Add blend filter support for advanced blends (flutter#81)

impeller/entity/BUILD.gn

@@ -14,6 +14,10 @@ impeller_shaders("entity_shaders") {
     "shaders/solid_fill.vert",
     "shaders/solid_stroke.frag",
     "shaders/solid_stroke.vert",
+    "shaders/texture_blend.frag",
+    "shaders/texture_blend.vert",
+    "shaders/texture_blend_screen.frag",
+    "shaders/texture_blend_screen.vert",
     "shaders/texture_fill.frag",
     "shaders/texture_fill.vert",
     "shaders/glyph_atlas.frag",

impeller/entity/contents/content_context.cc

@@ -18,6 +18,10 @@ ContentContext::ContentContext(std::shared_ptr<Context> context)
   gradient_fill_pipelines_[{}] =
       std::make_unique<GradientFillPipeline>(*context_);
   solid_fill_pipelines_[{}] = std::make_unique<SolidFillPipeline>(*context_);
+  texture_blend_pipelines_[{}] =
+      std::make_unique<TextureBlendPipeline>(*context_);
+  texture_blend_screen_pipelines_[{}] =
+      std::make_unique<TextureBlendScreenPipeline>(*context_);
   texture_pipelines_[{}] = std::make_unique<TexturePipeline>(*context_);
   solid_stroke_pipelines_[{}] =
       std::make_unique<SolidStrokePipeline>(*context_);

impeller/entity/contents/content_context.h

@@ -9,6 +9,8 @@
 
 #include "flutter/fml/hash_combine.h"
 #include "flutter/fml/macros.h"
+#include "fml/logging.h"
+#include "impeller/base/validation.h"
 #include "impeller/entity/entity.h"
 #include "impeller/entity/glyph_atlas.frag.h"
 #include "impeller/entity/glyph_atlas.vert.h"
@@ -21,13 +23,21 @@
 #include "impeller/entity/texture_fill.frag.h"
 #include "impeller/entity/texture_fill.vert.h"
 #include "impeller/renderer/formats.h"
+#include "texture_blend.frag.h"
+#include "texture_blend.vert.h"
+#include "texture_blend_screen.frag.h"
+#include "texture_blend_screen.vert.h"
 
 namespace impeller {
 
 using GradientFillPipeline =
     PipelineT<GradientFillVertexShader, GradientFillFragmentShader>;
 using SolidFillPipeline =
     PipelineT<SolidFillVertexShader, SolidFillFragmentShader>;
+using TextureBlendPipeline =
+    PipelineT<TextureBlendVertexShader, TextureBlendFragmentShader>;
+using TextureBlendScreenPipeline =
+    PipelineT<TextureBlendScreenVertexShader, TextureBlendScreenFragmentShader>;
 using TexturePipeline =
     PipelineT<TextureFillVertexShader, TextureFillFragmentShader>;
 using SolidStrokePipeline =
@@ -75,6 +85,16 @@ class ContentContext {
     return GetPipeline(solid_fill_pipelines_, opts);
   }
 
+  std::shared_ptr<Pipeline> GetTextureBlendPipeline(
+      ContentContextOptions opts) const {
+    return GetPipeline(texture_blend_pipelines_, opts);
+  }
+
+  std::shared_ptr<Pipeline> GetTextureBlendScreenPipeline(
+      ContentContextOptions opts) const {
+    return GetPipeline(texture_blend_screen_pipelines_, opts);
+  }
+
   std::shared_ptr<Pipeline> GetTexturePipeline(
       ContentContextOptions opts) const {
     return GetPipeline(texture_pipelines_, opts);
@@ -115,6 +135,8 @@ class ContentContext {
   // map.
   mutable Variants<GradientFillPipeline> gradient_fill_pipelines_;
   mutable Variants<SolidFillPipeline> solid_fill_pipelines_;
+  mutable Variants<TextureBlendPipeline> texture_blend_pipelines_;
+  mutable Variants<TextureBlendScreenPipeline> texture_blend_screen_pipelines_;
   mutable Variants<TexturePipeline> texture_pipelines_;
   mutable Variants<SolidStrokePipeline> solid_stroke_pipelines_;
   mutable Variants<ClipPipeline> clip_pipelines_;
@@ -123,12 +145,24 @@ class ContentContext {
 
