Reland: [Impeller] Use downsample shader for blur instead of mip levels. (flutter/engine#54149)

relands https://github.com/flutter/engine/pull/53760
reverted in https://github.com/flutter/engine/pull/54148

The fix for this was found with the help of Jonah.

Part of a series of gaussian blur changes:
1) https://github.com/flutter/engine/pull/54148
1) https://github.com/flutter/engine/pull/54116
1) https://github.com/flutter/engine/pull/54150
1) https://github.com/flutter/engine/pull/54149

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -42203,6 +42203,7 @@ ORIGIN: ../../../flutter/impeller/entity/shaders/rrect_blur.vert + ../../../flut
 ORIGIN: ../../../flutter/impeller/entity/shaders/runtime_effect.vert + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/solid_fill.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/solid_fill.vert + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/entity/shaders/texture_downsample.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/texture_fill.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/texture_fill.vert + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/texture_fill_strict_src.frag + ../../../flutter/LICENSE
@@ -45083,6 +45084,7 @@ FILE: ../../../flutter/impeller/entity/shaders/rrect_blur.vert
 FILE: ../../../flutter/impeller/entity/shaders/runtime_effect.vert
 FILE: ../../../flutter/impeller/entity/shaders/solid_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/solid_fill.vert
+FILE: ../../../flutter/impeller/entity/shaders/texture_downsample.frag
 FILE: ../../../flutter/impeller/entity/shaders/texture_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/texture_fill.vert
 FILE: ../../../flutter/impeller/entity/shaders/texture_fill_strict_src.frag

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

@@ -1041,160 +1041,6 @@ TEST_P(AiksTest, GuassianBlurUpdatesMipmapContents) {
   ASSERT_TRUE(OpenPlaygroundHere(callback));
 }
 
