Implement mask blur in display list dispatcher (flutter/engine#142)

engine/src/flutter/impeller/aiks/canvas.cc

@@ -114,7 +114,7 @@ void Canvas::DrawPath(Path path, Paint paint) {
   entity.SetPath(std::move(path));
   entity.SetStencilDepth(GetStencilDepth());
   entity.SetBlendMode(paint.blend_mode);
-  entity.SetContents(paint.CreateContentsForEntity());
+  entity.SetContents(paint.WithFilters(paint.CreateContentsForEntity()));
 
   GetCurrentPass().AddEntity(std::move(entity));
 }
@@ -242,7 +242,7 @@ void Canvas::DrawImageRect(std::shared_ptr<Image> image,
   entity.SetPath(PathBuilder{}.AddRect(dest).TakePath());
   entity.SetBlendMode(paint.blend_mode);
   entity.SetStencilDepth(GetStencilDepth());
-  entity.SetContents(contents);
+  entity.SetContents(paint.WithFilters(contents, false));
   entity.SetTransformation(GetCurrentTransformation());
 
   GetCurrentPass().AddEntity(std::move(entity));
@@ -296,7 +296,7 @@ void Canvas::DrawTextFrame(TextFrame text_frame, Point position, Paint paint) {
   entity.SetPath({});
   entity.SetStencilDepth(GetStencilDepth());
   entity.SetBlendMode(paint.blend_mode);
-  entity.SetContents(std::move(text_contents));
+  entity.SetContents(paint.WithFilters(std::move(text_contents), true));
 
   GetCurrentPass().AddEntity(std::move(entity));
 }

engine/src/flutter/impeller/aiks/paint.cc

@@ -33,4 +33,24 @@ std::shared_ptr<Contents> Paint::CreateContentsForEntity() const {
   return nullptr;
 }
 
+std::shared_ptr<Contents> Paint::WithFilters(
+    std::shared_ptr<Contents> input,
+    std::optional<bool> is_solid_color) const {
+  bool is_solid_color_val = is_solid_color.value_or(!contents);
+
+  if (mask_blur.has_value()) {
+    if (is_solid_color_val) {
+      input = FilterContents::MakeGaussianBlur(
+          FilterInput::Make(input), mask_blur->sigma, mask_blur->sigma,
+          mask_blur->blur_style);
+    } else {
+      input = FilterContents::MakeBorderMaskBlur(
+          FilterInput::Make(input), mask_blur->sigma, mask_blur->sigma,
+          mask_blur->blur_style);
+    }
+  }
+
+  return input;
+}
+
 }  // namespace impeller

engine/src/flutter/impeller/aiks/paint.h

@@ -8,12 +8,18 @@
 
 #include "flutter/fml/macros.h"
 #include "impeller/entity/contents/contents.h"
+#include "impeller/entity/contents/filters/filter_contents.h"
 #include "impeller/entity/contents/solid_stroke_contents.h"
 #include "impeller/entity/entity.h"
 #include "impeller/geometry/color.h"
 
 namespace impeller {
 
+struct MaskBlur {
+  FilterContents::BlurStyle blur_style;
+  FilterContents::Sigma sigma;
+};
+
 struct Paint {
   enum class Style {
     kFill,
@@ -27,9 +33,25 @@ struct Paint {
   Scalar stroke_miter = 4.0;
   Style style = Style::kFill;
   Entity::BlendMode blend_mode = Entity::BlendMode::kSourceOver;
+  std::optional<MaskBlur> mask_blur;
   std::shared_ptr<Contents> contents;
 
   std::shared_ptr<Contents> CreateContentsForEntity() const;
+
+  /// @brief      Wrap this paint's configured filters to the given contents.
+  /// @param[in]  input           The contents to wrap with paint's filters.
+  /// @param[in]  is_solid_color  Affects mask blurring behavior. If false, use
+  ///                             the image border for mask blurring. If true,
+  ///                             do a Gaussian blur to achieve the mask
+  ///                             blurring effect for arbitrary paths. If unset,
+  ///                             use the current paint configuration to infer
+  ///                             the result.
+  /// @return     The filter-wrapped contents. If there are no filters that need
+  ///             to be wrapped for the current paint configuration, the
+  ///             original contents is returned.
+  std::shared_ptr<Contents> WithFilters(
+      std::shared_ptr<Contents> input,
+      std::optional<bool> is_solid_color = std::nullopt) const;
 };
 