   static void ApplyOptionsToDescriptor(PipelineDescriptor& desc,
                                        const ContentContextOptions& options) {
+    auto blend_mode = options.blend_mode;
+    if (blend_mode > Entity::BlendMode::kLastPipelineBlendMode) {
+      VALIDATION_LOG << "Cannot use blend mode "
+                     << static_cast<int>(options.blend_mode)
+                     << " as a pipeline blend.";
+      blend_mode = Entity::BlendMode::kSourceOver;
+    }
+
     desc.SetSampleCount(options.sample_count);
 
     ColorAttachmentDescriptor color0 = *desc.GetColorAttachmentDescriptor(0u);
     color0.alpha_blend_op = BlendOperation::kAdd;
     color0.color_blend_op = BlendOperation::kAdd;
-    switch (options.blend_mode) {
+
+    static_assert(Entity::BlendMode::kLastPipelineBlendMode ==
+                  Entity::BlendMode::kModulate);
+
+    switch (blend_mode) {
       case Entity::BlendMode::kClear:
         color0.dst_alpha_blend_factor = BlendFactor::kZero;
         color0.dst_color_blend_factor = BlendFactor::kZero;
@@ -214,6 +248,8 @@ class ContentContext {
         color0.src_alpha_blend_factor = BlendFactor::kZero;
         color0.src_color_blend_factor = BlendFactor::kZero;
         break;
+      default:
+        FML_UNREACHABLE();
     }
     desc.SetColorAttachmentDescriptor(0u, std::move(color0));
   }

impeller/entity/contents/filter_contents.cc

@@ -28,10 +28,33 @@ namespace impeller {
 std::shared_ptr<FilterContents> FilterContents::MakeBlend(
     Entity::BlendMode blend_mode,
     InputTextures input_textures) {
-  auto blend = std::make_shared<BlendFilterContents>();
-  blend->SetInputTextures(input_textures);
-  blend->SetBlendMode(blend_mode);
-  return blend;
+  if (blend_mode > Entity::BlendMode::kLastAdvancedBlendMode) {
+    VALIDATION_LOG << "Invalid blend mode " << static_cast<int>(blend_mode)
+                   << " passed to FilterContents::MakeBlend.";
+    return nullptr;
+  }
+
+  if (input_textures.size() < 2 ||
+      blend_mode <= Entity::BlendMode::kLastPipelineBlendMode) {
+    auto blend = std::make_shared<BlendFilterContents>();
+    blend->SetInputTextures(input_textures);
+    blend->SetBlendMode(blend_mode);
+    return blend;
+  }
+
+  if (blend_mode <= Entity::BlendMode::kLastAdvancedBlendMode) {
+    InputVariant blend = input_textures[0];
+    for (auto in_i = input_textures.begin() + 1; in_i < input_textures.end();
+         in_i++) {
+      auto new_blend = std::make_shared<BlendFilterContents>();
+      new_blend->SetInputTextures({blend, *in_i});
+      new_blend->SetBlendMode(blend_mode);
+      blend = new_blend;
+    }
+    return std::get<std::shared_ptr<FilterContents>>(blend);
+  }
+
+  FML_UNREACHABLE();
 }
 
 FilterContents::FilterContents() = default;
@@ -150,20 +173,106 @@ ISize FilterContents::GetOutputSize() const {
  ******* BlendFilterContents
  ******************************************************************************/
 
-BlendFilterContents::BlendFilterContents() = default;
+BlendFilterContents::BlendFilterContents() {
+  SetBlendMode(Entity::BlendMode::kSourceOver);
+}
 
 BlendFilterContents::~BlendFilterContents() = default;
 
