[web] implement pushImageFilter

ci/licenses_golden/licenses_flutter

@@ -452,6 +452,7 @@ FILE: ../../../flutter/lib/web_ui/lib/src/engine/shadow.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/surface/backdrop_filter.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/surface/clip.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/surface/debug_canvas_reuse_overlay.dart
+FILE: ../../../flutter/lib/web_ui/lib/src/engine/surface/image_filter.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/surface/offset.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/surface/opacity.dart
 FILE: ../../../flutter/lib/web_ui/lib/src/engine/surface/painting.dart

lib/web_ui/dev/goldens_lock.yaml

@@ -1,2 +1,2 @@
 repository: https://github.com/flutter/goldens.git
-revision: ab1f2da642d6c5188b312965759ce7157fd073b9
+revision: a121ff1169a1b478274a3e34c95d0a1d2d685948

lib/web_ui/lib/src/engine.dart

@@ -88,6 +88,7 @@ part 'engine/shadow.dart';
 part 'engine/surface/backdrop_filter.dart';
 part 'engine/surface/clip.dart';
 part 'engine/surface/debug_canvas_reuse_overlay.dart';
+part 'engine/surface/image_filter.dart';
 part 'engine/surface/offset.dart';
 part 'engine/surface/opacity.dart';
 part 'engine/surface/painting.dart';

lib/web_ui/lib/src/engine/compositor/layer.dart

@@ -343,6 +343,23 @@ class TransformLayer extends ContainerLayer
   }
 }
 
+/// A layer that applies an [ui.ImageFilter] to its children.
+class ImageFilterLayer extends ContainerLayer implements ui.OpacityEngineLayer {
+  ImageFilterLayer(this._filter);
+
+  final ui.ImageFilter _filter;
+
+  @override
+  void paint(PaintContext paintContext) {
+    assert(needsPainting);
+    final ui.Paint paint = ui.Paint();
+    paint.imageFilter = _filter;
+    paintContext.internalNodesCanvas.saveLayer(paintBounds, paint);
+    paintChildren(paintContext);
+    paintContext.internalNodesCanvas.restore();
+  }
+}
+
 /// A layer containing a [Picture].
 class PictureLayer extends Layer {
   /// The picture to paint into the canvas.

lib/web_ui/lib/src/engine/compositor/layer_scene_builder.dart

@@ -147,7 +147,8 @@ class LayerSceneBuilder implements ui.SceneBuilder {
     ui.ImageFilterEngineLayer oldLayer,
   }) {
     assert(filter != null);
-    throw UnimplementedError();
+    pushLayer(ImageFilterLayer(filter));
+    return null;
   }
 
   @override

lib/web_ui/lib/src/engine/surface/backdrop_filter.dart

@@ -10,7 +10,7 @@ class PersistedBackdropFilter extends PersistedContainerSurface
   PersistedBackdropFilter(PersistedBackdropFilter oldLayer, this.filter)
       : super(oldLayer);
 
-  final ui.ImageFilter filter;
+  final EngineImageFilter filter;
 
   /// The dedicated child container element that's separate from the
   /// [rootElement] is used to host child in front of [filterElement] that
@@ -24,10 +24,6 @@ class PersistedBackdropFilter extends PersistedContainerSurface
   // Reference to transform last used to cache [_invertedTransform].
   Matrix4 _previousTransform;
 
-  @override
-  Matrix4 get localTransformInverse =>
-      _localTransformInverse ??= Matrix4.identity();
-
   @override
   void adoptElements(PersistedBackdropFilter oldSurface) {
     super.adoptElements(oldSurface);
@@ -85,12 +81,10 @@ class PersistedBackdropFilter extends PersistedContainerSurface
         ..backgroundColor = '#000'
         ..opacity = '0.2';
     } else {
-      final EngineImageFilter engineFilter = filter;
       // CSS uses pixel radius for blur. Flutter & SVG use sigma parameters. For
       // Gaussian blur with standard deviation (normal distribution),
       // the blur will fall within 2 * sigma pixels.
-      domRenderer.setElementStyle(_filterElement, 'backdrop-filter',
-          'blur(${math.max(engineFilter.sigmaX, engineFilter.sigmaY) * 2}px)');
+      domRenderer.setElementStyle(_filterElement, 'backdrop-filter', _imageFilterToCss(filter));
     }
   }
 

lib/web_ui/lib/src/engine/surface/clip.dart

@@ -71,10 +71,6 @@ class PersistedClipRect extends PersistedContainerSurface
     _projectedClip = null;
   }
 
-  @override
-  Matrix4 get localTransformInverse =>
-      _localTransformInverse ??= Matrix4.identity();
-
   @override
   html.Element createElement() {
     return super.createElement()..setAttribute('clip-type', 'rect');
@@ -122,10 +118,6 @@ class PersistedClipRRect extends PersistedContainerSurface
     _projectedClip = null;
   }
 
