[CP] [Impeller] Limit blur kernel to 1000x1000 pixels (#42154) (#42217)

CP for #42154

Author: bdero

impeller/aiks/aiks_unittests.cc

@@ -1951,6 +1951,22 @@ TEST_P(AiksTest, CanRenderTinyOverlappingSubpasses) {
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
 }
 
+TEST_P(AiksTest, CanRenderBackdropBlurHugeSigma) {
+  Canvas canvas;
+  canvas.DrawCircle({400, 400}, 300, {.color = Color::Green()});
+  canvas.SaveLayer({.blend_mode = BlendMode::kSource}, std::nullopt,
+                   [](const FilterInput::Ref& input,
+                      const Matrix& effect_transform, bool is_subpass) {
+                     return FilterContents::MakeGaussianBlur(
+                         input, Sigma(999999), Sigma(999999),
+                         FilterContents::BlurStyle::kNormal,
+                         Entity::TileMode::kClamp, effect_transform);
+                   });
+  canvas.Restore();
+
+  ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
+}
+
 // Regression test for https://github.com/flutter/flutter/issues/126701 .
 TEST_P(AiksTest, CanRenderClippedRuntimeEffects) {
   if (GetParam() != PlaygroundBackend::kMetal) {

impeller/entity/contents/filters/gaussian_blur_filter_contents.cc

@@ -98,6 +98,8 @@ std::optional<Entity> DirectionalGaussianBlurFilterContents::RenderFilter(
     return std::nullopt;
   }
 
+  // Limit the kernel size to 1000x1000 pixels, like Skia does.
+  auto radius = std::min(Radius{blur_sigma_}.radius, 500.0f);
   // Input 0 snapshot.
 
   auto input_snapshot = inputs[0]->GetSnapshot(renderer, entity);
@@ -111,8 +113,6 @@ std::optional<Entity> DirectionalGaussianBlurFilterContents::RenderFilter(
         entity.GetStencilDepth());  // No blur to render.
   }
 
-  auto radius = Radius{blur_sigma_}.radius;
-
   auto transform = entity.GetTransformation() * effect_transform.Basis();
   auto transformed_blur_radius =
       transform.TransformDirection(blur_direction_ * radius);
@@ -337,7 +337,7 @@ std::optional<Rect> DirectionalGaussianBlurFilterContents::GetFilterCoverage(
 
   auto transform = inputs[0]->GetTransform(entity) * effect_transform.Basis();
   auto transformed_blur_vector =
-      transform.TransformDirection(blur_direction_* Radius{blur_sigma_}.radius)
+      transform.TransformDirection(blur_direction_ * Radius{blur_sigma_}.radius)
           .Abs();
   auto extent = coverage->size + transformed_blur_vector * 2;
   return Rect(coverage->origin - transformed_blur_vector,