Reapply "[Impeller] new blur: refactored math and fixed expanded padding size (#49206)"

This reverts commit 8b9a0bb.

Author: gaaclarke

impeller/aiks/aiks_unittests.cc

@@ -3976,6 +3976,5 @@ TEST_P(AiksTest, SubpassWithClearColorOptimization) {
   // will be filled with NaNs and may produce a magenta texture on macOS or iOS.
   ASSERT_TRUE(OpenPlaygroundHere(canvas.EndRecordingAsPicture()));
 }
-
 }  // namespace testing
 }  // namespace impeller

impeller/entity/contents/filters/gaussian_blur_filter_contents.cc

@@ -19,16 +19,6 @@ using GaussianBlurFragmentShader = GaussianBlurPipeline::FragmentShader;
 
 namespace {
 
-std::optional<Rect> ExpandCoverageHint(const std::optional<Rect>& coverage_hint,
-                                       const Matrix& source_to_local_transform,
-                                       const Vector2& padding) {
-  if (!coverage_hint.has_value()) {
-    return std::nullopt;
-  }
-  Vector2 transformed_padding = (source_to_local_transform * padding).Abs();
-  return coverage_hint->Expand(transformed_padding);
-}
-
 SamplerDescriptor MakeSamplerDescriptor(MinMagFilter filter,
                                         SamplerAddressMode address_mode) {
   SamplerDescriptor sampler_desc;
@@ -48,12 +38,6 @@ void BindVertices(Command& cmd,
   cmd.BindVertices(vtx_builder.CreateVertexBuffer(host_buffer));
 }
 
-Matrix MakeAnchorScale(const Point& anchor, Vector2 scale) {
-  return Matrix::MakeTranslation({anchor.x, anchor.y, 0}) *
-         Matrix::MakeScale(scale) *
-         Matrix::MakeTranslation({-anchor.x, -anchor.y, 0});
-}
-
 void SetTileMode(SamplerDescriptor* descriptor,
                  const ContentContext& renderer,
                  Entity::TileMode tile_mode) {
@@ -87,7 +71,6 @@ std::shared_ptr<Texture> MakeDownsampleSubpass(
     const SamplerDescriptor& sampler_descriptor,
     const Quad& uvs,
     const ISize& subpass_size,
-    const Vector2 padding,
     Entity::TileMode tile_mode) {
   ContentContext::SubpassCallback subpass_callback =
       [&](const ContentContext& renderer, RenderPass& pass) {
@@ -104,23 +87,13 @@ std::shared_ptr<Texture> MakeDownsampleSubpass(
         frame_info.texture_sampler_y_coord_scale = 1.0;
         frame_info.alpha = 1.0;
 
-        // Insert transparent gutter around the downsampled image so the blur
-        // creates a halo effect. This compensates for when the expanded clip
-        // region can't give us the full gutter we want.
-        Vector2 texture_size = Vector2(input_texture->GetSize());
-        Quad guttered_uvs =
-            MakeAnchorScale({0.5, 0.5},
-                            (texture_size + padding * 2) / texture_size)
-                .Transform(uvs);
-
-        BindVertices<TextureFillVertexShader>(
-            cmd, host_buffer,
-            {
-                {Point(0, 0), guttered_uvs[0]},
-                {Point(1, 0), guttered_uvs[1]},
-                {Point(0, 1), guttered_uvs[2]},
-                {Point(1, 1), guttered_uvs[3]},
-            });
+        BindVertices<TextureFillVertexShader>(cmd, host_buffer,
+                                              {
+                                                  {Point(0, 0), uvs[0]},
+                                                  {Point(1, 0), uvs[1]},
+                                                  {Point(0, 1), uvs[2]},
+                                                  {Point(1, 1), uvs[3]},
+                                              });
 
         SamplerDescriptor linear_sampler_descriptor = sampler_descriptor;
         SetTileMode(&linear_sampler_descriptor, renderer, tile_mode);
@@ -270,17 +243,17 @@ std::optional<Entity> GaussianBlurFilterContents::RenderFilter(
   Vector2 blur_radius = {CalculateBlurRadius(scaled_sigma.x),
                          CalculateBlurRadius(scaled_sigma.y)};
   Vector2 padding(ceil(blur_radius.x), ceil(blur_radius.y));
+  Vector2 local_padding =
+      (entity.GetTransform().Basis() * effect_transform.Basis() * padding)
+          .Abs();
 
   // Apply as much of the desired padding as possible from the source. This may
   // be ignored so must be accounted for in the downsample pass by adding a
   // transparent gutter.
-  std::optional<Rect> expanded_coverage_hint = ExpandCoverageHint(
-      coverage_hint, entity.GetTransform() * effect_transform, padding);
-  // TODO(gaaclarke): How much of the gutter is thrown away can be used to
-  //                  adjust the padding that is added in the downsample pass.
-  //                  For example, if we get all the padding we requested from
-  //                  the expanded_coverage_hint, there is no need to add a
-  //                  transparent gutter.
+  std::optional<Rect> expanded_coverage_hint;
+  if (coverage_hint.has_value()) {
+    expanded_coverage_hint = coverage_hint->Expand(local_padding);
+  }
 