-TEST_P(AiksTest, GaussianBlurSetsMipCountOnPass) {
-  Canvas canvas;
-  canvas.DrawCircle({100, 100}, 50, {.color = Color::CornflowerBlue()});
-  canvas.SaveLayer({}, std::nullopt,
-                   ImageFilter::MakeBlur(Sigma(3), Sigma(3),
-                                         FilterContents::BlurStyle::kNormal,
-                                         Entity::TileMode::kClamp));
-  canvas.Restore();
-
-  Picture picture = canvas.EndRecordingAsPicture();
-  EXPECT_EQ(4, picture.pass->GetRequiredMipCount());
-}
-
-TEST_P(AiksTest, GaussianBlurAllocatesCorrectMipCountRenderTarget) {
-  size_t blur_required_mip_count =
-      GetParam() == PlaygroundBackend::kOpenGLES ? 1 : 4;
-
-  Canvas canvas;
-  canvas.DrawCircle({100, 100}, 50, {.color = Color::CornflowerBlue()});
-  canvas.SaveLayer({}, std::nullopt,
-                   ImageFilter::MakeBlur(Sigma(3), Sigma(3),
-                                         FilterContents::BlurStyle::kNormal,
-                                         Entity::TileMode::kClamp));
-  canvas.Restore();
-
-  Picture picture = canvas.EndRecordingAsPicture();
-  std::shared_ptr<RenderTargetCache> cache =
-      std::make_shared<RenderTargetCache>(GetContext()->GetResourceAllocator());
-  AiksContext aiks_context(GetContext(), nullptr, cache);
-  picture.ToImage(aiks_context, {100, 100});
-
-  size_t max_mip_count = 0;
-  for (auto it = cache->GetRenderTargetDataBegin();
-       it != cache->GetRenderTargetDataEnd(); ++it) {
-    max_mip_count = std::max(it->config.mip_count, max_mip_count);
-  }
-  EXPECT_EQ(max_mip_count, blur_required_mip_count);
-}
-
-TEST_P(AiksTest, GaussianBlurMipMapNestedLayer) {
-  fml::testing::LogCapture log_capture;
-  size_t blur_required_mip_count =
-      GetParam() == PlaygroundBackend::kOpenGLES ? 1 : 4;
-
-  Canvas canvas;
-  canvas.DrawPaint({.color = Color::Wheat()});
-  canvas.SaveLayer({.blend_mode = BlendMode::kMultiply});
-  canvas.DrawCircle({100, 100}, 50, {.color = Color::CornflowerBlue()});
-  canvas.SaveLayer({}, std::nullopt,
-                   ImageFilter::MakeBlur(Sigma(30), Sigma(30),
-                                         FilterContents::BlurStyle::kNormal,
-                                         Entity::TileMode::kClamp));
-  canvas.DrawCircle({200, 200}, 50, {.color = Color::Chartreuse()});
-
-  Picture picture = canvas.EndRecordingAsPicture();
-  std::shared_ptr<RenderTargetCache> cache =
-      std::make_shared<RenderTargetCache>(GetContext()->GetResourceAllocator());
-  AiksContext aiks_context(GetContext(), nullptr, cache);
-  picture.ToImage(aiks_context, {100, 100});
-
-  size_t max_mip_count = 0;
-  for (auto it = cache->GetRenderTargetDataBegin();
-       it != cache->GetRenderTargetDataEnd(); ++it) {
-    max_mip_count = std::max(it->config.mip_count, max_mip_count);
-  }
-  EXPECT_EQ(max_mip_count, blur_required_mip_count);
-  // The log is FML_DLOG, so only check in debug builds.
-#ifndef NDEBUG
-  if (GetParam() != PlaygroundBackend::kOpenGLES) {
-    EXPECT_EQ(log_capture.str().find(GaussianBlurFilterContents::kNoMipsError),
-              std::string::npos);
-  } else {
-    EXPECT_NE(log_capture.str().find(GaussianBlurFilterContents::kNoMipsError),
-              std::string::npos);
-  }
-#endif
-}
-
-TEST_P(AiksTest, GaussianBlurMipMapImageFilter) {
-  size_t blur_required_mip_count =
-      GetParam() == PlaygroundBackend::kOpenGLES ? 1 : 4;
-  fml::testing::LogCapture log_capture;
-  Canvas canvas;
-  canvas.SaveLayer(
-      {.image_filter = ImageFilter::MakeBlur(Sigma(30), Sigma(30),
-                                             FilterContents::BlurStyle::kNormal,
-                                             Entity::TileMode::kClamp)});
-  canvas.DrawCircle({200, 200}, 50, {.color = Color::Chartreuse()});
-
-  Picture picture = canvas.EndRecordingAsPicture();
-  std::shared_ptr<RenderTargetCache> cache =
-      std::make_shared<RenderTargetCache>(GetContext()->GetResourceAllocator());
-  AiksContext aiks_context(GetContext(), nullptr, cache);
-  picture.ToImage(aiks_context, {1024, 768});
-
-  size_t max_mip_count = 0;
-  for (auto it = cache->GetRenderTargetDataBegin();
-       it != cache->GetRenderTargetDataEnd(); ++it) {
-    max_mip_count = std::max(it->config.mip_count, max_mip_count);
-  }
-  EXPECT_EQ(max_mip_count, blur_required_mip_count);
-  // The log is FML_DLOG, so only check in debug builds.
-#ifndef NDEBUG
-  if (GetParam() != PlaygroundBackend::kOpenGLES) {
-    EXPECT_EQ(log_capture.str().find(GaussianBlurFilterContents::kNoMipsError),
-              std::string::npos);
-  } else {
-    EXPECT_NE(log_capture.str().find(GaussianBlurFilterContents::kNoMipsError),
-              std::string::npos);
-  }
-#endif
-}
-
-TEST_P(AiksTest, GaussianBlurMipMapSolidColor) {
-  size_t blur_required_mip_count =
-      GetParam() == PlaygroundBackend::kOpenGLES ? 1 : 4;
-  fml::testing::LogCapture log_capture;
-  Canvas canvas;
-  canvas.DrawPath(PathBuilder{}
-                      .MoveTo({100, 100})
-                      .LineTo({200, 100})
-                      .LineTo({150, 200})
-                      .LineTo({50, 200})
-                      .Close()
-                      .TakePath(),
-                  {.color = Color::Chartreuse(),
-                   .image_filter = ImageFilter::MakeBlur(
-                       Sigma(30), Sigma(30), FilterContents::BlurStyle::kNormal,
-                       Entity::TileMode::kClamp)});
-
-  Picture picture = canvas.EndRecordingAsPicture();
-  std::shared_ptr<RenderTargetCache> cache =
-      std::make_shared<RenderTargetCache>(GetContext()->GetResourceAllocator());
-  AiksContext aiks_context(GetContext(), nullptr, cache);
-  picture.ToImage(aiks_context, {1024, 768});
-
-  size_t max_mip_count = 0;
-  for (auto it = cache->GetRenderTargetDataBegin();
-       it != cache->GetRenderTargetDataEnd(); ++it) {
-    max_mip_count = std::max(it->config.mip_count, max_mip_count);
-  }
-  EXPECT_EQ(max_mip_count, blur_required_mip_count);
-  // The log is FML_DLOG, so only check in debug builds.
-#ifndef NDEBUG
-  if (GetParam() != PlaygroundBackend::kOpenGLES) {
-    EXPECT_EQ(log_capture.str().find(GaussianBlurFilterContents::kNoMipsError),
-              std::string::npos);
-  } else {
-    EXPECT_NE(log_capture.str().find(GaussianBlurFilterContents::kNoMipsError),
-              std::string::npos);
-  }
-#endif
-}
-
 TEST_P(AiksTest, MaskBlurDoesntStretchContents) {
   Scalar sigma = 70;
   auto callback = [&](AiksContext& renderer) -> std::optional<Picture> {

