animated_size.dart 10.9 KB
Newer Older
Ian Hickson's avatar
Ian Hickson committed
1
// Copyright 2014 The Flutter Authors. All rights reserved.
2 3 4 5
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/animation.dart';
6
import 'package:flutter/foundation.dart';
7
import 'package:flutter/scheduler.dart';
8 9

import 'box.dart';
10
import 'layer.dart';
11 12 13
import 'object.dart';
import 'shifted_box.dart';

14 15 16 17 18 19
/// A [RenderAnimatedSize] can be in exactly one of these states.
@visibleForTesting
enum RenderAnimatedSizeState {
  /// The initial state, when we do not yet know what the starting and target
  /// sizes are to animate.
  ///
20
  /// The next state is [stable].
21 22 23 24 25
  start,

  /// At this state the child's size is assumed to be stable and we are either
  /// animating, or waiting for the child's size to change.
  ///
26 27
  /// If the child's size changes, the state will become [changed]. Otherwise,
  /// it remains [stable].
28 29 30 31 32
  stable,

  /// At this state we know that the child has changed once after being assumed
  /// [stable].
  ///
33
  /// The next state will be one of:
34
  ///
35 36 37 38 39
  /// * [stable] if the child's size stabilized immediately. This is a signal
  ///   for the render object to begin animating the size towards the child's new
  ///   size.
  ///
  /// * [unstable] if the child's size continues to change.
40 41
  changed,

42 43
  /// At this state the child's size is assumed to be unstable (changing each
  /// frame).
44
  ///
45 46
  /// Instead of chasing the child's size in this state, the render object
  /// tightly tracks the child's size until it stabilizes.
47
  ///
48 49 50
  /// The render object remains in this state until a frame where the child's
  /// size remains the same as the previous frame. At that time, the next state
  /// is [stable].
51 52 53
  unstable,
}

54
/// A render object that animates its size to its child's size over a given
55 56 57 58 59
/// [duration] and with a given [curve]. If the child's size itself animates
/// (i.e. if it changes size two frames in a row, as opposed to abruptly
/// changing size in one frame then remaining that size in subsequent frames),
/// this render object sizes itself to fit the child instead of animating
/// itself.
60
///
61 62
/// When the child overflows the current animated size of this render object, it
/// is clipped.
63 64
class RenderAnimatedSize extends RenderAligningShiftedBox {
  /// Creates a render object that animates its size to match its child.
65 66 67
  /// The [duration] and [curve] arguments define the animation.
  ///
  /// The [alignment] argument is used to align the child when the parent is not
68 69
  /// (yet) the same size as the child.
  ///
70 71 72 73 74 75 76
  /// The [duration] is required.
  ///
  /// The [vsync] should specify a [TickerProvider] for the animation
  /// controller.
  ///
  /// The arguments [duration], [curve], [alignment], and [vsync] must
  /// not be null.
77
  RenderAnimatedSize({
78 79 80
    required TickerProvider vsync,
    required Duration duration,
    Duration? reverseDuration,
81 82
    Curve curve = Curves.linear,
    AlignmentGeometry alignment = Alignment.center,
83 84
    TextDirection? textDirection,
    RenderBox? child,
85
    Clip clipBehavior = Clip.hardEdge,
86 87 88
  }) : assert(vsync != null),
       assert(duration != null),
       assert(curve != null),
89
       assert(clipBehavior != null),
90
       _vsync = vsync,
91
       _clipBehavior = clipBehavior,
92
       super(child: child, alignment: alignment, textDirection: textDirection) {
93
    _controller = AnimationController(
94 95
      vsync: vsync,
      duration: duration,
96
      reverseDuration: reverseDuration,
97 98 99 100
    )..addListener(() {
      if (_controller.value != _lastValue)
        markNeedsLayout();
    });
101
    _animation = CurvedAnimation(
102
      parent: _controller,
103
      curve: curve,
104 105 106
    );
  }

107 108
  late final AnimationController _controller;
  late final CurvedAnimation _animation;
109
  final SizeTween _sizeTween = SizeTween();
110 111
  late bool _hasVisualOverflow;
  double? _lastValue;
112