   std::optional<Snapshot> input_snapshot =
       inputs[0]->GetSnapshot("GaussianBlur", renderer, entity,
@@ -300,21 +273,28 @@ std::optional<Entity> GaussianBlurFilterContents::RenderFilter(
   // gutter from the expanded_coverage_hint, we can skip the downsample pass.
   // pass.
   Vector2 downsample_scalar(desired_scalar, desired_scalar);
-  Vector2 padded_size =
-      Vector2(input_snapshot->texture->GetSize()) + 2.0 * padding;
-  Vector2 downsampled_size = padded_size * downsample_scalar;
-  // TODO(gaaclarke): I don't think we are correctly handling this fractional
-  //                  amount we are throwing away.
+  Rect source_rect = Rect::MakeSize(input_snapshot->texture->GetSize());
+  Rect source_rect_padded = source_rect.Expand(padding);
+  Matrix padding_snapshot_adjustment = Matrix::MakeTranslation(-padding);
+  // TODO(gaaclarke): The padding could be removed if we know it's not needed or
+  //   resized to account for the expanded_clip_coverage. There doesn't appear
+  //   to be the math to make those calculations though. The following
+  //   optimization works, but causes a shimmer as a result of
+  //   https://github.com/flutter/flutter/issues/140193 so it isn't applied.
+  //
+  //   !input_snapshot->GetCoverage()->Expand(-local_padding)
+  //     .Contains(coverage_hint.value()))
+  Vector2 downsampled_size = source_rect_padded.size * downsample_scalar;
   ISize subpass_size =
       ISize(round(downsampled_size.x), round(downsampled_size.y));
-  Vector2 effective_scalar = subpass_size / padded_size;
+  Vector2 effective_scalar = Vector2(subpass_size) / source_rect_padded.size;
 
-  Quad uvs =
-      CalculateUVs(inputs[0], entity, input_snapshot->texture->GetSize());
+  Quad uvs = CalculateUVs(inputs[0], entity, source_rect_padded,
+                          input_snapshot->texture->GetSize());
 
   std::shared_ptr<Texture> pass1_out_texture = MakeDownsampleSubpass(
       renderer, input_snapshot->texture, input_snapshot->sampler_descriptor,
-      uvs, subpass_size, padding, tile_mode_);
+      uvs, subpass_size, tile_mode_);
 
   Vector2 pass1_pixel_size = 1.0 / Vector2(pass1_out_texture->GetSize());
 
@@ -343,13 +323,12 @@ std::optional<Entity> GaussianBlurFilterContents::RenderFilter(
       MinMagFilter::kLinear, SamplerAddressMode::kClampToEdge);
 
   return Entity::FromSnapshot(
-      Snapshot{
-          .texture = pass3_out_texture,
-          .transform = input_snapshot->transform *
-                       Matrix::MakeTranslation({-padding.x, -padding.y, 0}) *
-                       Matrix::MakeScale(1 / effective_scalar),
-          .sampler_descriptor = sampler_desc,
-          .opacity = input_snapshot->opacity},
+      Snapshot{.texture = pass3_out_texture,
+               .transform = input_snapshot->transform *
+                            padding_snapshot_adjustment *
+                            Matrix::MakeScale(1 / effective_scalar),
+               .sampler_descriptor = sampler_desc,
+               .opacity = input_snapshot->opacity},
       entity.GetBlendMode(), entity.GetClipDepth());
 }
 
@@ -360,11 +339,10 @@ Scalar GaussianBlurFilterContents::CalculateBlurRadius(Scalar sigma) {
 Quad GaussianBlurFilterContents::CalculateUVs(
     const std::shared_ptr<FilterInput>& filter_input,
     const Entity& entity,
+    const Rect& source_rect,
     const ISize& texture_size) {
   Matrix input_transform = filter_input->GetLocalTransform(entity);
-  Rect snapshot_rect =
-      Rect::MakeXYWH(0, 0, texture_size.width, texture_size.height);
-  Quad coverage_quad = snapshot_rect.GetTransformedPoints(input_transform);
+  Quad coverage_quad = source_rect.GetTransformedPoints(input_transform);
 
   Matrix uv_transform = Matrix::MakeScale(
       {1.0f / texture_size.width, 1.0f / texture_size.height, 1.0f});

impeller/entity/contents/filters/gaussian_blur_filter_contents.h

@@ -41,10 +41,12 @@ class GaussianBlurFilterContents final : public FilterContents {
   /// Calculate the UV coordinates for rendering the filter_input.
   /// @param filter_input The FilterInput that should be rendered.
   /// @param entity The associated entity for the filter_input.
-  /// @param texture_size The size of the texture_size the uvs will be used for.
+  /// @param source_rect The rect in source coordinates to convert to uvs.
+  /// @param texture_size The rect to convert in source coordinates.
   static Quad CalculateUVs(const std::shared_ptr<FilterInput>& filter_input,
                            const Entity& entity,
-                           const ISize& pass_size);
+                           const Rect& source_rect,
+                           const ISize& texture_size);
 
   /// Calculate the scale factor for the downsample pass given a sigma value.
   ///

impeller/entity/contents/filters/gaussian_blur_filter_contents_unittests.cc

@@ -285,8 +285,8 @@ TEST_P(GaussianBlurFilterContentsTest, CalculateUVsSimple) {
   std::shared_ptr<Texture> texture = MakeTexture(desc);
   auto filter_input = FilterInput::Make(texture);
   Entity entity;
-  Quad uvs = GaussianBlurFilterContents::CalculateUVs(filter_input, entity,
-                                                      ISize(100, 100));
+  Quad uvs = GaussianBlurFilterContents::CalculateUVs(
+      filter_input, entity, Rect::MakeSize(ISize(100, 100)), ISize(100, 100));
   std::optional<Rect> uvs_bounds = Rect::MakePointBounds(uvs);
   EXPECT_TRUE(uvs_bounds.has_value());
   if (uvs_bounds.has_value()) {