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

@@ -185,37 +185,6 @@ void Canvas::Save(uint32_t total_content_depth) {
   Save(false, total_content_depth);
 }
 
-namespace {
-class MipCountVisitor : public ImageFilterVisitor {
- public:
-  virtual void Visit(const BlurImageFilter& filter) {
-    required_mip_count_ = FilterContents::kBlurFilterRequiredMipCount;
-  }
-  virtual void Visit(const LocalMatrixImageFilter& filter) {
-    required_mip_count_ = 1;
-  }
-  virtual void Visit(const DilateImageFilter& filter) {
-    required_mip_count_ = 1;
-  }
-  virtual void Visit(const ErodeImageFilter& filter) {
-    required_mip_count_ = 1;
-  }
-  virtual void Visit(const MatrixImageFilter& filter) {
-    required_mip_count_ = 1;
-  }
-  virtual void Visit(const ComposeImageFilter& filter) {
-    required_mip_count_ = 1;
-  }
-  virtual void Visit(const ColorImageFilter& filter) {
-    required_mip_count_ = 1;
-  }
-  int32_t GetRequiredMipCount() const { return required_mip_count_; }
-
- private:
-  int32_t required_mip_count_ = -1;
-};
-}  // namespace
-
 void Canvas::Save(bool create_subpass,
                   uint32_t total_content_depth,
                   BlendMode blend_mode,
@@ -240,11 +209,6 @@ void Canvas::Save(bool create_subpass,
             return filter;
           };
       subpass->SetBackdropFilter(backdrop_filter_proc);
-      MipCountVisitor mip_count_visitor;
-      backdrop_filter->Visit(mip_count_visitor);
-      current_pass_->SetRequiredMipCount(
-          std::max(current_pass_->GetRequiredMipCount(),
-                   mip_count_visitor.GetRequiredMipCount()));
     }
     subpass->SetBlendMode(blend_mode);
     current_pass_ = GetCurrentPass().AddSubpass(std::move(subpass));
@@ -873,11 +837,6 @@ void Canvas::SaveLayer(const Paint& paint,
     new_layer_pass.SetBoundsLimit(bounds, bounds_promise);
   }
 
