[Impeller] Use separate atlases and shaders for color and alpha (#41780)

Creates a separate atlas context and cache for color and alpha bitmap glyphs. Removes SDF shader and uses separate shader for full color glyphs.

Requires #41754

Fixes flutter/flutter#116818
Fixes flutter/flutter#126101

This also fixes #39383 but for light text on a dark background. This problem crops up when we switch to a full color atlas. In this context, the chosen glyph color is important. But with the alpha channel only atlas, its irrelevant.

See diff:

![image](https://user-images.githubusercontent.com/8975114/236598809-f4434764-cd16-4489-9644-4e9a370de7ee.png)

Example app:

```dart
// Copyright 2014 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.

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';

void main() =>
  runApp(
    Container(
      alignment: Alignment.center,
     child: Text(
      '''
 (Unicode Conference)� ا�ذ� س�ع�د �� 10-12 آذار 1997 ب�د��ة ��ا����ت�س� أ��ا��ا. � س�ج�ع ا��ؤت�ر ب�� خبراء �� �ا�ة �طاعات ا�ص�اعة ع�� ا�شب�ة ا�عا���ة ا�تر��ت �������د� ح�ث ستت�� ع�� ا�صع�د�� ا�د��� �ا��ح�� ع�� حد س�اء ��ا�شة سب� استخدا� �����د �� ا��ظ� ا��ائ�ة ����ا �خص ا�تطب��ات ا�حاس�ب�ة� ا�خط�ط� تص��� ا��ص�ص �ا�ح�سبة �تعددة ا��غات.

������������� � � � �''',
textDirection: TextDirection.rtl, style: TextStyle(fontSize: 24, color: Colors.white),
     ),
    ),
  );

```

Author: Jonah Williams

ci/licenses_golden/licenses_flutter

@@ -1297,8 +1297,7 @@ ORIGIN: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_noa
 ORIGIN: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_noalpha_nodecal.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/glyph_atlas.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/glyph_atlas.vert + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/impeller/entity/shaders/glyph_atlas_sdf.frag + ../../../flutter/LICENSE
-ORIGIN: ../../../flutter/impeller/entity/shaders/glyph_atlas_sdf.vert + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/impeller/entity/shaders/glyph_atlas_color.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/gradient_fill.vert + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/linear_gradient_fill.frag + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/impeller/entity/shaders/linear_gradient_ssbo_fill.frag + ../../../flutter/LICENSE
@@ -3910,8 +3909,7 @@ FILE: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_noalp
 FILE: ../../../flutter/impeller/entity/shaders/gaussian_blur/gaussian_blur_noalpha_nodecal.frag
 FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas.frag
 FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas.vert
-FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas_sdf.frag
-FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas_sdf.vert
+FILE: ../../../flutter/impeller/entity/shaders/glyph_atlas_color.frag
 FILE: ../../../flutter/impeller/entity/shaders/gradient_fill.vert
 FILE: ../../../flutter/impeller/entity/shaders/linear_gradient_fill.frag
 FILE: ../../../flutter/impeller/entity/shaders/linear_gradient_ssbo_fill.frag

impeller/entity/BUILD.gn

@@ -43,9 +43,8 @@ impeller_shaders("entity_shaders") {
     "shaders/gaussian_blur/gaussian_blur_noalpha_decal.frag",
     "shaders/gaussian_blur/gaussian_blur_noalpha_nodecal.frag",
     "shaders/glyph_atlas.frag",
+    "shaders/glyph_atlas_color.frag",
     "shaders/glyph_atlas.vert",
-    "shaders/glyph_atlas_sdf.frag",
-    "shaders/glyph_atlas_sdf.vert",
     "shaders/gradient_fill.vert",
     "shaders/linear_to_srgb_filter.frag",
     "shaders/linear_to_srgb_filter.vert",

impeller/entity/contents/content_context.cc

@@ -164,7 +164,8 @@ static std::unique_ptr<PipelineT> CreateDefaultPipeline(
 ContentContext::ContentContext(std::shared_ptr<Context> context)
     : context_(std::move(context)),
       tessellator_(std::make_shared<Tessellator>()),
-      glyph_atlas_context_(std::make_shared<GlyphAtlasContext>()),
+      alpha_glyph_atlas_context_(std::make_shared<GlyphAtlasContext>()),
+      color_glyph_atlas_context_(std::make_shared<GlyphAtlasContext>()),
       scene_context_(std::make_shared<scene::SceneContext>(context_)) {
   if (!context_ || !context_->IsValid()) {
     return;
@@ -286,6 +287,8 @@ ContentContext::ContentContext(std::shared_ptr<Context> context)
       CreateDefaultPipeline<SrgbToLinearFilterPipeline>(*context_);
   glyph_atlas_pipelines_[{}] =
       CreateDefaultPipeline<GlyphAtlasPipeline>(*context_);
+  glyph_atlas_color_pipelines_[{}] =
+      CreateDefaultPipeline<GlyphAtlasColorPipeline>(*context_);
   geometry_color_pipelines_[{}] =
       CreateDefaultPipeline<GeometryColorPipeline>(*context_);
   yuv_to_rgb_filter_pipelines_[{}] =
@@ -378,9 +381,10 @@ std::shared_ptr<Tessellator> ContentContext::GetTessellator() const {
   return tessellator_;
 }
 
