Re-land^2 WebVR compositor bypass via BrowserMain context + mailbox

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 388 matching lines @@
                         kTextureQuadDataStride,
                         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_);
 
-  // Bind texture. Ideally this should be a 1:1 pixel copy. (Or even more
-  // ideally, a zero copy reuse of the texture.) For now, we're using an
-  // undersized render target for WebVR, so GL_LINEAR makes it look slightly
-  // less chunky. TODO(klausw): change this to GL_NEAREST once we're doing
-  // a 1:1 copy since that should be more efficient.
+  // Bind texture. This is a 1:1 pixel copy since the source surface
+  // and renderbuffer destination size are resized to match, so use
+  // GL_NEAREST.
   glActiveTexture(GL_TEXTURE0);
   glBindTexture(GL_TEXTURE_EXTERNAL_OES, texture_handle);
   glTexParameteri(GL_TEXTURE_EXTERNAL_OES, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
   glTexParameteri(GL_TEXTURE_EXTERNAL_OES, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
   glTexParameteri(GL_TEXTURE_EXTERNAL_OES, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
   glTexParameteri(GL_TEXTURE_EXTERNAL_OES, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
   glUniform1i(tex_uniform_handle_, 0);
 
   // Blit texture to buffer
   glDrawArrays(GL_TRIANGLES, 0, kVerticesNumber);
@@ skipping 212 matching lines @@
     : textured_quad_renderer_(new TexturedQuadRenderer),
       webvr_renderer_(new WebVrRenderer),
       reticle_renderer_(new ReticleRenderer),
       laser_renderer_(new LaserRenderer),
       gradient_quad_renderer_(new GradientQuadRenderer),
       gradient_grid_renderer_(new GradientGridRenderer) {}
 
 VrShellRenderer::~VrShellRenderer() = default;
 
 }  // namespace vr_shell