-  if (paint.image_filter) {
-    MipCountVisitor mip_count_visitor;
-    paint.image_filter->Visit(mip_count_visitor);
-    new_layer_pass.SetRequiredMipCount(mip_count_visitor.GetRequiredMipCount());
-  }
   // When applying a save layer, absorb any pending distributed opacity.
   Paint paint_copy = paint;
   paint_copy.color.alpha *= transform_stack_.back().distributed_opacity;

engine/src/flutter/impeller/entity/BUILD.gn

@@ -50,6 +50,7 @@ impeller_shaders("entity_shaders") {
     "shaders/blending/vertices_uber.frag",
     "shaders/gradients/fast_gradient.vert",
     "shaders/gradients/fast_gradient.frag",
+    "shaders/texture_downsample.frag",
   ]
 }
 

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

@@ -428,6 +428,7 @@ ContentContext::ContentContext(
         {static_cast<Scalar>(BlendSelectValues::kSoftLight), supports_decal});
   }
 
+  texture_downsample_pipelines_.CreateDefault(*context_, options_trianglestrip);
   rrect_blur_pipelines_.CreateDefault(*context_, options_trianglestrip);
   texture_strict_src_pipelines_.CreateDefault(*context_, options);
   tiled_texture_pipelines_.CreateDefault(*context_, options, {supports_decal});

engine/src/flutter/impeller/entity/contents/content_context.h

@@ -48,6 +48,7 @@
 #include "impeller/entity/solid_fill.vert.h"
 #include "impeller/entity/srgb_to_linear_filter.frag.h"
 #include "impeller/entity/sweep_gradient_fill.frag.h"
+#include "impeller/entity/texture_downsample.frag.h"
 #include "impeller/entity/texture_fill.frag.h"
 #include "impeller/entity/texture_fill.vert.h"
 #include "impeller/entity/texture_fill_strict_src.frag.h"
@@ -110,6 +111,9 @@ using RRectBlurPipeline =
     RenderPipelineHandle<RrectBlurVertexShader, RrectBlurFragmentShader>;
 using TexturePipeline =
     RenderPipelineHandle<TextureFillVertexShader, TextureFillFragmentShader>;
+using TextureDownsamplePipeline =
+    RenderPipelineHandle<TextureFillVertexShader,
+                         TextureDownsampleFragmentShader>;
 using TextureStrictSrcPipeline =
     RenderPipelineHandle<TextureFillVertexShader,
                          TextureFillStrictSrcFragmentShader>;
@@ -590,6 +594,11 @@ class ContentContext {
     return GetPipeline(blend_softlight_pipelines_, opts);
   }
 
+  std::shared_ptr<Pipeline<PipelineDescriptor>> GetDownsamplePipeline(
+      ContentContextOptions opts) const {
+    return GetPipeline(texture_downsample_pipelines_, opts);
+  }
+
   // Framebuffer Advanced Blends
   std::shared_ptr<Pipeline<PipelineDescriptor>>
   GetFramebufferBlendColorPipeline(ContentContextOptions opts) const {
@@ -881,6 +890,7 @@ class ContentContext {
       sweep_gradient_ssbo_fill_pipelines_;
   mutable Variants<RRectBlurPipeline> rrect_blur_pipelines_;
   mutable Variants<TexturePipeline> texture_pipelines_;
+  mutable Variants<TextureDownsamplePipeline> texture_downsample_pipelines_;
   mutable Variants<TextureStrictSrcPipeline> texture_strict_src_pipelines_;
 #ifdef IMPELLER_ENABLE_OPENGLES
   mutable Variants<TiledTextureExternalPipeline>

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

@@ -9,6 +9,7 @@
 #include "flutter/fml/make_copyable.h"
 #include "impeller/entity/contents/clip_contents.h"
 #include "impeller/entity/contents/content_context.h"
+#include "impeller/entity/texture_downsample.frag.h"
 #include "impeller/entity/texture_fill.frag.h"
 #include "impeller/entity/texture_fill.vert.h"
 #include "impeller/renderer/render_pass.h"
@@ -19,8 +20,6 @@ namespace impeller {
 using GaussianBlurVertexShader = GaussianBlurPipeline::VertexShader;
 using GaussianBlurFragmentShader = GaussianBlurPipeline::FragmentShader;
 
