation.
///
/// See also:
///
///  * [InteractiveViewer.transformationController] for detailed documentation
///    on how to use TransformationController with [InteractiveViewer].
class TransformationController extends ValueNotifier<Matrix4> {
  /// Create an instance of [TransformationController].
  ///
  /// The [value] defaults to the identity matrix, which corresponds to no
  /// transformation.
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  TransformationController([Matrix4? value]) : super(value ?? Matrix4.identity());
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  /// Return the scene point at the given viewport point.
  ///
  /// A viewport point is relative to the parent while a scene point is relative
  /// to the child, regardless of transformation. Calling toScene with a
  /// viewport point essentially returns the scene coordinate that lies
  /// underneath the viewport point given the transform.
  ///
  /// The viewport transforms as the inverse of the child (i.e. moving the child
  /// left is equivalent to moving the viewport right).
  ///
  /// This method is often useful when determining where an event on the parent
  /// occurs on the child. This example shows how to determine where a tap on
  /// the parent occurred on the child.
  ///
  /// ```dart
  /// @override
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  /// Widget build(BuildContext context) {
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  ///   return GestureDetector(
  ///     onTapUp: (TapUpDetails details) {
  ///       _childWasTappedAt = _transformationController.toScene(
  ///         details.localPosition,
  ///       );
  ///     },
  ///     child: InteractiveViewer(
  ///       transformationController: _transformationController,
  ///       child: child,
  ///     ),
  ///   );
  /// }
  /// ```
  Offset toScene(Offset viewportPoint) {
    // On viewportPoint, perform the inverse transformation of the scene to get
    // where the point would be in the scene before the transformation.
    final Matrix4 inverseMatrix = Matrix4.inverted(value);
    final Vector3 untransformed = inverseMatrix.transform3(Vector3(
      viewportPoint.dx,
      viewportPoint.dy,
      0,
    ));
    return Offset(untransformed.x, untransformed.y);
  }
}

// A classification of relevant user gestures. Each contiguous user gesture is
// represented by exactly one _GestureType.
enum _GestureType {
  pan,
  scale,
  rotate,
}

// Given a velocity and drag, calculate the time at which motion will come to
// a stop, within the margin of effectivelyMotionless.
1370
double _getFinalTime(double velocity, double drag, {double effectivelyMotionless = 10}) {
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  return math.log(effectivelyMotionless / velocity) / math.log(drag / 100);
}

// Return the translation from the given Matrix4 as an Offset.
Offset _getMatrixTranslation(Matrix4 matrix) {
  final Vector3 nextTranslation = matrix.getTranslation();
  return Offset(nextTranslation.x, nextTranslation.y);
}

// Transform the four corners of the viewport by the inverse of the given
// matrix. This gives the viewport after the child has been transformed by the
// given matrix. The viewport transforms as the inverse of the child (i.e.
// moving the child left is equivalent to moving the viewport right).
Quad _transformViewport(Matrix4 matrix, Rect viewport) {
  final Matrix4 inverseMatrix = matrix.clone()..invert();
  return Quad.points(
    inverseMatrix.transform3(Vector3(
      viewport.topLeft.dx,
      viewport.topLeft.dy,
      0.0,
    )),
    inverseMatrix.transform3(Vector3(
      viewport.topRight.dx,
      viewport.topRight.dy,
      0.0,
    )),
    inverseMatrix.transform3(Vector3(
      viewport.bottomRight.dx,
      viewport.bottomRight.dy,
      0.0,
    )),
    inverseMatrix.transform3(Vector3(
      viewport.bottomLeft.dx,
      viewport.bottomLeft.dy,
      0.0,
    )),
  );
}

// Find the axis aligned bounding box for the rect rotated about its center by
// the given amount.
Quad _getAxisAlignedBoundingBoxWithRotation(Rect rect, double rotation) {
  final Matrix4 rotationMatrix = Matrix4.identity()
      ..translate(rect.size.width / 2, rect.size.height / 2)
      ..rotateZ(rotation)
      ..translate(-rect.size.width / 2, -rect.size.height / 2);
  final Quad boundariesRotated = Quad.points(
    rotationMatrix.transform3(Vector3(rect.left, rect.top, 0.0)),
    rotationMatrix.transform3(Vector3(rect.right, rect.top, 0.0)),
    rotationMatrix.transform3(Vector3(rect.right, rect.bottom, 0.0)),
    rotationMatrix.transform3(Vector3(rect.left, rect.bottom, 0.0)),
  );
  return InteractiveViewer.getAxisAlignedBoundingBox(boundariesRotated);
}

// Return the amount that viewport lies outside of boundary. If the viewport
// is completely contained within the boundary (inclusively), then returns
// Offset.zero.
Offset _exceedsBy(Quad boundary, Quad viewport) {
  final List<Vector3> viewportPoints = <Vector3>[
    viewport.point0, viewport.point1, viewport.point2, viewport.point3,
  ];
  Offset largestExcess = Offset.zero;
  for (final Vector3 point in viewportPoints) {
    final Vector3 pointInside = InteractiveViewer.getNearestPointInside(point, boundary);
    final Offset excess = Offset(
      pointInside.x - point.x,
      pointInside.y - point.y,
    );
    if (excess.dx.abs() > largestExcess.dx.abs()) {
      largestExcess = Offset(excess.dx, largestExcess.dy);
    }
    if (excess.dy.abs() > largestExcess.dy.abs()) {
      largestExcess = Offset(largestExcess.dx, excess.dy);
    }
  }

  return _round(largestExcess);
}

// Round the output values. This works around a precision problem where
// values that should have been zero were given as within 10^-10 of zero.
Offset _round(Offset offset) {
  return Offset(
    double.parse(offset.dx.toStringAsFixed(9)),
    double.parse(offset.dy.toStringAsFixed(9)),
  );
}
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// Align the given offset to the given axis by allowing movement only in the
// axis direction.
Offset _alignAxis(Offset offset, Axis axis) {
  switch (axis) {
    case Axis.horizontal:
      return Offset(offset.dx, 0.0);
    case Axis.vertical:
      return Offset(0.0, offset.dy);
  }
}

// Given two points, return the axis where the distance between the points is
// greatest. If they are equal, return null.
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Axis? _getPanAxis(Offset point1, Offset point2) {
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  if (point1 == point2) {
    return null;
  }
  final double x = point2.dx - point1.dx;
  final double y = point2.dy - point1.dy;
  return x.abs() > y.abs() ? Axis.horizontal : Axis.vertical;
}
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/// This enum is used to specify the behavior of the [InteractiveViewer] when
/// the user drags the viewport.
enum PanAxis{
  /// The user can only pan the viewport along the horizontal axis.
  horizontal,

  /// The user can only pan the viewport along the vertical axis.
  vertical,

  /// The user can pan the viewport along the horizontal and vertical axes
  /// but not diagonally.
  aligned,

  /// The user can pan the viewport freely in any direction.
  free,
}