113 114 115 116 117 118 119
  /// The state this size animation is in.
  ///
  /// See [RenderAnimatedSizeState] for possible states.
  @visibleForTesting
  RenderAnimatedSizeState get state => _state;
  RenderAnimatedSizeState _state = RenderAnimatedSizeState.start;

120
  /// The duration of the animation.
121
  Duration get duration => _controller.duration!;
122 123 124 125 126 127 128
  set duration(Duration value) {
    assert(value != null);
    if (value == _controller.duration)
      return;
    _controller.duration = value;
  }

129
  /// The duration of the animation when running in reverse.
130 131
  Duration? get reverseDuration => _controller.reverseDuration;
  set reverseDuration(Duration? value) {
132 133 134 135 136
    if (value == _controller.reverseDuration)
      return;
    _controller.reverseDuration = value;
  }

137 138 139 140 141 142 143 144 145
  /// The curve of the animation.
  Curve get curve => _animation.curve;
  set curve(Curve value) {
    assert(value != null);
    if (value == _animation.curve)
      return;
    _animation.curve = value;
  }

146
  /// {@macro flutter.material.Material.clipBehavior}
147 148 149 150 151 152 153 154 155 156 157 158 159
  ///
  /// Defaults to [Clip.hardEdge], and must not be null.
  Clip get clipBehavior => _clipBehavior;
  Clip _clipBehavior = Clip.hardEdge;
  set clipBehavior(Clip value) {
    assert(value != null);
    if (value != _clipBehavior) {
      _clipBehavior = value;
      markNeedsPaint();
      markNeedsSemanticsUpdate();
    }
  }

160 161 162 163 164 165
  /// Whether the size is being currently animated towards the child's size.
  ///
  /// See [RenderAnimatedSizeState] for situations when we may not be animating
  /// the size.
  bool get isAnimating => _controller.isAnimating;

166 167 168 169 170 171 172 173 174 175 176
  /// The [TickerProvider] for the [AnimationController] that runs the animation.
  TickerProvider get vsync => _vsync;
  TickerProvider _vsync;
  set vsync(TickerProvider value) {
    assert(value != null);
    if (value == _vsync)
      return;
    _vsync = value;
    _controller.resync(vsync);
  }

177 178 179 180 181 182
  @override
  void detach() {
    _controller.stop();
    super.detach();
  }

183
  Size? get _animatedSize {
184 185 186 187 188 189 190
    return _sizeTween.evaluate(_animation);
  }

  @override
  void performLayout() {
    _lastValue = _controller.value;
    _hasVisualOverflow = false;
191
    final BoxConstraints constraints = this.constraints;
192 193
    if (child == null || constraints.isTight) {
      _controller.stop();
194
      size = _sizeTween.begin = _sizeTween.end = constraints.smallest;
195 196
      _state = RenderAnimatedSizeState.start;
      child?.layout(constraints);
197 198 199
      return;
    }

200
    child!.layout(constraints, parentUsesSize: true);
201

202 203
    assert(_state != null);
    switch (_state) {
204 205 206 207 208 209 210 211 212 213 214 215
      case RenderAnimatedSizeState.start:
        _layoutStart();
        break;
      case RenderAnimatedSizeState.stable:
        _layoutStable();
        break;
      case RenderAnimatedSizeState.changed:
        _layoutChanged();
        break;
      case RenderAnimatedSizeState.unstable:
        _layoutUnstable();
        break;
216 217
    }

218
    size = constraints.constrain(_animatedSize!);
219 220
    alignChild();

221 222
    if (size.width < _sizeTween.end!.width ||
        size.height < _sizeTween.end!.height)
223 224 225
      _hasVisualOverflow = true;
  }

226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257
  @override
  Size computeDryLayout(BoxConstraints constraints) {
    if (child == null || constraints.isTight) {
      return constraints.smallest;
    }