-const int32_t GaussianBlurFilterContents::kBlurFilterRequiredMipCount = 4;
-
 namespace {
 
 constexpr Scalar kMaxSigma = 500.0f;
@@ -131,28 +130,13 @@ std::optional<Snapshot> GetSnapshot(const std::shared_ptr<FilterInput>& input,
                                     const ContentContext& renderer,
                                     const Entity& entity,
                                     const std::optional<Rect>& coverage_hint) {
-  int32_t mip_count = GaussianBlurFilterContents::kBlurFilterRequiredMipCount;
-  if (renderer.GetContext()->GetBackendType() ==
-      Context::BackendType::kOpenGLES) {
-    // TODO(https://github.com/flutter/flutter/issues/141732): Implement mip map
-    // generation on opengles.
-    mip_count = 1;
-  }
-
   std::optional<Snapshot> input_snapshot =
       input->GetSnapshot("GaussianBlur", renderer, entity,
-                         /*coverage_limit=*/coverage_hint,
+                         /*coverage_limit=*/coverage_hint);
-                         /*mip_count=*/mip_count);
   if (!input_snapshot.has_value()) {
     return std::nullopt;
   }
 
-  // In order to avoid shimmering in downsampling step, we should have mips.
-  if (input_snapshot->texture->GetMipCount() <= 1) {
-    FML_DLOG(ERROR) << GaussianBlurFilterContents::kNoMipsError;
-  }
-  FML_DCHECK(!input_snapshot->texture->NeedsMipmapGeneration());
-
   return input_snapshot;
 }
 
@@ -242,6 +226,7 @@ DownsamplePassArgs CalculateDownsamplePassArgs(
   Scalar desired_scalar =
       std::min(GaussianBlurFilterContents::CalculateScale(scaled_sigma.x),
                GaussianBlurFilterContents::CalculateScale(scaled_sigma.y));
+
   // TODO(jonahwilliams): If desired_scalar is 1.0 and we fully acquired the
   // gutter from the expanded_coverage_hint, we can skip the downsample pass.
   // pass.
@@ -344,50 +329,109 @@ fml::StatusOr<RenderTarget> MakeDownsampleSubpass(
     const SamplerDescriptor& sampler_descriptor,
     const DownsamplePassArgs& pass_args,
     Entity::TileMode tile_mode) {
-  ContentContext::SubpassCallback subpass_callback =
+  // If the texture already had mip levels generated, then we can use the
-      [&](const ContentContext& renderer, RenderPass& pass) {
+  // original downsample shader.
-        HostBuffer& host_buffer = renderer.GetTransientsBuffer();
+  if (pass_args.effective_scalar.x >= 0.5f ||
+      (!input_texture->NeedsMipmapGeneration() &&
+       input_texture->GetTextureDescriptor().mip_count > 1)) {
+    ContentContext::SubpassCallback subpass_callback =
+        [&](const ContentContext& renderer, RenderPass& pass) {
+          HostBuffer& host_buffer = renderer.GetTransientsBuffer();
 
-        pass.SetCommandLabel("Gaussian blur downsample");
+          pass.SetCommandLabel("Gaussian blur downsample");
-        auto pipeline_options = OptionsFromPass(pass);
+          auto pipeline_options = OptionsFromPass(pass);
-        pipeline_options.primitive_type = PrimitiveType::kTriangleStrip;
+          pipeline_options.primitive_type = PrimitiveType::kTriangleStrip;
-        pass.SetPipeline(renderer.GetTexturePipeline(pipeline_options));
+          pass.SetPipeline(renderer.GetTexturePipeline(pipeline_options));
 
-        TextureFillVertexShader::FrameInfo frame_info;
+          TextureFillVertexShader::FrameInfo frame_info;
-        frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
+          frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
-        frame_info.texture_sampler_y_coord_scale = 1.0;
+          frame_info.texture_sampler_y_coord_scale = 1.0;
 
-        TextureFillFragmentShader::FragInfo frag_info;
+          TextureFillFragmentShader::FragInfo frag_info;
-        frag_info.alpha = 1.0;
+          frag_info.alpha = 1.0;
 