-std::shared_ptr<GlyphAtlasContext> ContentContext::GetGlyphAtlasContext()
-    const {
-  return glyph_atlas_context_;
+std::shared_ptr<GlyphAtlasContext> ContentContext::GetGlyphAtlasContext(
+    GlyphAtlas::Type type) const {
+  return type == GlyphAtlas::Type::kAlphaBitmap ? alpha_glyph_atlas_context_
+                                                : color_glyph_atlas_context_;
 }
 
 std::shared_ptr<Context> ContentContext::GetContext() const {

impeller/entity/contents/content_context.h

@@ -32,6 +32,7 @@
 #include "impeller/entity/conical_gradient_fill.frag.h"
 #include "impeller/entity/glyph_atlas.frag.h"
 #include "impeller/entity/glyph_atlas.vert.h"
+#include "impeller/entity/glyph_atlas_color.frag.h"
 #include "impeller/entity/gradient_fill.vert.h"
 #include "impeller/entity/linear_gradient_fill.frag.h"
 #include "impeller/entity/linear_to_srgb_filter.frag.h"
@@ -171,6 +172,8 @@ using SrgbToLinearFilterPipeline =
                     SrgbToLinearFilterFragmentShader>;
 using GlyphAtlasPipeline =
     RenderPipelineT<GlyphAtlasVertexShader, GlyphAtlasFragmentShader>;
+using GlyphAtlasColorPipeline =
+    RenderPipelineT<GlyphAtlasVertexShader, GlyphAtlasColorFragmentShader>;
 using PorterDuffBlendPipeline =
     RenderPipelineT<BlendVertexShader, PorterDuffBlendFragmentShader>;
 // Instead of requiring new shaders for clips, the solid fill stages are used
@@ -469,6 +472,11 @@ class ContentContext {
     return GetPipeline(glyph_atlas_pipelines_, opts);
   }
 
+  std::shared_ptr<Pipeline<PipelineDescriptor>> GetGlyphAtlasColorPipeline(
+      ContentContextOptions opts) const {
+    return GetPipeline(glyph_atlas_color_pipelines_, opts);
+  }
+
   std::shared_ptr<Pipeline<PipelineDescriptor>> GetGeometryColorPipeline(
       ContentContextOptions opts) const {
     return GetPipeline(geometry_color_pipelines_, opts);
@@ -654,7 +662,8 @@ class ContentContext {
 
   std::shared_ptr<Context> GetContext() const;
 
-  std::shared_ptr<GlyphAtlasContext> GetGlyphAtlasContext() const;
+  std::shared_ptr<GlyphAtlasContext> GetGlyphAtlasContext(
+      GlyphAtlas::Type type) const;
 
   const Capabilities& GetDeviceCapabilities() const;
 
@@ -722,6 +731,7 @@ class ContentContext {
   mutable Variants<SrgbToLinearFilterPipeline> srgb_to_linear_filter_pipelines_;
   mutable Variants<ClipPipeline> clip_pipelines_;
   mutable Variants<GlyphAtlasPipeline> glyph_atlas_pipelines_;
+  mutable Variants<GlyphAtlasColorPipeline> glyph_atlas_color_pipelines_;
   mutable Variants<GeometryColorPipeline> geometry_color_pipelines_;
   mutable Variants<YUVToRGBFilterPipeline> yuv_to_rgb_filter_pipelines_;
   mutable Variants<PorterDuffBlendPipeline> porter_duff_blend_pipelines_;
@@ -813,7 +823,8 @@ class ContentContext {
 
   bool is_valid_ = false;
   std::shared_ptr<Tessellator> tessellator_;
-  std::shared_ptr<GlyphAtlasContext> glyph_atlas_context_;
+  std::shared_ptr<GlyphAtlasContext> alpha_glyph_atlas_context_;
+  std::shared_ptr<GlyphAtlasContext> color_glyph_atlas_context_;
   std::shared_ptr<scene::SceneContext> scene_context_;
   bool wireframe_ = false;
 

impeller/entity/contents/text_contents.cc

@@ -112,7 +112,6 @@ static bool CommonRender(
   frag_info.text_color = ToVector(color.Premultiply());
   FS::BindFragInfo(cmd, pass.GetTransientsBuffer().EmplaceUniform(frag_info));
 