    // This simplified version of performLayout only calculates the current
    // size without modifying global state. See performLayout for comments
    // explaining the rational behind the implementation.
    final Size childSize = child!.getDryLayout(constraints);
    assert(_state != null);
    switch (_state) {
      case RenderAnimatedSizeState.start:
        return constraints.constrain(childSize);
      case RenderAnimatedSizeState.stable:
        if (_sizeTween.end != childSize) {
          return constraints.constrain(size);
        } else if (_controller.value == _controller.upperBound) {
          return constraints.constrain(childSize);
        }
        break;
      case RenderAnimatedSizeState.unstable:
      case RenderAnimatedSizeState.changed:
        if (_sizeTween.end != childSize) {
          return constraints.constrain(childSize);
        }
        break;
    }

    return constraints.constrain(_animatedSize!);
  }

258 259 260 261 262 263 264 265 266 267
  void _restartAnimation() {
    _lastValue = 0.0;
    _controller.forward(from: 0.0);
  }

  /// Laying out the child for the first time.
  ///
  /// We have the initial size to animate from, but we do not have the target
  /// size to animate to, so we set both ends to child's size.
  void _layoutStart() {
268
    _sizeTween.begin = _sizeTween.end = debugAdoptSize(child!.size);
269 270 271 272 273 274 275 276 277
    _state = RenderAnimatedSizeState.stable;
  }

  /// At this state we're assuming the child size is stable and letting the
  /// animation run its course.
  ///
  /// If during animation the size of the child changes we restart the
  /// animation.
  void _layoutStable() {
278
    if (_sizeTween.end != child!.size) {
279
      _sizeTween.begin = size;
280
      _sizeTween.end = debugAdoptSize(child!.size);
281 282 283 284
      _restartAnimation();
      _state = RenderAnimatedSizeState.changed;
    } else if (_controller.value == _controller.upperBound) {
      // Animation finished. Reset target sizes.
285
      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child!.size);
286 287
    } else if (!_controller.isAnimating) {
      _controller.forward(); // resume the animation after being detached
288 289 290 291 292 293 294 295 296 297
    }
  }

  /// This state indicates that the size of the child changed once after being
  /// considered stable.
  ///
  /// If the child stabilizes immediately, we go back to stable state. If it
  /// changes again, we match the child's size, restart animation and go to
  /// unstable state.
  void _layoutChanged() {
298
    if (_sizeTween.end != child!.size) {
299
      // Child size changed again. Match the child's size and restart animation.
300
      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child!.size);
301 302 303 304 305
      _restartAnimation();
      _state = RenderAnimatedSizeState.unstable;
    } else {
      // Child size stabilized.
      _state = RenderAnimatedSizeState.stable;
306 307
      if (!_controller.isAnimating)
        _controller.forward(); // resume the animation after being detached
308 309 310 311 312 313 314
    }
  }

  /// The child's size is not stable.
  ///
  /// Continue tracking the child's size until is stabilizes.
  void _layoutUnstable() {
315
    if (_sizeTween.end != child!.size) {
316
      // Still unstable. Continue tracking the child.
317
      _sizeTween.begin = _sizeTween.end = debugAdoptSize(child!.size);
318 319 320 321 322 323 324 325
      _restartAnimation();
    } else {
      // Child size stabilized.
      _controller.stop();
      _state = RenderAnimatedSizeState.stable;
    }
  }

326 327
  @override
  void paint(PaintingContext context, Offset offset) {
328
    if (child != null && _hasVisualOverflow && clipBehavior != Clip.none) {
329
      final Rect rect = Offset.zero & size;
330
      _clipRectLayer.layer = context.pushClipRect(
331 332 333 334 335
        needsCompositing,
        offset,
        rect,
        super.paint,
        clipBehavior: clipBehavior,
336
        oldLayer: _clipRectLayer.layer,
337
      );
338
    } else {
339
      _clipRectLayer.layer = null;
340 341 342
      super.paint(context, offset);
    }
  }
343

344 345 346 347 348 349 350
  final LayerHandle<ClipRectLayer> _clipRectLayer = LayerHandle<ClipRectLayer>();

  @override
  void dispose() {
    _clipRectLayer.layer = null;
    super.dispose();
  }
351
}