-        const Quad& uvs = pass_args.uvs;
+          const Quad& uvs = pass_args.uvs;
-        BindVertices<TextureFillVertexShader>(pass, host_buffer,
+          BindVertices<TextureFillVertexShader>(pass, host_buffer,
-                                              {
+                                                {
-                                                  {Point(0, 0), uvs[0]},
+                                                    {Point(0, 0), uvs[0]},
-                                                  {Point(1, 0), uvs[1]},
+                                                    {Point(1, 0), uvs[1]},
-                                                  {Point(0, 1), uvs[2]},
+                                                    {Point(0, 1), uvs[2]},
-                                                  {Point(1, 1), uvs[3]},
+                                                    {Point(1, 1), uvs[3]},
-                                              });
+                                                });
 
-        SamplerDescriptor linear_sampler_descriptor = sampler_descriptor;
+          SamplerDescriptor linear_sampler_descriptor = sampler_descriptor;
-        SetTileMode(&linear_sampler_descriptor, renderer, tile_mode);
+          SetTileMode(&linear_sampler_descriptor, renderer, tile_mode);
-        linear_sampler_descriptor.mag_filter = MinMagFilter::kLinear;
+          linear_sampler_descriptor.mag_filter = MinMagFilter::kLinear;
-        linear_sampler_descriptor.min_filter = MinMagFilter::kLinear;
+          linear_sampler_descriptor.min_filter = MinMagFilter::kLinear;
-        TextureFillVertexShader::BindFrameInfo(
+          TextureFillVertexShader::BindFrameInfo(
-            pass, host_buffer.EmplaceUniform(frame_info));
+              pass, host_buffer.EmplaceUniform(frame_info));
-        TextureFillFragmentShader::BindFragInfo(
+          TextureFillFragmentShader::BindFragInfo(
-            pass, host_buffer.EmplaceUniform(frag_info));
+              pass, host_buffer.EmplaceUniform(frag_info));
-        TextureFillFragmentShader::BindTextureSampler(
+          TextureFillFragmentShader::BindTextureSampler(
-            pass, input_texture,
+              pass, input_texture,
-            renderer.GetContext()->GetSamplerLibrary()->GetSampler(
+              renderer.GetContext()->GetSamplerLibrary()->GetSampler(
-                linear_sampler_descriptor));
+                  linear_sampler_descriptor));
 
-        return pass.Draw().ok();
+          return pass.Draw().ok();
-      };
+        };
-  fml::StatusOr<RenderTarget> render_target =
+    return renderer.MakeSubpass("Gaussian Blur Filter", pass_args.subpass_size,
-      renderer.MakeSubpass("Gaussian Blur Filter", pass_args.subpass_size,
+                                command_buffer, subpass_callback);
-                           command_buffer, subpass_callback);
+  } else {
-  return render_target;
+    // This assumes we don't scale below 1/16.
+    Scalar edge = 1.0;
+    Scalar ratio = 0.25;
+    if (pass_args.effective_scalar.x <= 0.0625f) {
+      edge = 7.0;
+      ratio = 1.0f / 64.0f;
+    } else if (pass_args.effective_scalar.x <= 0.125f) {
+      edge = 3.0;
+      ratio = 1.0f / 16.0f;
+    }
+    ContentContext::SubpassCallback subpass_callback =
+        [&](const ContentContext& renderer, RenderPass& pass) {
+          HostBuffer& host_buffer = renderer.GetTransientsBuffer();
+
+          pass.SetCommandLabel("Gaussian blur downsample");
+          auto pipeline_options = OptionsFromPass(pass);
+          pipeline_options.primitive_type = PrimitiveType::kTriangleStrip;
+          pass.SetPipeline(renderer.GetDownsamplePipeline(pipeline_options));
+
+          TextureFillVertexShader::FrameInfo frame_info;
+          frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
+          frame_info.texture_sampler_y_coord_scale = 1.0;
+
+          TextureDownsampleFragmentShader::FragInfo frag_info;
+          frag_info.edge = edge;
+          frag_info.ratio = ratio;
+          frag_info.pixel_size = Vector2(1.0f / Size(input_texture->GetSize()));
+
+          const Quad& uvs = pass_args.uvs;
+          BindVertices<TextureFillVertexShader>(pass, 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);
+          linear_sampler_descriptor.mag_filter = MinMagFilter::kLinear;
+          linear_sampler_descriptor.min_filter = MinMagFilter::kLinear;
+          TextureFillVertexShader::BindFrameInfo(
+              pass, host_buffer.EmplaceUniform(frame_info));
+          TextureDownsampleFragmentShader::BindFragInfo(
+              pass, host_buffer.EmplaceUniform(frag_info));
+          TextureDownsampleFragmentShader::BindTextureSampler(
+              pass, input_texture,
+              renderer.GetContext()->GetSamplerLibrary()->GetSampler(
+                  linear_sampler_descriptor));
+
+          return pass.Draw().ok();
+        };
+    return renderer.MakeSubpass("Gaussian Blur Filter", pass_args.subpass_size,
+                                command_buffer, subpass_callback);
+  }
 }
 
