Implement pushColorFilter in CanvasKit (flutter/engine#22838)

* Implement pushColorFilter in CanvasKit

* Add test

* Update goldens lock

engine/src/flutter/lib/web_ui/dev/goldens_lock.yaml

@@ -1,2 +1,2 @@
 repository: https://github.com/flutter/goldens.git
-revision: ac75f12c6e93461369e1391da6cc20bf8cb08829
+revision: c808c28c81b6c3143ae969e8c49bed4a6d49aabb

engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/layer.dart

@@ -449,8 +449,8 @@ class PhysicalShapeLayer extends ContainerLayer
     assert(needsPainting);
 
     if (_elevation != 0) {
-      drawShadow(paintContext.leafNodesCanvas!, _path, _shadowColor!, _elevation,
-          _color.alpha != 0xff);
+      drawShadow(paintContext.leafNodesCanvas!, _path, _shadowColor!,
+          _elevation, _color.alpha != 0xff);
     }
 
     final CkPaint paint = CkPaint()..color = _color;
@@ -497,6 +497,25 @@ class PhysicalShapeLayer extends ContainerLayer
   }
 }
 
+/// A layer which contains a [ui.ColorFilter].
+class ColorFilterLayer extends ContainerLayer {
+  ColorFilterLayer(this.filter);
+
+  final ui.ColorFilter filter;
+
+  @override
+  void paint(PaintContext paintContext) {
+    assert(needsPainting);
+
+    CkPaint paint = CkPaint();
+    paint.colorFilter = filter;
+
+    paintContext.internalNodesCanvas.saveLayer(paintBounds, paint);
+    paintChildren(paintContext);
+    paintContext.internalNodesCanvas.restore();
+  }
+}
+
 /// A layer which renders a platform view (an HTML element in this case).
 class PlatformViewLayer extends Layer {
   PlatformViewLayer(this.viewId, this.offset, this.width, this.height);

engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/layer_scene_builder.dart

@@ -138,12 +138,13 @@ class LayerSceneBuilder implements ui.SceneBuilder {
   }
 
   @override
-  ui.ColorFilterEngineLayer pushColorFilter(
+  ui.ColorFilterEngineLayer? pushColorFilter(
     ui.ColorFilter filter, {
     ui.ColorFilterEngineLayer? oldLayer,
   }) {
     assert(filter != null); // ignore: unnecessary_null_comparison
-    throw UnimplementedError();
+    pushLayer(ColorFilterLayer(filter));
+    return null;
   }
 
   ui.ImageFilterEngineLayer? pushImageFilter(

engine/src/flutter/lib/web_ui/test/canvaskit/color_filter_golden_test.dart

@@ -0,0 +1,78 @@
+// 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.
+
+// @dart = 2.12
+import 'package:test/bootstrap/browser.dart';
+import 'package:test/test.dart';
+import 'package:ui/src/engine.dart';
+import 'package:ui/ui.dart' as ui;
+
+import 'package:web_engine_tester/golden_tester.dart';
+
+import 'common.dart';
+
+void main() {
+  internalBootstrapBrowserTest(() => testMain);
+}
+
+const ui.Rect region = const ui.Rect.fromLTRB(0, 0, 500, 250);
+
+Future<void> matchSceneGolden(String goldenFile, LayerScene scene,
+    {bool write = false}) async {
+  final EnginePlatformDispatcher dispatcher =
+      ui.window.platformDispatcher as EnginePlatformDispatcher;
+  dispatcher.rasterizer!.draw(scene.layerTree);
+  await matchGoldenFile(goldenFile, region: region, write: write);
+}
+
+void testMain() {
+  group('ColorFilter', () {
+    setUpCanvasKitTest();
+
+    test('ColorFilter.matrix applies a color filter', () async {
+      final LayerSceneBuilder builder = LayerSceneBuilder();
+
+      builder.pushOffset(0, 0);
+
+      // Draw a red circle and apply it to the scene.
+      final CkPictureRecorder recorder = CkPictureRecorder();
+      final CkCanvas canvas = recorder.beginRecording(region);
+
+      canvas.drawCircle(
+        ui.Offset(75, 125),
+        50,
+        CkPaint()..color = ui.Color.fromARGB(255, 255, 0, 0),
+      );
+      final CkPicture redCircle = recorder.endRecording();
+
+      builder.addPicture(ui.Offset.zero, redCircle);
+
+      // Apply a "greyscale" color filter.
+      builder.pushColorFilter(ui.ColorFilter.matrix([
+        0.2126, 0.7152, 0.0722, 0, 0, //
+        0.2126, 0.7152, 0.0722, 0, 0, //
+        0.2126, 0.7152, 0.0722, 0, 0, //
+        0, 0, 0, 1, 0, //
+      ]));
+
+      // Draw another red circle and apply it to the scene.
+      // This one should be grey since we have the color filter.
+      final CkPictureRecorder recorder2 = CkPictureRecorder();
+      final CkCanvas canvas2 = recorder2.beginRecording(region);
+
+      canvas2.drawCircle(
+        ui.Offset(425, 125),
+        50,
+        CkPaint()..color = ui.Color.fromARGB(255, 255, 0, 0),
+      );
+      final CkPicture greyCircle = recorder2.endRecording();
+
+      builder.addPicture(ui.Offset.zero, greyCircle);
+
+      await matchSceneGolden('canvaskit_colorfilter.png', builder.build());
+    });
+    // TODO: https://github.com/flutter/flutter/issues/60040
+    // TODO: https://github.com/flutter/flutter/issues/71520
+  }, skip: isIosSafari || isFirefox);
+}

engine/src/flutter/lib/web_ui/test/canvaskit/scene_test.dart

@@ -49,6 +49,17 @@ void testMain() {
       final ui.Image sceneImage = await scene.toImage(100, 100);
       expect(sceneImage, isA<CkImage>());
     });
-  // TODO: https://github.com/flutter/flutter/issues/60040
+
+    test('pushColorFilter does not throw', () async {
+      final ui.SceneBuilder builder = ui.SceneBuilder();
+      expect(builder, isA<LayerSceneBuilder>());
+
+      builder.pushOffset(0, 0);
+      builder.pushColorFilter(ui.ColorFilter.srgbToLinearGamma());
+
+      final ui.Scene scene = builder.build();
+      expect(scene, isNotNull);
+    });
+    // TODO: https://github.com/flutter/flutter/issues/60040
   }, skip: isIosSafari);
 }