[Impeller] Fix framebuffer blend UVs.

impeller/aiks/aiks_unittests.cc

@@ -1608,6 +1608,26 @@ TEST_P(AiksTest, DrawPaintWithAdvancedBlendOverFilter) {
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
 }
 
+TEST_P(AiksTest, DrawAdvancedBlendPartlyOffscreen) {
+  std::vector<Color> colors = {Color{0.9568, 0.2627, 0.2118, 1.0},
+                               Color{0.1294, 0.5882, 0.9529, 1.0}};
+  std::vector<Scalar> stops = {0.0, 1.0};
+
+  Paint paint = {
+      .color_source = ColorSource::MakeLinearGradient(
+          {0, 0}, {100, 100}, std::move(colors), std::move(stops),
+          Entity::TileMode::kRepeat, Matrix::MakeScale(Vector3(0.3, 0.3, 0.3))),
+      .blend_mode = BlendMode::kLighten,
+  };
+
+  Canvas canvas;
+  canvas.DrawPaint({.color = Color::Blue()});
+  canvas.Scale(Vector2(2, 2));
+  canvas.ClipRect(Rect::MakeLTRB(0, 0, 200, 200));
+  canvas.DrawCircle({100, 100}, 100, paint);
+  ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
+}
+
 #define BLEND_MODE_TUPLE(blend_mode) {#blend_mode, BlendMode::k##blend_mode},
 
 struct BlendModeSelection {

impeller/entity/contents/framebuffer_blend_contents.cc

@@ -48,6 +48,7 @@ bool FramebufferBlendContents::Render(const ContentContext& renderer,
       std::nullopt,                                // sampler_descriptor
       true,                                        // msaa_enabled
       "FramebufferBlendContents Snapshot");        // label
+
   if (!src_snapshot.has_value()) {
     return true;
   }
@@ -56,21 +57,16 @@ bool FramebufferBlendContents::Render(const ContentContext& renderer,
     return true;
   }
   Rect src_coverage = coverage.value();
-  auto maybe_src_uvs = src_snapshot->GetCoverageUVs(src_coverage);
-  if (!maybe_src_uvs.has_value()) {
-    return true;
-  }
-  std::array<Point, 4> src_uvs = maybe_src_uvs.value();
 
   auto size = src_coverage.size;
   VertexBufferBuilder<VS::PerVertexData> vtx_builder;
   vtx_builder.AddVertices({
-      {Point(0, 0), src_uvs[0]},
-      {Point(size.width, 0), src_uvs[1]},
-      {Point(size.width, size.height), src_uvs[3]},
-      {Point(0, 0), src_uvs[0]},
-      {Point(size.width, size.height), src_uvs[3]},
-      {Point(0, size.height), src_uvs[2]},
+      {Point(0, 0), Point(0, 0)},
+      {Point(size.width, 0), Point(1, 0)},
+      {Point(size.width, size.height), Point(1, 1)},
+      {Point(0, 0), Point(0, 0)},
+      {Point(size.width, size.height), Point(1, 1)},
+      {Point(0, size.height), Point(0, 1)},
   });
   auto vtx_buffer = vtx_builder.CreateVertexBuffer(host_buffer);
 
@@ -147,8 +143,7 @@ bool FramebufferBlendContents::Render(const ContentContext& renderer,
   FS::BindTextureSamplerSrc(cmd, src_snapshot->texture, src_sampler);
 
   frame_info.mvp = Matrix::MakeOrthographic(pass.GetRenderTargetSize()) *
-                   entity.GetTransformation() *
-                   Matrix::MakeTranslation(src_coverage.origin);
+                   src_snapshot->transform;
   frame_info.src_y_coord_scale = src_snapshot->texture->GetYCoordScale();
   VS::BindFrameInfo(cmd, host_buffer.EmplaceUniform(frame_info));