+using PipelineProc =
+    std::shared_ptr<Pipeline> (ContentContext::*)(ContentContextOptions) const;
+
+template <typename VS, typename FS>
+static void AdvancedBlendPass(std::shared_ptr<Texture> input_d,
+                              std::shared_ptr<Texture> input_s,
+                              std::shared_ptr<const Sampler> sampler,
+                              const ContentContext& renderer,
+                              RenderPass& pass,
+                              Command& cmd) {}
+
+template <typename VS, typename FS>
+static bool AdvancedBlend(
+    const std::vector<std::shared_ptr<Texture>>& input_textures,
+    const ContentContext& renderer,
+    RenderPass& pass,
+    PipelineProc pipeline_proc) {
+  if (input_textures.size() < 2) {
+    return false;
+  }
+
+  auto& host_buffer = pass.GetTransientsBuffer();
+
+  VertexBufferBuilder<typename VS::PerVertexData> vtx_builder;
+  vtx_builder.AddVertices({
+      {Point(0, 0), Point(0, 0)},
+      {Point(1, 0), Point(1, 0)},
+      {Point(1, 1), Point(1, 1)},
+      {Point(0, 0), Point(0, 0)},
+      {Point(1, 1), Point(1, 1)},
+      {Point(0, 1), Point(0, 1)},
+  });
+  auto vtx_buffer = vtx_builder.CreateVertexBuffer(host_buffer);
+
+  typename VS::FrameInfo frame_info;
+  frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
+
+  auto uniform_view = host_buffer.EmplaceUniform(frame_info);
+  auto sampler = renderer.GetContext()->GetSamplerLibrary()->GetSampler({});
+
+  auto options = OptionsFromPass(pass);
+  options.blend_mode = Entity::BlendMode::kSource;
+  std::shared_ptr<Pipeline> pipeline =
+      std::invoke(pipeline_proc, renderer, options);
+
+  Command cmd;
+  cmd.label = "Advanced Blend Filter";
+  cmd.BindVertices(vtx_buffer);
+  cmd.pipeline = std::move(pipeline);
+  VS::BindFrameInfo(cmd, uniform_view);
+
+  FS::BindTextureSamplerDst(cmd, input_textures[0], sampler);
+  FS::BindTextureSamplerSrc(cmd, input_textures[1], sampler);
+  pass.AddCommand(cmd);
+
+  return true;
+}
+
 void BlendFilterContents::SetBlendMode(Entity::BlendMode blend_mode) {
+  if (blend_mode > Entity::BlendMode::kLastAdvancedBlendMode) {
+    VALIDATION_LOG << "Invalid blend mode " << static_cast<int>(blend_mode)
+                   << " assigned to BlendFilterContents.";
+  }
+
   blend_mode_ = blend_mode;
+
+  if (blend_mode > Entity::BlendMode::kLastPipelineBlendMode) {
+    static_assert(Entity::BlendMode::kLastAdvancedBlendMode ==
+                  Entity::BlendMode::kScreen);
+
+    switch (blend_mode) {
+      case Entity::BlendMode::kScreen:
+        advanced_blend_proc_ =
+            [](const std::vector<std::shared_ptr<Texture>>& input_textures,
+               const ContentContext& renderer, RenderPass& pass) {
+              PipelineProc p = &ContentContext::GetTextureBlendScreenPipeline;
+              return AdvancedBlend<TextureBlendScreenPipeline::VertexShader,
+                                   TextureBlendScreenPipeline::FragmentShader>(
+                  input_textures, renderer, pass, p);
+            };
+        break;
+      default:
+        FML_UNREACHABLE();
+    }
+  }
 }
 
-bool BlendFilterContents::RenderFilter(
+static bool BasicBlend(
     const std::vector<std::shared_ptr<Texture>>& input_textures,
     const ContentContext& renderer,
-    RenderPass& pass) const {
-  using VS = TexturePipeline::VertexShader;
-  using FS = TexturePipeline::FragmentShader;
+    RenderPass& pass,
+    Entity::BlendMode basic_blend) {
+  using VS = TextureBlendPipeline::VertexShader;
+  using FS = TextureBlendPipeline::FragmentShader;
 
   auto& host_buffer = pass.GetTransientsBuffer();
 
