gpu, cmaa: optimize COMBINE_EDGES path to reduce fragment shader tasks

gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc

Index: gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc b/gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc
index 65eca9ad36afcc8233508bcb22a70cae8970dcdb..71efc7f415fe5b43fcb28a73038de010f7264ada 100644
--- a/gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc
+++ b/gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.cc
@@ -348,8 +348,7 @@ void ApplyFramebufferAttachmentCMAAINTELResourceManager::ApplyCMAAEffectTexture(
 
   {
     glUseProgram(edges0_shader_);
-    glUniform1f(0, 1.0f);
-    glUniform2f(1, 1.0f / width_, 1.0f / height_);
+    glUniform2f(0, 1.0f / width_, 1.0f / height_);
     glDepthMask(GL_TRUE);
     glDepthFunc(GL_ALWAYS);
     glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
@@ -378,8 +377,7 @@ void ApplyFramebufferAttachmentCMAAINTELResourceManager::ApplyCMAAEffectTexture(
   //  image2D g_resultTexture             edge_texture_b               image0
   {
     glUseProgram(edges1_shader_);
-    glUniform1f(0, 0.0f);
-    glUniform2f(1, 1.0f / width_, 1.0f / height_);
+    glUniform2f(0, 1.0f / width_, 1.0f / height_);
     glDepthMask(GL_FALSE);
     glDepthFunc(GL_LESS);
     glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
@@ -399,9 +397,7 @@ void ApplyFramebufferAttachmentCMAAINTELResourceManager::ApplyCMAAEffectTexture(
   }
 
   //  - Combine RightBottom (.xy) edges from previous pass into
-  //    RightBottomLeftTop (.xyzw) edges and output it into the mask (have to
-  //    fill in the whole buffer including empty ones for the line length
-  //    detection to work correctly).
+  //    RightBottomLeftTop (.xyzw) edges and output it into the mask.
   //  - On all pixels with any edge, input buffer into a temporary color buffer
   //    needed for correct blending in the next pass (other pixels not needed
   //    so not copied to avoid bandwidth use).
@@ -415,13 +411,12 @@ void ApplyFramebufferAttachmentCMAAINTELResourceManager::ApplyCMAAEffectTexture(
   //  gl_FragDepth                        mini4_edge_texture_          fbo.depth
   {
     // Combine edges: each pixel will now contain info on all (top, right,
-    // bottom, left) edges; also create depth mask as above depth and mark
-    // potential Z sAND also copy source color data but only on edge pixels
+    // bottom, left) edges; also mark depth 1 value on all pixels with any edge
+    // and also copy source color data but only on edge pixels
     glUseProgram(edges_combine_shader_);
-    glUniform1f(0, 1.0f);
-    glUniform2f(1, 1.0f / width_, 1.0f / height_);
+    glUniform2f(0, 1.0f / width_, 1.0f / height_);
     glDepthMask(GL_TRUE);
-    glDepthFunc(GL_ALWAYS);
+    glDepthFunc(GL_LESS);
     glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
 
     if (!is_gles31_compatible_) {
@@ -455,8 +450,7 @@ void ApplyFramebufferAttachmentCMAAINTELResourceManager::ApplyCMAAEffectTexture(
   //  gl_FragDepth                         mini4_edge_texture_         fbo.depth
   {
     glUseProgram(process_and_apply_shader_);
-    glUniform1f(0, 0.0f);
-    glUniform2f(1, 1.0f / width_, 1.0f / height_);
+    glUniform2f(0, 1.0f / width_, 1.0f / height_);
     glDepthMask(GL_FALSE);
     glDepthFunc(GL_LESS);
     glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
@@ -690,7 +684,6 @@ GLuint ApplyFramebufferAttachmentCMAAINTELResourceManager::CreateShader(
 const char ApplyFramebufferAttachmentCMAAINTELResourceManager::vert_str_[] =
   SHADER(
     precision highp float;
-    layout(location = 0) uniform float g_Depth;
     // No input data.
     // Verts are autogenerated.
     //
@@ -703,7 +696,7 @@ const char ApplyFramebufferAttachmentCMAAINTELResourceManager::vert_str_[] =
     {
        float x = -1.0 + float((gl_VertexID & 1) << 2);
        float y = -1.0 + float((gl_VertexID & 2) << 1);
-       gl_Position = vec4(x, y, g_Depth, 1.0);
+       gl_Position = vec4(x, y, 0.0, 1.0);
     }
   );
 
@@ -716,12 +709,10 @@ const char ApplyFramebufferAttachmentCMAAINTELResourceManager::cmaa_frag_s1_[] =
     \n#define EDGE_DETECT_THRESHOLD 13.0f\n
     \n#define saturate(x) clamp((x), 0.0, 1.0)\n
 
-    // bind to location 0
-    layout(location = 0) uniform float g_Depth;
     // bind to a uniform buffer bind point 0
-    layout(location = 1) uniform vec2 g_OneOverScreenSize;
+    layout(location = 0) uniform vec2 g_OneOverScreenSize;
     \n#ifndef EDGE_DETECT_THRESHOLD\n
-    layout(location = 2) uniform float g_ColorThreshold;
+    layout(location = 1) uniform float g_ColorThreshold;
     \n#endif\n
 
     \n#ifdef SUPPORTS_USAMPLER2D\n