 }  // namespace impeller

engine/src/flutter/impeller/display_list/display_list_dispatcher.cc

@@ -7,6 +7,7 @@
 #include <optional>
 
 #include "flutter/fml/trace_event.h"
+#include "impeller/entity/contents/filters/filter_contents.h"
 #include "impeller/entity/contents/linear_gradient_contents.h"
 #include "impeller/entity/contents/solid_stroke_contents.h"
 #include "impeller/entity/entity.h"
@@ -253,15 +254,33 @@ void DisplayListDispatcher::setPathEffect(sk_sp<SkPathEffect> effect) {
   UNIMPLEMENTED;
 }
 
+static FilterContents::BlurStyle ToBlurStyle(SkBlurStyle blur_style) {
+  switch (blur_style) {
+    case kNormal_SkBlurStyle:
+      return FilterContents::BlurStyle::kNormal;
+    case kSolid_SkBlurStyle:
+      return FilterContents::BlurStyle::kSolid;
+    case kOuter_SkBlurStyle:
+      return FilterContents::BlurStyle::kOuter;
+    case kInner_SkBlurStyle:
+      return FilterContents::BlurStyle::kInner;
+  }
+}
+
 // |flutter::Dispatcher|
 void DisplayListDispatcher::setMaskFilter(const flutter::DlMaskFilter* filter) {
   // Needs https://github.com/flutter/flutter/issues/95434
   if (filter == nullptr) {
-    // Reset everything
+    paint_.mask_blur = std::nullopt;
     return;
   }
   switch (filter->type()) {
-    case flutter::DlMaskFilterType::kBlur:
+    case flutter::DlMaskFilterType::kBlur: {
+      auto blur = filter->asBlur();
+      paint_.mask_blur = {.blur_style = ToBlurStyle(blur->style()),
+                          .sigma = FilterContents::Sigma(blur->sigma())};
+      break;
+    }
     case flutter::DlMaskFilterType::kUnknown:
       UNIMPLEMENTED;
       break;

engine/src/flutter/impeller/display_list/display_list_unittests.cc

@@ -8,6 +8,8 @@
 #include "third_party/skia/include/core/SkPathBuilder.h"
 
 #include "flutter/display_list/display_list_builder.h"
+#include "flutter/display_list/display_list_mask_filter.h"
+#include "flutter/display_list/types.h"
 #include "flutter/testing/testing.h"
 #include "impeller/display_list/display_list_image_impeller.h"
 #include "impeller/display_list/display_list_playground.h"
@@ -174,5 +176,36 @@ TEST_P(DisplayListTest, StrokedPathsDrawCorrectly) {
   ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
 }
 
+TEST_F(DisplayListTest, CanDrawWithMaskBlur) {
+  auto texture = CreateTextureForFixture("embarcadero.jpg");
+  flutter::DisplayListBuilder builder;
+
+  // Mask blurred image.
+  {
+    auto filter = flutter::DlBlurMaskFilter(kNormal_SkBlurStyle, 10.0f);
+    builder.setMaskFilter(&filter);
+    builder.drawImage(DlImageImpeller::Make(texture), SkPoint::Make(100, 100),
+                      SkSamplingOptions{}, true);
+  }
+
+  // Mask blurred filled path.
+  {
+    builder.setColor(SK_ColorYELLOW);
+    auto filter = flutter::DlBlurMaskFilter(kOuter_SkBlurStyle, 10.0f);
+    builder.setMaskFilter(&filter);
+    builder.drawArc(SkRect::MakeXYWH(410, 110, 100, 100), 45, 270, true);
+  }
+
+  // Mask blurred text.
+  {
+    auto filter = flutter::DlBlurMaskFilter(kSolid_SkBlurStyle, 10.0f);
+    builder.setMaskFilter(&filter);
+    builder.drawTextBlob(
+        SkTextBlob::MakeFromString("Testing", CreateTestFont()), 220, 170);
+  }
+
+  ASSERT_TRUE(OpenPlaygroundHere(builder.Build()));
+}
+
 }  // namespace testing
 }  // namespace impeller

engine/src/flutter/impeller/entity/contents/contents.cc

@@ -47,7 +47,7 @@ std::optional<Snapshot> Contents::RenderToSnapshot(
                                             RenderPass& pass) -> bool {
         Entity sub_entity;
         sub_entity.SetPath(entity.GetPath());
-        sub_entity.SetBlendMode(Entity::BlendMode::kSource);
+        sub_entity.SetBlendMode(Entity::BlendMode::kSourceOver);
         sub_entity.SetTransformation(
             Matrix::MakeTranslation(Vector3(-bounds->origin)) *
             entity.GetTransformation());