@@ -180,24 +289,63 @@ bool BlendFilterContents::RenderFilter(
 
   VS::FrameInfo frame_info;
   frame_info.mvp = Matrix::MakeOrthographic(ISize(1, 1));
-  frame_info.alpha = 1;
 
   auto uniform_view = host_buffer.EmplaceUniform(frame_info);
   auto sampler = renderer.GetContext()->GetSamplerLibrary()->GetSampler({});
 
+  // Draw the first texture using kSource.
+
   Command cmd;
-  cmd.label = "Blend Filter";
-  auto options = OptionsFromPass(pass);
-  options.blend_mode = blend_mode_;
-  cmd.pipeline = renderer.GetTexturePipeline(options);
+  cmd.label = "Basic Blend Filter";
   cmd.BindVertices(vtx_buffer);
+  auto options = OptionsFromPass(pass);
+  options.blend_mode = Entity::BlendMode::kSource;
+  cmd.pipeline = renderer.GetTextureBlendPipeline(options);
+  FS::BindTextureSamplerSrc(cmd, input_textures[0], sampler);
   VS::BindFrameInfo(cmd, uniform_view);
-  for (const auto& texture : input_textures) {
-    FS::BindTextureSampler(cmd, texture, sampler);
+  pass.AddCommand(cmd);
+
+  if (input_textures.size() < 2) {
+    return true;
+  }
+
+  // Write subsequent textures using the selected blend mode.
+
+  options.blend_mode = basic_blend;
+  cmd.pipeline = renderer.GetTextureBlendPipeline(options);
+
+  for (auto texture_i = input_textures.begin() + 1;
+       texture_i < input_textures.end(); texture_i++) {
+    FS::BindTextureSamplerSrc(cmd, *texture_i, sampler);
     pass.AddCommand(cmd);
   }
 
   return true;
 }
 
+bool BlendFilterContents::RenderFilter(
+    const std::vector<std::shared_ptr<Texture>>& input_textures,
+    const ContentContext& renderer,
+    RenderPass& pass) const {
+  if (input_textures.empty()) {
+    return true;
+  }
+
+  if (input_textures.size() == 1) {
+    // Nothing to blend.
+    return BasicBlend(input_textures, renderer, pass,
+                      Entity::BlendMode::kSource);
+  }
+
+  if (blend_mode_ <= Entity::BlendMode::kLastPipelineBlendMode) {
+    return BasicBlend(input_textures, renderer, pass, blend_mode_);
+  }
+
+  if (blend_mode_ <= Entity::BlendMode::kLastAdvancedBlendMode) {
+    return advanced_blend_proc_(input_textures, renderer, pass);
+  }
+
+  FML_UNREACHABLE();
+}
+
 }  // namespace impeller

impeller/entity/contents/filter_contents.h

@@ -14,6 +14,8 @@
 
 namespace impeller {
 
+class Pipeline;
+
 /*******************************************************************************
  ******* FilterContents
  ******************************************************************************/
@@ -75,6 +77,11 @@ class FilterContents : public Contents {
 
 class BlendFilterContents : public FilterContents {
  public:
+  using AdvancedBlendProc = std::function<bool(
+      const std::vector<std::shared_ptr<Texture>>& input_textures,
+      const ContentContext& renderer,
+      RenderPass& pass)>;
+
   BlendFilterContents();
 
   ~BlendFilterContents() override;
@@ -86,7 +93,8 @@ class BlendFilterContents : public FilterContents {
                     const ContentContext& renderer,
                     RenderPass& pass) const override;
 
-  Entity::BlendMode blend_mode_ = Entity::BlendMode::kSourceOver;
+  Entity::BlendMode blend_mode_;
+  AdvancedBlendProc advanced_blend_proc_;
 
   FML_DISALLOW_COPY_AND_ASSIGN(BlendFilterContents);
 };