[Impeller] remove mip usage for blur downsample, cap at 1/4

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",
   ]
 }
 

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});

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>

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"
@@ -19,7 +20,7 @@ namespace impeller {
 using GaussianBlurVertexShader = GaussianBlurPipeline::VertexShader;
 using GaussianBlurFragmentShader = GaussianBlurPipeline::FragmentShader;
 
-const int32_t GaussianBlurFilterContents::kBlurFilterRequiredMipCount = 4;
+const int32_t GaussianBlurFilterContents::kBlurFilterRequiredMipCount = 1;
 
 namespace {
 
@@ -242,6 +243,11 @@ DownsamplePassArgs CalculateDownsamplePassArgs(
   Scalar desired_scalar =
       std::min(GaussianBlurFilterContents::CalculateScale(scaled_sigma.x),
                GaussianBlurFilterContents::CalculateScale(scaled_sigma.y));
+
+  if (desired_scalar < 0.25) {
+    desired_scalar = 0.25;
+  }
+
   // 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.
@@ -327,50 +333,93 @@ fml::StatusOr<RenderTarget> MakeDownsampleSubpass(
     const SamplerDescriptor& sampler_descriptor,
     const DownsamplePassArgs& pass_args,
     Entity::TileMode tile_mode) {
-  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.GetTexturePipeline(pipeline_options));
-
-        TextureFillVertexShader::FrameInfo frame_info;
-        frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
-        frame_info.texture_sampler_y_coord_scale = 1.0;
-
-        TextureFillFragmentShader::FragInfo frag_info;
-        frag_info.alpha = 1.0;
-
-        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));
-        TextureFillFragmentShader::BindFragInfo(
-            pass, host_buffer.EmplaceUniform(frag_info));
-        TextureFillFragmentShader::BindTextureSampler(
-            pass, input_texture,
-            renderer.GetContext()->GetSamplerLibrary()->GetSampler(
-                linear_sampler_descriptor));
-
-        return pass.Draw().ok();
-      };
-  fml::StatusOr<RenderTarget> render_target =
-      renderer.MakeSubpass("Gaussian Blur Filter", pass_args.subpass_size,
-                           command_buffer, subpass_callback);
-  return render_target;
+  if (pass_args.effective_scalar.x >= 0.5) {
+    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.GetTexturePipeline(pipeline_options));
+
+          TextureFillVertexShader::FrameInfo frame_info;
+          frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
+          frame_info.texture_sampler_y_coord_scale = 1.0;
+
+          TextureFillFragmentShader::FragInfo frag_info;
+          frag_info.alpha = 1.0;
+
+          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));
+          TextureFillFragmentShader::BindFragInfo(
+              pass, host_buffer.EmplaceUniform(frag_info));
+          TextureFillFragmentShader::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);
+  } else {
+    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.pixel_size = Vector2(1.0 / 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(

impeller/entity/shaders/texture_downsample.frag

@@ -0,0 +1,40 @@
+// 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 {
+  vec2 pixel_size;
+}
+frag_info;
+
+in highp vec2 v_texture_coords;
+
+out f16vec4 frag_color;
+
+void main() {
+  f16vec4 lt = texture(texture_sampler, v_texture_coords - frag_info.pixel_size,
+                       float16_t(kDefaultMipBias)) *
+               0.25hf;
+  f16vec4 rt = texture(texture_sampler,
+                       v_texture_coords + vec2(-frag_info.pixel_size.x,
+                                               frag_info.pixel_size.y),
+                       float16_t(kDefaultMipBias)) *
+               0.25hf;
+  f16vec4 lb = texture(texture_sampler,
+                       v_texture_coords + vec2(frag_info.pixel_size.x,
+                                               -frag_info.pixel_size.y),
+                       float16_t(kDefaultMipBias)) *
+               0.25hf;
+  f16vec4 rb = texture(texture_sampler, v_texture_coords + frag_info.pixel_size,
+                       float16_t(kDefaultMipBias)) *
+               0.25hf;
+
+  frag_color = lt + rb + lb + rb;
+}