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[framework] allow disabling image filter layer (#102085)
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@ -11,6 +11,19 @@ import 'framework.dart';
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/// Applies an [ImageFilter] to its child.
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///
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/// An image filter will always apply its filter operation to the child widget,
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/// even if said filter is conceptually a "no-op", such as an ImageFilter.blur
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/// with a radius of 0 or an ImageFilter.matrix with an identity matrix. Setting
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/// [ImageFiltered.enabled] to `false` is a more efficient manner of disabling
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/// an image filter.
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///
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/// The framework does not attempt to optimize out "no-op" filters because it
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/// cannot tell the difference between an intentional no-op and a filter that is
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/// only incidentally a no-op. Consider an ImageFilter.matrix that is animated
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/// and happens to pass through the identity matrix. If the framework identified it
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/// as a no-op it would drop and then recreate the layer during the animation which
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/// would be more expensive than keeping it around.
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///
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/// {@youtube 560 315 https://www.youtube.com/watch?v=7Lftorq4i2o}
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///
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/// See also:
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@ -27,17 +40,27 @@ class ImageFiltered extends SingleChildRenderObjectWidget {
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super.key,
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required this.imageFilter,
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super.child,
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this.enabled = true,
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}) : assert(imageFilter != null);
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/// The image filter to apply to the child of this widget.
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final ImageFilter imageFilter;
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/// Whether or not to apply the image filter opation to the child of this
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/// widget.
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///
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/// Prefer setting enabled to `false` instead of creating a "no-op" filter
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/// type for performance reasons.
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final bool enabled;
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@override
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RenderObject createRenderObject(BuildContext context) => _ImageFilterRenderObject(imageFilter);
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RenderObject createRenderObject(BuildContext context) => _ImageFilterRenderObject(imageFilter, enabled);
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@override
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void updateRenderObject(BuildContext context, RenderObject renderObject) {
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(renderObject as _ImageFilterRenderObject).imageFilter = imageFilter;
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(renderObject as _ImageFilterRenderObject)
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..enabled = enabled
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..imageFilter = imageFilter;
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}
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@override
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@ -48,7 +71,17 @@ class ImageFiltered extends SingleChildRenderObjectWidget {
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}
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class _ImageFilterRenderObject extends RenderProxyBox {
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_ImageFilterRenderObject(this._imageFilter);
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_ImageFilterRenderObject(this._imageFilter, this._enabled);
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bool get enabled => _enabled;
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bool _enabled;
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set enabled(bool value) {
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if (enabled == value) {
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return;
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}
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_enabled = value;
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markNeedsPaint();
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}
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ImageFilter get imageFilter => _imageFilter;
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ImageFilter _imageFilter;
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@ -61,11 +94,16 @@ class _ImageFilterRenderObject extends RenderProxyBox {
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}
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@override
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bool get alwaysNeedsCompositing => child != null;
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bool get alwaysNeedsCompositing => child != null && enabled;
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@override
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void paint(PaintingContext context, Offset offset) {
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assert(imageFilter != null);
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if (!enabled) {
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layer = null;
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return super.paint(context, offset);
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}
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if (layer == null) {
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layer = ImageFilterLayer(imageFilter: imageFilter);
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} else {
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@ -86,4 +86,25 @@ void main() {
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await pumpWithSigma(10.0);
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expect(renderObject.debugLayer, same(originalLayer));
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});
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testWidgets('Image filter - enabled and disabled', (WidgetTester tester) async {
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Future<void> pumpWithEnabledStaet(bool enabled) async {
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await tester.pumpWidget(
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RepaintBoundary(
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child: ImageFiltered(
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enabled: enabled,
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imageFilter: ImageFilter.blur(sigmaX: 5, sigmaY: 5),
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child: const Placeholder(),
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),
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),
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);
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}
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await pumpWithEnabledStaet(false);
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expect(tester.layers, isNot(contains(isA<ImageFilterLayer>())));
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await pumpWithEnabledStaet(true);
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expect(tester.layers, contains(isA<ImageFilterLayer>()));
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});
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}
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