-  @override
-  Matrix4 get localTransformInverse =>
-      _localTransformInverse ??= Matrix4.identity();
-
   @override
   html.Element createElement() {
     return super.createElement()..setAttribute('clip-type', 'rrect');
@@ -193,10 +185,6 @@ class PersistedPhysicalShape extends PersistedContainerSurface
     _projectedClip = null;
   }
 
-  @override
-  Matrix4 get localTransformInverse =>
-      _localTransformInverse ??= Matrix4.identity();
-
   void _applyColor() {
     rootElement.style.backgroundColor = color.toCssString();
   }
@@ -350,10 +338,6 @@ class PersistedClipPath extends PersistedContainerSurface
     _localClipBounds ??= clipPath.getBounds();
   }
 
-  @override
-  Matrix4 get localTransformInverse =>
-      _localTransformInverse ??= Matrix4.identity();
-
   @override
   void apply() {
     if (clipPath == null) {

lib/web_ui/lib/src/engine/surface/image_filter.dart

@@ -0,0 +1,32 @@
+// Copyright 2013 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.
+
+part of engine;
+
+/// A surface that applies an [imageFilter] to its children.
+class PersistedImageFilter extends PersistedContainerSurface
+    implements ui.ImageFilterEngineLayer {
+  PersistedImageFilter(PersistedImageFilter oldLayer, this.filter) : super(oldLayer);
+
+  final ui.ImageFilter filter;
+
+  @override
+  html.Element createElement() {
+    return defaultCreateElement('flt-image-filter');
+  }
+
+  @override
+  void apply() {
+    rootElement.style.filter = _imageFilterToCss(filter);
+  }
+
+  @override
+  void update(PersistedImageFilter oldSurface) {
+    super.update(oldSurface);
+
+    if (oldSurface.filter != filter) {
+      apply();
+    }
+  }
+}

lib/web_ui/lib/src/engine/surface/picture.dart

@@ -100,10 +100,6 @@ class PersistedHoudiniPicture extends PersistedPicture {
     return existingSurface.picture == picture ? 0.0 : 1.0;
   }
 
-  @override
-  Matrix4 get localTransformInverse =>
-      _localTransformInverse ??= Matrix4.identity();
-
   static void _registerCssPainter() {
     _cssPainterRegistered = true;
     final dynamic css = js_util.getProperty(html.window, 'CSS');

lib/web_ui/lib/src/engine/surface/scene_builder.dart

@@ -189,7 +189,7 @@ class SurfaceSceneBuilder implements ui.SceneBuilder {
     ui.ImageFilterEngineLayer oldLayer,
   }) {
     assert(filter != null);
-    throw UnimplementedError();
+    return _pushSurface(PersistedImageFilter(oldLayer, filter));
   }
 
   /// Pushes a backdrop filter operation onto the operation stack.
@@ -537,3 +537,10 @@ class SurfaceSceneBuilder implements ui.SceneBuilder {
     throw UnimplementedError();
   }
 }
+
+// TODO(yjbanov): in HTML the blur looks too aggressive. The current
+//                implementation was copied from the existing backdrop-filter
+//                but probably needs a revision.
+String _imageFilterToCss(EngineImageFilter filter) {
+  return 'blur(${math.max(filter.sigmaX, filter.sigmaY) * 2}px)';
+}

lib/web_ui/lib/src/engine/surface/surface.dart

@@ -804,7 +804,12 @@ abstract class PersistedSurface implements ui.EngineLayer {
   // Matrix only contains local transform (not chain multiplied since root).
   Matrix4 _localTransformInverse;
 
-  Matrix4 get localTransformInverse;
+  /// The inverse of the local transform that this surface applies to its children.
+  ///
+  /// The default implementation is identity transform. Concrete
+  /// implementations may override this getter to supply a different transform.
+  Matrix4 get localTransformInverse =>
+      _localTransformInverse ??= Matrix4.identity();
 
   /// Recomputes [transform] and [globalClip] fields.
   ///

lib/web_ui/test/golden_tests/engine/compositing_golden_test.dart

@@ -98,6 +98,19 @@ void main() async {
     await matchGoldenFile('compositing_shifted_physical_shape_clip.png', region: region);
   }, timeout: const Timeout(Duration(seconds: 10)));
 
+  test('pushImageFilter', () async {
+    final SurfaceSceneBuilder builder = SurfaceSceneBuilder();
+    builder.pushImageFilter(
+      ImageFilter.blur(sigmaX: 1, sigmaY: 3),
+    );
+    _drawTestPicture(builder);
+    builder.pop();
+
+    html.document.body.append(builder.build().webOnlyRootElement);
+
+    await matchGoldenFile('compositing_image_filter.png', region: region);
+  }, timeout: const Timeout(Duration(seconds: 10)));
+
   group('Cull rect computation', () {
     _testCullRectComputation();
   });