[Impeller] remove varying interpolation for solid colors. (#53281)

This was an early attempt to support batching that ended up not being important, as well as an attempted work around for high memory reads that ended being unrelated (it was blending)

Since its not a performance improvement and just makes things more complicated, remove the feature.

Author: Jonah Williams

impeller/compiler/shader_lib/impeller/types.glsl

@@ -9,12 +9,6 @@
 #extension GL_AMD_gpu_shader_half_float_fetch : enable
 #extension GL_EXT_shader_explicit_arithmetic_types_float16 : enable
 
-#ifdef IMPELLER_TARGET_OPENGLES
-#define IMPELLER_MAYBE_FLAT
-#else
-#define IMPELLER_MAYBE_FLAT flat
-#endif
-
 #ifndef IMPELLER_TARGET_METAL_IOS
 
 precision mediump sampler2D;

impeller/entity/contents/solid_color_contents.cc

@@ -49,9 +49,12 @@ bool SolidColorContents::Render(const ContentContext& renderer,
                                 const Entity& entity,
                                 RenderPass& pass) const {
   using VS = SolidFillPipeline::VertexShader;
+  using FS = SolidFillPipeline::FragmentShader;
+  auto& host_buffer = renderer.GetTransientsBuffer();
 
   VS::FrameInfo frame_info;
-  frame_info.color =
+  FS::FragInfo frag_info;
+  frag_info.color =
       GetColor().Premultiply() * GetGeometry()->ComputeAlphaCoverage(entity);
 
   PipelineBuilderCallback pipeline_callback =
@@ -60,7 +63,8 @@ bool SolidColorContents::Render(const ContentContext& renderer,
       };
   return ColorSourceContents::DrawGeometry<VS>(
       renderer, entity, pass, pipeline_callback, frame_info,
-      [](RenderPass& pass) {
+      [&frag_info, &host_buffer](RenderPass& pass) {
+        FS::BindFragInfo(pass, host_buffer.EmplaceUniform(frag_info));
         pass.SetCommandLabel("Solid Fill");
         return true;
       });

impeller/entity/entity_unittests.cc

@@ -923,6 +923,7 @@ TEST_P(EntityTest, BlendingModeOptions) {
     auto draw_rect = [&context, &pass, &world_matrix](
                          Rect rect, Color color, BlendMode blend_mode) -> bool {
       using VS = SolidFillPipeline::VertexShader;
+      using FS = SolidFillPipeline::FragmentShader;
 
       VertexBufferBuilder<VS::PerVertexData> vtx_builder;
       {
@@ -947,10 +948,12 @@ TEST_P(EntityTest, BlendingModeOptions) {
 
       VS::FrameInfo frame_info;
       frame_info.mvp = pass.GetOrthographicTransform() * world_matrix;
-      frame_info.color = color.Premultiply();
       VS::BindFrameInfo(
           pass, context.GetTransientsBuffer().EmplaceUniform(frame_info));
-
+      FS::FragInfo frag_info;
+      frag_info.color = color.Premultiply();
+      FS::BindFragInfo(
+          pass, context.GetTransientsBuffer().EmplaceUniform(frame_info));
       return pass.Draw().ok();
     };
 

impeller/entity/shaders/solid_fill.frag

@@ -6,10 +6,13 @@ precision mediump float;
 
 #include <impeller/types.glsl>
 
-IMPELLER_MAYBE_FLAT in f16vec4 v_color;
+uniform FragInfo {
+  vec4 color;
+}
+frag_info;
 
-out f16vec4 frag_color;
+out vec4 frag_color;
 
 void main() {
-  frag_color = v_color;
+  frag_color = frag_info.color;
 }

impeller/entity/shaders/solid_fill.vert

@@ -6,15 +6,11 @@
 
 uniform FrameInfo {
   mat4 mvp;
-  f16vec4 color;
 }
 frame_info;
 
 in vec2 position;
 
-IMPELLER_MAYBE_FLAT out mediump f16vec4 v_color;
-
 void main() {
-  v_color = frame_info.color;
   gl_Position = frame_info.mvp * vec4(position, 0.0, 1.0);
 }

impeller/renderer/shader_stage_compatibility_checker.h

@@ -5,6 +5,10 @@
 #ifndef FLUTTER_IMPELLER_RENDERER_SHADER_STAGE_COMPATIBILITY_CHECKER_H_
 #define FLUTTER_IMPELLER_RENDERER_SHADER_STAGE_COMPATIBILITY_CHECKER_H_
 
+#include <cstddef>
+
+#include "impeller/core/shader_types.h"
+
 namespace impeller {
 /// This is a classed use to check that the input slots of fragment shaders
 /// match the output slots of the vertex shaders.
@@ -58,11 +62,17 @@ class ShaderStageCompatibilityChecker {
 // TODO(https://github.com/flutter/flutter/issues/146852): Make impellerc emit
 // an empty array for output slots.
 struct ClipVertexShader;
+struct SolidFillVertexShader;
 
 template <typename FragmentShaderT>
 class ShaderStageCompatibilityChecker<ClipVertexShader, FragmentShaderT> {
  public:
   static constexpr bool Check() { return true; }
 };
+template <typename FragmentShaderT>
+class ShaderStageCompatibilityChecker<SolidFillVertexShader, FragmentShaderT> {
+ public:
+  static constexpr bool Check() { return true; }
+};
 }  // namespace impeller
 #endif  // FLUTTER_IMPELLER_RENDERER_SHADER_STAGE_COMPATIBILITY_CHECKER_H_