From a116bf679a8d595f4731131e46487310da6b501b Mon Sep 17 00:00:00 2001
From: Harry Terkelsen <het@google.com>
Date: Tue, 26 Mar 2024 16:31:27 -0700
Subject: [PATCH] Fix color filter for dst and dstIn

---
 .../src/engine/canvaskit/color_filter.dart    | 13 +++----
 .../canvaskit/color_filter_golden_test.dart   | 39 ++++++++++++++++++-
 2 files changed, 44 insertions(+), 8 deletions(-)

diff --git a/lib/web_ui/lib/src/engine/canvaskit/color_filter.dart b/lib/web_ui/lib/src/engine/canvaskit/color_filter.dart
index 8114aa3cedc01..569a48edb9552 100644
--- a/lib/web_ui/lib/src/engine/canvaskit/color_filter.dart
+++ b/lib/web_ui/lib/src/engine/canvaskit/color_filter.dart
@@ -100,18 +100,17 @@ Float32List _computeIdentityTransform() {
   return result;
 }
 
-SkColorFilter createSkColorFilterFromColorAndBlendMode(ui.Color color, ui.BlendMode blendMode) {
-  /// Return the identity matrix when the color opacity is 0. Replicates
-  /// effect of applying no filter
-  if (color.opacity == 0) {
-    return canvasKit.ColorFilter.MakeMatrix(_identityTransform);
-  }
+SkColorFilter createSkColorFilterFromColorAndBlendMode(
+    ui.Color color, ui.BlendMode blendMode) {
   final SkColorFilter? filter = canvasKit.ColorFilter.MakeBlend(
     toSharedSkColor1(color),
     toSkBlendMode(blendMode),
   );
   if (filter == null) {
-    throw ArgumentError('Invalid parameters for blend mode ColorFilter');
+    // If CanvasKit returns null, then the ColorFilter with this combination of
+    // color and blend mode is a no-op. So just return a dummy color filter that
+    // does nothing.
+    return canvasKit.ColorFilter.MakeMatrix(_identityTransform);
   }
   return filter;
 }
diff --git a/lib/web_ui/test/canvaskit/color_filter_golden_test.dart b/lib/web_ui/test/canvaskit/color_filter_golden_test.dart
index 48045ad942652..cf5ba125bbe18 100644
--- a/lib/web_ui/test/canvaskit/color_filter_golden_test.dart
+++ b/lib/web_ui/test/canvaskit/color_filter_golden_test.dart
@@ -156,7 +156,44 @@ void testMain() {
 
       builder.addPicture(ui.Offset.zero, redCircle2);
 
-      await matchSceneGolden('canvaskit_transparent_colorfilter.png', builder.build(), region: region);
+      await matchSceneGolden(
+          'canvaskit_transparent_colorfilter.png', builder.build(),
+          region: region);
+    });
+
+    test('ColorFilter with dst blend mode', () async {
+      final LayerSceneBuilder builder = LayerSceneBuilder();
+      builder.pushOffset(0, 0);
+      final CkPictureRecorder recorder = CkPictureRecorder();
+      final CkCanvas canvas = recorder.beginRecording(region);
+
+      canvas.drawCircle(
+        const ui.Offset(75, 125),
+        50,
+        CkPaint()..color = const ui.Color.fromARGB(255, 255, 0, 0),
+      );
+      final CkPicture redCircle1 = recorder.endRecording();
+      builder.addPicture(ui.Offset.zero, redCircle1);
+
+      // Push dst color filter
+      builder.pushColorFilter(
+          const ui.ColorFilter.mode(ui.Color(0xffff0000), ui.BlendMode.dst));
+
+      // Draw another red circle and apply it to the scene.
+      // This one should also be red with the color filter doing nothing
+      final CkPictureRecorder recorder2 = CkPictureRecorder();
+      final CkCanvas canvas2 = recorder2.beginRecording(region);
+      canvas2.drawCircle(
+        const ui.Offset(425, 125),
+        50,
+        CkPaint()..color = const ui.Color.fromARGB(255, 255, 0, 0),
+      );
+      final CkPicture redCircle2 = recorder2.endRecording();
+
+      builder.addPicture(ui.Offset.zero, redCircle2);
+
+      await matchSceneGolden('canvaskit_dst_colorfilter.png', builder.build(),
+          region: region);
     });
     // TODO(hterkelsen): https://github.com/flutter/flutter/issues/71520
   }, skip: isSafari || isFirefox);