Fix gpu mipmap support on ChromeOS

gpu/command_buffer/service/texture_manager.cc

 // Copyright (c) 2012 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 "gpu/command_buffer/service/texture_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2864 matching lines @@
 
 // static
 GLenum TextureManager::AdjustTexInternalFormat(
     const gles2::FeatureInfo* feature_info,
     GLenum format) {
   if (feature_info->gl_version_info().is_desktop_core_profile) {
     const Texture::CompatibilitySwizzle* swizzle =
         GetCompatibilitySwizzle(format);
     if (swizzle)
       return swizzle->dest_format;
+
+    // Compatibility format substitutions that do not require swizzling
+    if (format == GL_BGRA_EXT)
+      return GL_RGBA;
+    if (format == GL_BGRA8_EXT)
+      return GL_RGBA8;

[piman, 2016/07/19 20:32:30]

This transformation should already happen at a lower level - see
GetTexInternalFormat/GetInternalFormat in ui/gl/gl_gl_api_implementation.cc.
What is it that requires this?

(in the future, I want to coalesce all this, see also crbug.com/628064, but for
now I'd prefer keeping these things in a single place, otherwise it gets super
confusing).

[Justin Novosad, 2016/07/19 21:45:25]

Thanks for pointing this out. I did a bit of investigation and I found that on
ChromeOS (ozone) the gl implementation gets set to kGLImplementationEGLGLES2,
which prevents the substitution from happening in GetInternalFormat

I don't know enough about the ChromeOS config, but could this be a
misrepresentation of the Mesa driver?  make an exception for Mesa?

[piman, 2016/07/19 21:56:08]

Ah, Ozone indeed does use the ES backend of Mesa. This substitution would be
illegal on ES2 + GL_EXT_texture_format_BGRA8888.

If Mesa expects RGBA instead of BGRA as the internal format, it sounds like a
driver bug? If so we would need to add a workaround entry, and only do this
transformation if the workaround is active.

   }
+
   return format;
 }
 
 // static
 GLenum TextureManager::AdjustTexFormat(const gles2::FeatureInfo* feature_info,
                                        GLenum format) {
   // TODO(bajones): GLES 3 allows for internal format and format to differ.
   // This logic may need to change as a result.
   if (!feature_info->gl_version_info().is_es) {
     if (format == GL_SRGB_EXT)
@@ skipping 468 matching lines @@
 uint32_t TextureManager::GetServiceIdGeneration() const {
   return current_service_id_generation_;
 }
 
 void TextureManager::IncrementServiceIdGeneration() {
   current_service_id_generation_++;
 }
 
 }  // namespace gles2
 }  // namespace gpu