[vr] Add incognito coloring

chrome/browser/android/vr_shell/vr_shell_renderer.cc

 // Copyright 2016 The Chromium 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 "chrome/browser/android/vr_shell/vr_shell_renderer.h"
 
 #include <math.h>
 #include <algorithm>
 #include <string>
 
@@ skipping 120 matching lines @@
           uniform vec4 u_CopyRect;  // rectangle
           varying vec2 v_TexCoordinate;
           uniform lowp vec4 color;
           uniform mediump float opacity;
 
           void main() {
             vec2 scaledTex =
                 vec2(u_CopyRect[0] + v_TexCoordinate.x * u_CopyRect[2],
                      u_CopyRect[1] + v_TexCoordinate.y * u_CopyRect[3]);
             lowp vec4 color = texture2D(u_Texture, scaledTex);
-            gl_FragColor = vec4(color.xyz, color.w * opacity);
+            // premultiply opacity

[tiborg, 2017/05/25 00:47:18]

Nit: capital P and period in the end.

+            gl_FragColor = color * opacity;
           }
           /* clang-format on */);
     case vr_shell::ShaderID::WEBVR_VERTEX_SHADER:
       return SHADER(
           /* clang-format off */
           precision mediump float;
           attribute vec3 a_Position;
           attribute vec2 a_TexCoordinate;
           varying highp vec2 v_TexCoordinate;
 
@@ skipping 92 matching lines @@
     case vr_shell::ShaderID::CONTROLLER_FRAGMENT_SHADER:
       return SHADER(
           /* clang-format off */
           precision mediump float;
           uniform sampler2D u_texture;
           varying vec2 v_TexCoordinate;
           uniform mediump float u_Opacity;
 
           void main() {
             lowp vec4 texture_color = texture2D(u_texture, v_TexCoordinate);
-            gl_FragColor = vec4(texture_color.xyz, texture_color.w * u_Opacity);
+            // premultiply alpha

[tiborg, 2017/05/25 00:47:18]

Here too.

+            gl_FragColor = texture_color * u_Opacity;
           }
           /* clang-format on */);
     default:
       LOG(ERROR) << "Shader source requested for unknown shader";
       return "";
   }
 }
 
 }  // namespace
 
@@ skipping 143 matching lines @@
                         VOID_OFFSET(kPositionDataOffset));
   glEnableVertexAttribArray(position_handle_);
 
   // Set up texture coordinate attribute.
   glVertexAttribPointer(tex_coord_handle_, kTextureCoordinateDataSize, GL_FLOAT,
                         false, kTextureQuadDataStride,
                         VOID_OFFSET(kTextureCoordinateDataOffset));
   glEnableVertexAttribArray(tex_coord_handle_);
 
   glEnable(GL_BLEND);
-  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+  // Our textures have premultiplied alpha

[tiborg, 2017/05/25 00:47:18]

Nit: period in the end.

+  glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 
   // Link texture data with texture unit.
   glActiveTexture(GL_TEXTURE0);
   glUniform1i(tex_uniform_handle_, 0);
 
   // TODO(bajones): This should eventually be changed to use instancing so that
   // the entire queue can be processed in one draw call. For now this still
   // significantly reduces the amount of state changes made per draw.
   while (!quad_queue_.empty()) {
     const SkiaQuad& quad = quad_queue_.front();
@@ skipping 231 matching lines @@
   glVertexAttribPointer(position_handle_, position_components_, position_type_,
                         GL_FALSE, position_stride_, position_offset_);
   glEnableVertexAttribArray(position_handle_);
 
   glVertexAttribPointer(tex_coord_handle_, tex_coord_components_,
                         tex_coord_type_, GL_FALSE, tex_coord_stride_,
                         tex_coord_offset_);
   glEnableVertexAttribArray(tex_coord_handle_);
 
   glEnable(GL_BLEND);
-  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+  // Our textures have premultiplied alpha.
+  glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 
   glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indices_buffer_);
 
   glActiveTexture(GL_TEXTURE0);
   glBindTexture(GL_TEXTURE_2D, texture_handles_[state]);
   glUniform1i(tex_uniform_handle_, 0);
 
   glDrawElements(draw_mode_, indices_count_, indices_type_, indices_offset_);
 }
 
@@ skipping 171 matching lines @@
 GradientGridRenderer* VrShellRenderer::GetGradientGridRenderer() {
   Flush();
   return gradient_grid_renderer_.get();
 }
 
 void VrShellRenderer::Flush() {
   textured_quad_renderer_->Flush();
 }
 
 }  // namespace vr_shell