fixes mask blurs on stoked gradient geometry (#55717)

fixes flutter/flutter#155930

This starts taking into account the translation of the entity that is
snapshotted when performing the gaussian blur. I'm uncertain under what
conditions, but sometimes the snapshot logic would need this offset. The
linked issue and added tests demonstrate those cases.

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Author: gaaclarke

impeller/display_list/aiks_dl_blur_unittests.cc

@@ -60,6 +60,72 @@ TEST_P(AiksTest, SolidColorOvalsMaskBlurTinySigma) {
   ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
 }
 
+sk_sp<flutter::DisplayList> DoGradientOvalStrokeMaskBlur(Vector2 content_Scale,
+                                                         Scalar sigma,
+                                                         DlBlurStyle style) {
+  DisplayListBuilder builder;
+  builder.Scale(content_Scale.x, content_Scale.y);
+
+  DlPaint background_paint;
+  background_paint.setColor(DlColor(1, 0.1, 0.1, 0.1, DlColorSpace::kSRGB));
+  builder.DrawPaint(background_paint);
+
+  std::vector<DlColor> colors = {DlColor::kRed(), DlColor::kBlue()};
+  std::vector<Scalar> stops = {0.0, 1.0};
+
+  DlPaint paint;
+  paint.setMaskFilter(DlBlurMaskFilter::Make(style, sigma));
+  auto gradient = DlColorSource::MakeLinear(
+      {0, 0}, {200, 200}, 2, colors.data(), stops.data(), DlTileMode::kClamp);
+  paint.setColorSource(gradient);
+  paint.setColor(DlColor::kWhite());
+  paint.setDrawStyle(DlDrawStyle::kStroke);
+  paint.setStrokeWidth(20);
+
+  builder.Save();
+  builder.Translate(100, 100);
+
+  {
+    DlPaint line_paint;
+    line_paint.setColor(DlColor::kWhite());
+    builder.DrawLine({100, 0}, {100, 60}, line_paint);
+    builder.DrawLine({0, 30}, {200, 30}, line_paint);
+  }
+
+  SkRRect rrect =
+      SkRRect::MakeRectXY(SkRect::MakeXYWH(0, 0, 200.0f, 60.0f), 50, 100);
+  builder.DrawRRect(rrect, paint);
+  builder.Restore();
+
+  return builder.Build();
+}
+
+// https://github.com/flutter/flutter/issues/155930
+TEST_P(AiksTest, GradientOvalStrokeMaskBlur) {
+  ASSERT_TRUE(OpenPlaygroundHere(DoGradientOvalStrokeMaskBlur(
+      GetContentScale(), /*sigma=*/10, DlBlurStyle::kNormal)));
+}
+
+TEST_P(AiksTest, GradientOvalStrokeMaskBlurSigmaZero) {
+  ASSERT_TRUE(OpenPlaygroundHere(DoGradientOvalStrokeMaskBlur(
+      GetContentScale(), /*sigma=*/0, DlBlurStyle::kNormal)));
+}
+
+TEST_P(AiksTest, GradientOvalStrokeMaskBlurOuter) {
+  ASSERT_TRUE(OpenPlaygroundHere(DoGradientOvalStrokeMaskBlur(
+      GetContentScale(), /*sigma=*/10, DlBlurStyle::kOuter)));
+}
+
+TEST_P(AiksTest, GradientOvalStrokeMaskBlurInner) {
+  ASSERT_TRUE(OpenPlaygroundHere(DoGradientOvalStrokeMaskBlur(
+      GetContentScale(), /*sigma=*/10, DlBlurStyle::kInner)));
+}
+
+TEST_P(AiksTest, GradientOvalStrokeMaskBlurSolid) {
+  ASSERT_TRUE(OpenPlaygroundHere(DoGradientOvalStrokeMaskBlur(
+      GetContentScale(), /*sigma=*/10, DlBlurStyle::kSolid)));
+}
+
 TEST_P(AiksTest, SolidColorCircleMaskBlurTinySigma) {
   DisplayListBuilder builder;
   builder.Scale(GetContentScale().x, GetContentScale().y);

impeller/display_list/aiks_dl_text_unittests.cc

@@ -300,6 +300,7 @@ TEST_P(AiksTest, CanRenderEmojiTextFrame) {
 TEST_P(AiksTest, CanRenderEmojiTextFrameWithBlur) {
   DisplayListBuilder builder;
 
+  builder.Scale(GetContentScale().x, GetContentScale().y);
   DlPaint paint;
   paint.setColor(DlColor::ARGB(1, 0.1, 0.1, 0.1));
   builder.DrawPaint(paint);

impeller/entity/contents/filters/gaussian_blur_filter_contents.cc

@@ -74,6 +74,9 @@ Vector2 ExtractScale(const Matrix& matrix) {
 struct BlurInfo {
   /// The scalar that is used to get from source space to unrotated local space.
   Vector2 source_space_scalar;
+  /// The translation that is used to get from  source space to unrotated local
+  /// space.
+  Vector2 source_space_offset;
   /// Sigma when considering an entity's scale and the effect transform.
   Vector2 scaled_sigma;
   /// Blur radius in source pixels based on scaled_sigma.
@@ -95,6 +98,8 @@ BlurInfo CalculateBlurInfo(const Entity& entity,
   // applied to the result of the blur as part of the result's transform.
   const Vector2 source_space_scalar =
       ExtractScale(entity.GetTransform().Basis());
+  const Vector2 source_space_offset =
+      Vector2(entity.GetTransform().m[12], entity.GetTransform().m[13]);
 
