[Impeller] Specify blend mode on blend filter commands (flutter#42676)

Side quest of flutter#127232.

This is particularly useful for debugging pipeline blend variations of the blend filter, since we otherwise have to look at the raw pipeline blend ops and figure out and piece together what the blend mode must've been.

Author: bdero

impeller/entity/contents/filters/blend_filter_contents.cc

@@ -8,13 +8,15 @@
 #include <memory>
 #include <optional>
 
+#include "impeller/base/strings.h"
 #include "impeller/core/formats.h"
 #include "impeller/entity/contents/anonymous_contents.h"
 #include "impeller/entity/contents/content_context.h"
 #include "impeller/entity/contents/contents.h"
 #include "impeller/entity/contents/filters/inputs/filter_input.h"
 #include "impeller/entity/contents/solid_color_contents.h"
 #include "impeller/entity/entity.h"
+#include "impeller/geometry/color.h"
 #include "impeller/geometry/path_builder.h"
 #include "impeller/renderer/render_pass.h"
 #include "impeller/renderer/sampler_library.h"
@@ -37,6 +39,7 @@ static std::optional<Entity> AdvancedBlend(
     const ContentContext& renderer,
     const Entity& entity,
     const Rect& coverage,
+    BlendMode blend_mode,
     std::optional<Color> foreground_color,
     bool absorb_opacity,
     PipelineProc pipeline_proc,
@@ -114,7 +117,8 @@ static std::optional<Entity> AdvancedBlend(
         std::invoke(pipeline_proc, renderer, options);
 
     Command cmd;
-    cmd.label = "Advanced Blend Filter";
+    cmd.label =
+        SPrintF("Advanced Blend Filter (%s)", BlendModeToString(blend_mode));
     cmd.BindVertices(vtx_buffer);
     cmd.pipeline = std::move(pipeline);
 
@@ -228,7 +232,8 @@ std::optional<Entity> BlendFilterContents::CreateForegroundAdvancedBlend(
     auto vtx_buffer = vtx_builder.CreateVertexBuffer(host_buffer);
 
     Command cmd;
-    cmd.label = "Foreground Advanced Blend Filter";
+    cmd.label = SPrintF("Foreground Advanced Blend Filter (%s)",
+                        BlendModeToString(blend_mode));
     cmd.BindVertices(vtx_buffer);
     cmd.stencil_reference = entity.GetStencilDepth();
     auto options = OptionsFromPass(pass);
@@ -413,7 +418,8 @@ std::optional<Entity> BlendFilterContents::CreateForegroundPorterDuffBlend(
     auto vtx_buffer = vtx_builder.CreateVertexBuffer(host_buffer);
 
     Command cmd;
-    cmd.label = "Foreground PorterDuff Blend Filter";
+    cmd.label = SPrintF("Foreground PorterDuff Blend Filter (%s)",
+                        BlendModeToString(blend_mode));
     cmd.BindVertices(vtx_buffer);
     cmd.stencil_reference = entity.GetStencilDepth();
     auto options = OptionsFromPass(pass);
@@ -475,7 +481,7 @@ static std::optional<Entity> PipelineBlend(
     const ContentContext& renderer,
     const Entity& entity,
     const Rect& coverage,
-    BlendMode pipeline_blend,
+    BlendMode blend_mode,
     std::optional<Color> foreground_color,
     bool absorb_opacity,
     std::optional<Scalar> alpha) {
@@ -493,7 +499,8 @@ static std::optional<Entity> PipelineBlend(
     auto& host_buffer = pass.GetTransientsBuffer();
 
     Command cmd;
-    cmd.label = "Pipeline Blend Filter";
+    cmd.label =
+        SPrintF("Pipeline Blend Filter (%s)", BlendModeToString(blend_mode));
     auto options = OptionsFromPass(pass);
 
     auto add_blend_command = [&](std::optional<Snapshot> input) {
@@ -548,7 +555,7 @@ static std::optional<Entity> PipelineBlend(
     // Write subsequent textures using the selected blend mode.
 
     if (inputs.size() >= 2) {
-      options.blend_mode = pipeline_blend;
+      options.blend_mode = blend_mode;
       cmd.pipeline = renderer.GetBlendPipeline(options);
 
       for (auto texture_i = inputs.begin() + 1; texture_i < inputs.end();
@@ -570,7 +577,7 @@ static std::optional<Entity> PipelineBlend(
       contents->SetColor(foreground_color.value());
 
       Entity foreground_entity;
-      foreground_entity.SetBlendMode(pipeline_blend);
+      foreground_entity.SetBlendMode(blend_mode);
       foreground_entity.SetContents(contents);
       if (!foreground_entity.Render(renderer, pass)) {
         return false;
@@ -598,19 +605,18 @@ static std::optional<Entity> PipelineBlend(
       entity.GetBlendMode(), entity.GetStencilDepth());
 }
 