-  // Common fragment uniforms for all glyphs.
   FS::BindGlyphAtlasSampler(
       cmd,                  // command
       atlas->GetTexture(),  // texture
@@ -198,9 +197,6 @@ static bool CommonRender(
                                  point * glyph_position.glyph.bounds.size);
         }
         vtx.uv = uv_origin + point * uv_size;
-        vtx.has_color =
-            glyph_position.glyph.type == Glyph::Type::kBitmap ? 1.0 : 0.0;
-
         vertex_builder.AppendVertex(vtx);
       }
     }
@@ -224,16 +220,9 @@ bool TextContents::Render(const ContentContext& renderer,
     return true;
   }
 
-  // This TextContents may be for a frame that doesn't have color, but the
-  // lazy atlas for this scene already does have color.
-  // Benchmarks currently show that creating two atlases per pass regresses
-  // render time. This should get re-evaluated if we start caching atlases
-  // between frames or get significantly faster at creating atlases, because
-  // we're potentially trading memory for time here.
-  auto atlas =
-      ResolveAtlas(lazy_atlas_->HasColor() ? GlyphAtlas::Type::kColorBitmap
-                                           : GlyphAtlas::Type::kAlphaBitmap,
-                   renderer.GetGlyphAtlasContext(), renderer.GetContext());
+  auto type = frame_.GetAtlasType();
+  auto atlas = ResolveAtlas(type, renderer.GetGlyphAtlasContext(type),
+                            renderer.GetContext());
 
   if (!atlas || !atlas->IsValid()) {
     VALIDATION_LOG << "Cannot render glyphs without prepared atlas.";
@@ -245,7 +234,11 @@ bool TextContents::Render(const ContentContext& renderer,
   cmd.label = "TextFrame";
   auto opts = OptionsFromPassAndEntity(pass, entity);
   opts.primitive_type = PrimitiveType::kTriangle;
-  cmd.pipeline = renderer.GetGlyphAtlasPipeline(opts);
+  if (type == GlyphAtlas::Type::kAlphaBitmap) {
+    cmd.pipeline = renderer.GetGlyphAtlasPipeline(opts);
+  } else {
+    cmd.pipeline = renderer.GetGlyphAtlasColorPipeline(opts);
+  }
   cmd.stencil_reference = entity.GetStencilDepth();
 
   return CommonRender(renderer, entity, pass, color, frame_, offset_, atlas,

impeller/entity/shaders/glyph_atlas.frag

@@ -4,23 +4,18 @@
 
 #include <impeller/types.glsl>
 
-uniform sampler2D glyph_atlas_sampler;
+uniform f16sampler2D glyph_atlas_sampler;
 
 uniform FragInfo {
-  vec4 text_color;
+  f16vec4 text_color;
 }
 frag_info;
 
 in vec2 v_uv;
-in float v_has_color;
 
-out vec4 frag_color;
+out f16vec4 frag_color;
 
 void main() {
-  vec4 value = texture(glyph_atlas_sampler, v_uv);
-  if (v_has_color != 1.0) {
-    frag_color = value.aaaa * frag_info.text_color;
-  } else {
-    frag_color = value * frag_info.text_color.a;
-  }
+  f16vec4 value = texture(glyph_atlas_sampler, v_uv);
+  frag_color = value.aaaa * frag_info.text_color;
 }

impeller/entity/shaders/glyph_atlas.vert

@@ -10,15 +10,12 @@ uniform FrameInfo {
 }
 frame_info;
 
-in vec4 position;
+in highp vec4 position;
 in vec2 uv;
-in float has_color;
 
 out vec2 v_uv;
-out float v_has_color;
 
 void main() {
   gl_Position = frame_info.mvp * position;
   v_uv = uv;
-  v_has_color = has_color;
 }

impeller/entity/shaders/glyph_atlas_color.frag

@@ -0,0 +1,21 @@
+// 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.
+
+#include <impeller/types.glsl>
+
+uniform f16sampler2D glyph_atlas_sampler;
+
+uniform FragInfo {
+  f16vec4 text_color;
+}
+frag_info;
+
+in vec2 v_uv;
+
+out f16vec4 frag_color;
+
+void main() {
+  f16vec4 value = texture(glyph_atlas_sampler, v_uv);
+  frag_color = value * frag_info.text_color.aaaa;
+}