 fml::StatusOr<RenderTarget> MakeBlurSubpass(
@@ -554,9 +598,6 @@ Entity ApplyBlurStyle(FilterContents::BlurStyle blur_style,
 }
 }  // namespace
 
-std::string_view GaussianBlurFilterContents::kNoMipsError =
-    "Applying gaussian blur without mipmap.";
-
 GaussianBlurFilterContents::GaussianBlurFilterContents(
     Scalar sigma_x,
     Scalar sigma_y,

engine/src/flutter/impeller/entity/contents/filters/gaussian_blur_filter_contents.h

@@ -46,9 +46,6 @@ GaussianBlurPipeline::FragmentShader::KernelSamples LerpHackKernelSamples(
 /// Note: This will replace `DirectionalGaussianBlurFilterContents`.
 class GaussianBlurFilterContents final : public FilterContents {
  public:
-  static std::string_view kNoMipsError;
-  static const int32_t kBlurFilterRequiredMipCount;
-
   explicit GaussianBlurFilterContents(
       Scalar sigma_x,
       Scalar sigma_y,

engine/src/flutter/impeller/entity/shaders/texture_downsample.frag

@@ -0,0 +1,34 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+precision mediump float;
+
+#include <impeller/constants.glsl>
+#include <impeller/types.glsl>
+
+uniform f16sampler2D texture_sampler;
+
+uniform FragInfo {
+  float edge;
+  float ratio;
+  vec2 pixel_size;
+}
+frag_info;
+
+in highp vec2 v_texture_coords;
+
+out vec4 frag_color;
+
+void main() {
+  vec4 total = vec4(0.0);
+  for (float i = -frag_info.edge; i <= frag_info.edge; i += 2) {
+    for (float j = -frag_info.edge; j <= frag_info.edge; j += 2) {
+      total += (texture(texture_sampler,
+                        v_texture_coords + frag_info.pixel_size * vec2(i, j),
+                        float16_t(kDefaultMipBias)) *
+                frag_info.ratio);
+    }
+  }
+  frag_color = total;
+}