-#define BLEND_CASE(mode)                                                     \
-  case BlendMode::k##mode:                                                   \
-    advanced_blend_proc_ = [](const FilterInput::Vector& inputs,             \
-                              const ContentContext& renderer,                \
-                              const Entity& entity, const Rect& coverage,    \
-                              std::optional<Color> fg_color,                 \
-                              bool absorb_opacity,                           \
-                              std::optional<Scalar> alpha) {                 \
-      PipelineProc p = &ContentContext::GetBlend##mode##Pipeline;            \
-      return AdvancedBlend<Blend##mode##Pipeline>(inputs, renderer, entity,  \
-                                                  coverage, fg_color,        \
-                                                  absorb_opacity, p, alpha); \
-    };                                                                       \
+#define BLEND_CASE(mode)                                                      \
+  case BlendMode::k##mode:                                                    \
+    advanced_blend_proc_ =                                                    \
+        [](const FilterInput::Vector& inputs, const ContentContext& renderer, \
+           const Entity& entity, const Rect& coverage, BlendMode blend_mode,  \
+           std::optional<Color> fg_color, bool absorb_opacity,                \
+           std::optional<Scalar> alpha) {                                     \
+          PipelineProc p = &ContentContext::GetBlend##mode##Pipeline;         \
+          return AdvancedBlend<Blend##mode##Pipeline>(                        \
+              inputs, renderer, entity, coverage, blend_mode, fg_color,       \
+              absorb_opacity, p, alpha);                                      \
+        };                                                                    \
     break;
 
 void BlendFilterContents::SetBlendMode(BlendMode blend_mode) {
@@ -683,7 +689,7 @@ std::optional<Entity> BlendFilterContents::RenderFilter(
           inputs[0], renderer, entity, coverage, foreground_color_.value(),
           blend_mode_, GetAlpha(), GetAbsorbOpacity());
     }
-    return advanced_blend_proc_(inputs, renderer, entity, coverage,
+    return advanced_blend_proc_(inputs, renderer, entity, coverage, blend_mode_,
                                 foreground_color_, GetAbsorbOpacity(),
                                 GetAlpha());
   }

impeller/entity/contents/filters/blend_filter_contents.h

@@ -16,6 +16,7 @@ class BlendFilterContents : public ColorFilterContents {
                                           const ContentContext& renderer,
                                           const Entity& entity,
                                           const Rect& coverage,
+                                          BlendMode blend_mode,
                                           std::optional<Color> foreground_color,
                                           bool absorb_opacity,
                                           std::optional<Scalar> alpha)>;

impeller/geometry/color.cc

@@ -7,6 +7,7 @@
 #include <algorithm>
 #include <cmath>
 #include <sstream>
+#include <type_traits>
 
 #include "impeller/base/strings.h"
 #include "impeller/geometry/constants.h"
@@ -37,6 +38,16 @@ static constexpr inline bool ValidateBlendModes() {
 static_assert(ValidateBlendModes(),
               "IMPELLER_FOR_EACH_BLEND_MODE must match impeller::BlendMode.");
 
+#define _IMPELLER_BLEND_MODE_NAME_LIST(blend_mode) #blend_mode,
+
+static constexpr const char* kBlendModeNames[] = {
+    IMPELLER_FOR_EACH_BLEND_MODE(_IMPELLER_BLEND_MODE_NAME_LIST)};
+
+const char* BlendModeToString(BlendMode blend_mode) {
+  return kBlendModeNames[static_cast<std::underlying_type_t<BlendMode>>(
+      blend_mode)];
+}
+
 ColorHSB ColorHSB::FromRGB(Color rgb) {
   Scalar R = rgb.red;
   Scalar G = rgb.green;

impeller/geometry/color.h

@@ -54,7 +54,7 @@ enum class YUVColorSpace { kBT601LimitedRange, kBT601FullRange };
 enum class BlendMode {
   // The following blend modes are able to be used as pipeline blend modes or
   // via `BlendFilterContents`.
-  kClear,
+  kClear = 0,
   kSource,
   kDestination,
   kSourceOver,
@@ -91,6 +91,8 @@ enum class BlendMode {
   kLast = kLuminosity,
 };
 
+const char* BlendModeToString(BlendMode blend_mode);
+
 /**
  *  Represents a RGBA color
  */

impeller/geometry/geometry_unittests.cc

@@ -6,9 +6,11 @@
 
 #include <limits>
 #include <sstream>
+#include <type_traits>
 
 #include "flutter/fml/build_config.h"
 #include "flutter/testing/testing.h"
+#include "impeller/geometry/color.h"
 #include "impeller/geometry/constants.h"
 #include "impeller/geometry/gradient.h"
 #include "impeller/geometry/half.h"
@@ -1446,6 +1448,20 @@ TEST(GeometryTest, ColorMakeRGBA8) {
   }
 }
 
+#define _BLEND_MODE_NAME_CHECK(blend_mode) \
+  case BlendMode::k##blend_mode:           \
+    ASSERT_STREQ(result, #blend_mode);     \
+    break;
+
+TEST(GeometryTest, BlendModeToString) {
+  using BlendT = std::underlying_type_t<BlendMode>;
+  for (BlendT i = 0; i <= static_cast<BlendT>(BlendMode::kLast); i++) {
+    auto mode = static_cast<BlendMode>(i);
+    auto result = BlendModeToString(mode);
+    switch (mode) { IMPELLER_FOR_EACH_BLEND_MODE(_BLEND_MODE_NAME_CHECK) }
+  }
+}
+
 TEST(GeometryTest, CanConvertBetweenDegressAndRadians) {
   {
     auto deg = Degrees{90.0};