   Vector2 scaled_sigma =
       (effect_transform.Basis() * Matrix::MakeScale(source_space_scalar) *  //
@@ -110,6 +115,7 @@ BlurInfo CalculateBlurInfo(const Entity& entity,
       (Matrix::MakeScale(source_space_scalar) * padding).Abs();
   return {
       .source_space_scalar = source_space_scalar,
+      .source_space_offset = source_space_offset,
       .scaled_sigma = scaled_sigma,
       .blur_radius = blur_radius,
       .padding = padding,
@@ -545,7 +551,8 @@ Entity ApplyBlurStyle(FilterContents::BlurStyle blur_style,
                       const Snapshot& input_snapshot,
                       Entity blur_entity,
                       const Geometry* geometry,
-                      Vector2 source_space_scalar) {
+                      Vector2 source_space_scalar,
+                      Vector2 source_space_offset) {
   switch (blur_style) {
     case FilterContents::BlurStyle::kNormal:
       return blur_entity;
@@ -563,9 +570,11 @@ Entity ApplyBlurStyle(FilterContents::BlurStyle blur_style,
           Entity::FromSnapshot(input_snapshot, entity.GetBlendMode());
       Entity result;
       Matrix blurred_transform = blur_entity.GetTransform();
-      Matrix snapshot_transform = entity.GetTransform() *  //
-                                  Matrix::MakeScale(1.f / source_space_scalar) *
-                                  input_snapshot.transform;
+      Matrix snapshot_transform =
+          entity.GetTransform() *  //
+          Matrix::MakeScale(1.f / source_space_scalar) *
+          Matrix::MakeTranslation(-1 * source_space_offset) *
+          input_snapshot.transform;
       result.SetContents(Contents::MakeAnonymous(
           fml::MakeCopyable([blur_entity = blur_entity.Clone(),
                              blurred_transform, snapshot_transform,
@@ -697,11 +706,13 @@ std::optional<Entity> GaussianBlurFilterContents::RenderFilter(
 
   Entity snapshot_entity = entity.Clone();
   snapshot_entity.SetTransform(
+      Matrix::MakeTranslation(blur_info.source_space_offset) *
       Matrix::MakeScale(blur_info.source_space_scalar));
 
   std::optional<Rect> source_expanded_coverage_hint;
   if (expanded_coverage_hint.has_value()) {
     source_expanded_coverage_hint = expanded_coverage_hint->TransformBounds(
+        Matrix::MakeTranslation(blur_info.source_space_offset) *
         Matrix::MakeScale(blur_info.source_space_scalar) *
         entity.GetTransform().Invert());
   }
@@ -717,9 +728,11 @@ std::optional<Entity> GaussianBlurFilterContents::RenderFilter(
     Entity result =
         Entity::FromSnapshot(input_snapshot.value(),
                              entity.GetBlendMode());  // No blur to render.
-    result.SetTransform(entity.GetTransform() *
-                        Matrix::MakeScale(1.f / blur_info.source_space_scalar) *
-                        input_snapshot->transform);
+    result.SetTransform(
+        entity.GetTransform() *
+        Matrix::MakeScale(1.f / blur_info.source_space_scalar) *
+        Matrix::MakeTranslation(-1 * blur_info.source_space_offset) *
+        input_snapshot->transform);
     return result;
   }
 
@@ -827,15 +840,17 @@ std::optional<Entity> GaussianBlurFilterContents::RenderFilter(
                .transform =
                    entity.GetTransform() *                                   //
                    Matrix::MakeScale(1.f / blur_info.source_space_scalar) *  //
-                   downsample_pass_args.transform *                          //
+                   Matrix::MakeTranslation(-1 * blur_info.source_space_offset) *
+                   downsample_pass_args.transform *  //
                    Matrix::MakeScale(1 / downsample_pass_args.effective_scalar),
                .sampler_descriptor = sampler_desc,
                .opacity = input_snapshot->opacity},
       entity.GetBlendMode());
 
   return ApplyBlurStyle(mask_blur_style_, entity, inputs[0],
                         input_snapshot.value(), std::move(blur_output_entity),
-                        mask_geometry_, blur_info.source_space_scalar);
+                        mask_geometry_, blur_info.source_space_scalar,
+                        blur_info.source_space_offset);
 }
 
 Scalar GaussianBlurFilterContents::CalculateBlurRadius(Scalar sigma) {

testing/impeller_golden_tests_output.txt

@@ -718,6 +718,21 @@ impeller_Play_AiksTest_GaussianBlurStyleSolid_Metal.png
 impeller_Play_AiksTest_GaussianBlurStyleSolid_OpenGLES.png
 impeller_Play_AiksTest_GaussianBlurStyleSolid_Vulkan.png
 impeller_Play_AiksTest_GaussianBlurWithoutDecalSupport_Metal.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurInner_Metal.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurInner_OpenGLES.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurInner_Vulkan.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurOuter_Metal.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurOuter_OpenGLES.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurOuter_Vulkan.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurSigmaZero_Metal.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurSigmaZero_OpenGLES.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurSigmaZero_Vulkan.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurSolid_Metal.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurSolid_OpenGLES.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlurSolid_Vulkan.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlur_Metal.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlur_OpenGLES.png
+impeller_Play_AiksTest_GradientOvalStrokeMaskBlur_Vulkan.png
 impeller_Play_AiksTest_GradientStrokesRenderCorrectly_Metal.png
 impeller_Play_AiksTest_GradientStrokesRenderCorrectly_OpenGLES.png
 impeller_Play_AiksTest_GradientStrokesRenderCorrectly_Vulkan.png