engine/src/flutter/impeller/tools/malioc.json

@@ -4729,6 +4729,126 @@
       }
     }
   },
+  "flutter/impeller/entity/gles/texture_downsample.frag.gles": {
+    "Mali-G78": {
+      "core": "Mali-G78",
+      "filename": "flutter/impeller/entity/gles/texture_downsample.frag.gles",
+      "has_side_effects": false,
+      "has_uniform_computation": true,
+      "modifies_coverage": false,
+      "reads_color_buffer": false,
+      "type": "Fragment",
+      "uses_late_zs_test": false,
+      "uses_late_zs_update": false,
+      "variants": {
+        "Main": {
+          "fp16_arithmetic": 80,
+          "has_stack_spilling": false,
+          "performance": {
+            "longest_path_bound_pipelines": [
+              null
+            ],
+            "longest_path_cycles": [
+              null,
+              null,
+              null,
+              null,
+              null,
+              null,
+              null
+            ],
+            "pipelines": [
+              "arith_total",
+              "arith_fma",
+              "arith_cvt",
+              "arith_sfu",
+              "load_store",
+              "varying",
+              "texture"
+            ],
+            "shortest_path_bound_pipelines": [
+              "arith_total",
+              "arith_cvt"
+            ],
+            "shortest_path_cycles": [
+              0.0625,
+              0.0,
+              0.0625,
+              0.0,
+              0.0,
+              0.0,
+              0.0
+            ],
+            "total_bound_pipelines": [
+              "arith_total",
+              "arith_cvt",
+              "varying",
+              "texture"
+            ],
+            "total_cycles": [
+              0.25,
+              0.125,
+              0.25,
+              0.0,
+              0.0,
+              0.25,
+              0.25
+            ]
+          },
+          "stack_spill_bytes": 0,
+          "thread_occupancy": 100,
+          "uniform_registers_used": 6,
+          "work_registers_used": 19
+        }
+      }
+    },
+    "Mali-T880": {
+      "core": "Mali-T880",
+      "filename": "flutter/impeller/entity/gles/texture_downsample.frag.gles",
+      "has_uniform_computation": false,
+      "type": "Fragment",
+      "variants": {
+        "Main": {
+          "has_stack_spilling": false,
+          "performance": {
+            "longest_path_bound_pipelines": [
+              null
+            ],
+            "longest_path_cycles": [
+              null,
+              null,
+              null
+            ],
+            "pipelines": [
+              "arithmetic",
+              "load_store",
+              "texture"
+            ],
+            "shortest_path_bound_pipelines": [
+              "arithmetic",
+              "load_store"
+            ],
+            "shortest_path_cycles": [
+              1.0,
+              1.0,
+              0.0
+            ],
+            "total_bound_pipelines": [
+              "arithmetic"
+            ],
+            "total_cycles": [
+              3.3333332538604736,
+              1.0,
+              1.0
+            ]
+          },
+          "thread_occupancy": 100,
+          "uniform_registers_used": 1,
+          "work_registers_used": 4
+        }
+      }
+    }
+  },
   "flutter/impeller/entity/gles/texture_fill.frag.gles": {
     "Mali-G78": {
       "core": "Mali-G78",
@@ -7322,6 +7442,78 @@
       }
     }
   },
+  "flutter/impeller/entity/texture_downsample.frag.vkspv": {
+    "Mali-G78": {
+      "core": "Mali-G78",
+      "filename": "flutter/impeller/entity/texture_downsample.frag.vkspv",
+      "has_side_effects": false,
+      "has_uniform_computation": true,
+      "modifies_coverage": false,
+      "reads_color_buffer": false,
+      "type": "Fragment",
+      "uses_late_zs_test": false,
+      "uses_late_zs_update": false,
+      "variants": {
+        "Main": {
+          "fp16_arithmetic": 40,
+          "has_stack_spilling": false,
+          "performance": {
+            "longest_path_bound_pipelines": [
+              null
+            ],
+            "longest_path_cycles": [
+              null,
+              null,
+              null,
+              null,
+              null,
+              null,
+              null
+            ],
+            "pipelines": [
+              "arith_total",
+              "arith_fma",
+              "arith_cvt",
+              "arith_sfu",
+              "load_store",
+              "varying",
+              "texture"
+            ],
+            "shortest_path_bound_pipelines": [
+              "arith_total",
+              "arith_cvt"
+            ],
+            "shortest_path_cycles": [
+              0.109375,
+              0.0,
+              0.109375,
+              0.0,
+              0.0,
+              0.0,
+              0.0
+            ],
+            "total_bound_pipelines": [
+              "arith_total",
+              "arith_cvt"
+            ],
+            "total_cycles": [
+              0.328125,
+              0.09375,
+              0.328125,
+              0.0,
+              0.0,
+              0.25,
+              0.25
+            ]
+          },
+          "stack_spill_bytes": 0,
+          "thread_occupancy": 100,
+          "uniform_registers_used": 8,
+          "work_registers_used": 14
+        }
+      }
+    }
+  },
   "flutter/impeller/entity/texture_fill.frag.vkspv": {
     "Mali-G78": {
       "core": "Mali-G78",