[Impeller] Make transparent fills have no coverage (flutter#34055)

Author: bdero

impeller/entity/contents/solid_color_contents.cc

@@ -35,6 +35,9 @@ void SolidColorContents::SetCover(bool cover) {
 
 std::optional<Rect> SolidColorContents::GetCoverage(
     const Entity& entity) const {
+  if (color_.IsTransparent()) {
+    return std::nullopt;
+  }
   return path_.GetTransformedBoundingBox(entity.GetTransformation());
 };
 
@@ -60,10 +63,6 @@ VertexBuffer SolidColorContents::CreateSolidFillVertices(const Path& path,
 bool SolidColorContents::Render(const ContentContext& renderer,
                                 const Entity& entity,
                                 RenderPass& pass) const {
-  if (color_.IsTransparent()) {
-    return true;
-  }
-
   using VS = SolidFillPipeline::VertexShader;
 
   Command cmd;

impeller/entity/contents/solid_stroke_contents.cc

@@ -35,6 +35,10 @@ void SolidStrokeContents::SetPath(Path path) {
 
 std::optional<Rect> SolidStrokeContents::GetCoverage(
     const Entity& entity) const {
+  if (color_.IsTransparent()) {
+    return std::nullopt;
+  }
+
   auto path_bounds = path_.GetBoundingBox();
   if (!path_bounds.has_value()) {
     return std::nullopt;
@@ -173,7 +177,7 @@ static VertexBuffer CreateSolidStrokeVertices(
 bool SolidStrokeContents::Render(const ContentContext& renderer,
                                  const Entity& entity,
                                  RenderPass& pass) const {
-  if (color_.IsTransparent() || stroke_size_ <= 0.0) {
+  if (stroke_size_ <= 0.0) {
     return true;
   }
 

impeller/entity/contents/texture_contents.cc

@@ -4,6 +4,8 @@
 
 #include "texture_contents.h"
 
+#include <optional>
+
 #include "impeller/entity/contents/content_context.h"
 #include "impeller/entity/entity.h"
 #include "impeller/entity/texture_fill.frag.h"
@@ -35,6 +37,9 @@ void TextureContents::SetOpacity(Scalar opacity) {
 }
 
 std::optional<Rect> TextureContents::GetCoverage(const Entity& entity) const {
+  if (opacity_ == 0) {
+    return std::nullopt;
+  }
   return path_.GetTransformedBoundingBox(entity.GetTransformation());
 };
 

impeller/entity/entity_unittests.cc

@@ -925,6 +925,7 @@ TEST_P(EntityTest, SolidStrokeCoverageIsCorrect) {
     contents->SetStrokeCap(SolidStrokeContents::Cap::kButt);
     contents->SetStrokeJoin(SolidStrokeContents::Join::kBevel);
     contents->SetStrokeSize(4);
+    contents->SetColor(Color::Black());
     entity.SetContents(std::move(contents));
     auto actual = entity.GetCoverage();
     auto expected = Rect::MakeLTRB(-2, -2, 12, 12);
@@ -940,6 +941,7 @@ TEST_P(EntityTest, SolidStrokeCoverageIsCorrect) {
     contents->SetStrokeCap(SolidStrokeContents::Cap::kSquare);
     contents->SetStrokeJoin(SolidStrokeContents::Join::kBevel);
     contents->SetStrokeSize(4);
+    contents->SetColor(Color::Black());
     entity.SetContents(std::move(contents));
     auto actual = entity.GetCoverage();
     auto expected =
@@ -957,6 +959,7 @@ TEST_P(EntityTest, SolidStrokeCoverageIsCorrect) {
     contents->SetStrokeJoin(SolidStrokeContents::Join::kMiter);
     contents->SetStrokeSize(4);
     contents->SetStrokeMiter(2);
+    contents->SetColor(Color::Black());
     entity.SetContents(std::move(contents));
     auto actual = entity.GetCoverage();
     auto expected = Rect::MakeLTRB(-4, -4, 14, 14);
@@ -1011,5 +1014,47 @@ TEST_P(EntityTest, DrawVerticesSolidColorTrianglesWithoutIndex) {
   ASSERT_TRUE(OpenPlaygroundHere(e));
 }
 
+TEST_P(EntityTest, SolidFillCoverageIsCorrect) {
+  // No transform
+  {
+    auto fill = std::make_shared<SolidColorContents>();
+    fill->SetColor(Color::CornflowerBlue());
+    auto expected = Rect::MakeLTRB(100, 110, 200, 220);
+    fill->SetPath(PathBuilder{}.AddRect(expected).TakePath());
+
+    auto coverage = fill->GetCoverage({});
+    ASSERT_TRUE(coverage.has_value());
+    ASSERT_RECT_NEAR(coverage.value(), expected);
+  }
+
+  // Entity transform
+  {
+    auto fill = std::make_shared<SolidColorContents>();
+    fill->SetColor(Color::CornflowerBlue());
+    fill->SetPath(
+        PathBuilder{}.AddRect(Rect::MakeLTRB(100, 110, 200, 220)).TakePath());
+
+    Entity entity;
+    entity.SetTransformation(Matrix::MakeTranslation(Vector2(4, 5)));
+    entity.SetContents(std::move(fill));
+
+    auto coverage = entity.GetCoverage();
+    auto expected = Rect::MakeLTRB(104, 115, 204, 225);
+    ASSERT_TRUE(coverage.has_value());
+    ASSERT_RECT_NEAR(coverage.value(), expected);
+  }
+
+  // No coverage for fully transparent colors
+  {
+    auto fill = std::make_shared<SolidColorContents>();
+    fill->SetColor(Color::WhiteTransparent());
+    fill->SetPath(
+        PathBuilder{}.AddRect(Rect::MakeLTRB(100, 110, 200, 220)).TakePath());
+
+    auto coverage = fill->GetCoverage({});
+    ASSERT_FALSE(coverage.has_value());
+  }
+}
+
 }  // namespace testing
 }  // namespace impeller