Implement native GMB backbuffers in the GLES2 Command Decoder.

gpu/command_buffer/service/gles2_cmd_decoder.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/gles2_cmd_decoder.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
@@ skipping 30 matching lines @@
 #include "gpu/command_buffer/service/gl_utils.h"
 #include "gpu/command_buffer/service/gles2_cmd_apply_framebuffer_attachment_cmaa_intel.h"
 #include "gpu/command_buffer/service/gles2_cmd_clear_framebuffer.h"
 #include "gpu/command_buffer/service/gles2_cmd_copy_tex_image.h"
 #include "gpu/command_buffer/service/gles2_cmd_copy_texture_chromium.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder_passthrough.h"
 #include "gpu/command_buffer/service/gles2_cmd_validation.h"
 #include "gpu/command_buffer/service/gpu_preferences.h"
 #include "gpu/command_buffer/service/gpu_state_tracer.h"
 #include "gpu/command_buffer/service/gpu_tracer.h"
+#include "gpu/command_buffer/service/image_factory.h"
 #include "gpu/command_buffer/service/image_manager.h"
 #include "gpu/command_buffer/service/logger.h"
 #include "gpu/command_buffer/service/mailbox_manager.h"
 #include "gpu/command_buffer/service/memory_tracking.h"
 #include "gpu/command_buffer/service/path_manager.h"
 #include "gpu/command_buffer/service/program_manager.h"
 #include "gpu/command_buffer/service/query_manager.h"
 #include "gpu/command_buffer/service/renderbuffer_manager.h"
 #include "gpu/command_buffer/service/sampler_manager.h"
 #include "gpu/command_buffer/service/shader_manager.h"
 #include "gpu/command_buffer/service/shader_translator.h"
 #include "gpu/command_buffer/service/texture_manager.h"
 #include "gpu/command_buffer/service/transform_feedback_manager.h"
 #include "gpu/command_buffer/service/vertex_array_manager.h"
 #include "gpu/command_buffer/service/vertex_attrib_manager.h"
 #include "third_party/smhasher/src/City.h"
+#include "ui/gfx/buffer_types.h"
 #include "ui/gfx/geometry/point.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/size.h"
+#include "ui/gfx/gpu_memory_buffer.h"
 #include "ui/gfx/overlay_transform.h"
 #include "ui/gfx/transform.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_context.h"
 #include "ui/gl/gl_fence.h"
 #include "ui/gl/gl_image.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"
 #include "ui/gl/gl_version_info.h"
 #include "ui/gl/gpu_timing.h"
@@ skipping 320 matching lines @@
   void Copy(const gfx::Size& size, GLenum format);
 
   // Destroy the render texture. This must be explicitly called before
   // destroying this object.
   void Destroy();
 
   // Invalidate the texture. This can be used when a context is lost and it is
   // not possible to make it current in order to free the resource.
   void Invalidate();
 
+  // The bind point for the texture.
+  GLenum Target();
+
   scoped_refptr<TextureRef> texture_ref() { return texture_ref_; }
 
   GLuint id() const {
     return texture_ref_ ? texture_ref_->service_id() : 0;
   }
 
   gfx::Size size() const {
     return size_;
   }
 
  private:
+  // The texture must be bound to Target() before calling this method.
+  void AllocateNativeGpuMemoryBuffer(const gfx::Size& size,
+                                     GLenum format,
+                                     bool zero);
+
+  // The texture must be bound to Target() before calling this method.
+  void DestroyNativeGpuMemoryBuffer(bool have_context);
+
   MemoryTypeTracker memory_tracker_;
   size_t bytes_allocated_;
   gfx::Size size_;
   GLES2DecoderImpl* decoder_;
 
   scoped_refptr<TextureRef> texture_ref_;
 
+  // The image that backs the texture, if its backed by a native
+  // GpuMemoryBuffer.
+  scoped_refptr<gl::GLImage> image_;
+
   DISALLOW_COPY_AND_ASSIGN(BackTexture);
 };
 
 // Encapsulates an OpenGL render buffer of any format.
 class BackRenderbuffer {
  public:
-  explicit BackRenderbuffer(
-      RenderbufferManager* renderbuffer_manager,
-      MemoryTracker* memory_tracker,
-      ContextState* state);
+  explicit BackRenderbuffer(GLES2DecoderImpl* decoder);
   ~BackRenderbuffer();
 
   // Create a new render buffer.
   void Create();
 
   // Set the initial size and format of a render buffer or resize it.
   bool AllocateStorage(const FeatureInfo* feature_info,
                        const gfx::Size& size,
                        GLenum format,
                        GLsizei samples);
 
   // Destroy the render buffer. This must be explicitly called before destroying
   // this object.
   void Destroy();
 
   // Invalidate the render buffer. This can be used when a context is lost and
   // it is not possible to make it current in order to free the resource.
   void Invalidate();
 
   GLuint id() const {
     return id_;
   }
 
  private:
-  RenderbufferManager* renderbuffer_manager_;
+  GLES2DecoderImpl* decoder_;
   MemoryTypeTracker memory_tracker_;
-  ContextState* state_;
   size_t bytes_allocated_;
   GLuint id_;
   DISALLOW_COPY_AND_ASSIGN(BackRenderbuffer);
 };
 
 // Encapsulates an OpenGL frame buffer.
 class BackFramebuffer {
  public:
   explicit BackFramebuffer(GLES2DecoderImpl* decoder);
   ~BackFramebuffer();
@@ skipping 189 matching lines @@
 
   // Restores the current state to the user's settings.
   void RestoreCurrentFramebufferBindings();
 
   // Sets DEPTH_TEST, STENCIL_TEST and color mask for the current framebuffer.
   void ApplyDirtyState();
 
   // These check the state of the currently bound framebuffer or the
   // backbuffer if no framebuffer is bound.
   // Check with all attached and enabled color attachments.
-  bool BoundFramebufferHasColorAttachmentWithAlpha();
+  bool BoundFramebufferAllowsChangesToAlphaChannel();
   bool BoundFramebufferHasDepthAttachment();
   bool BoundFramebufferHasStencilAttachment();
 
   error::ContextLostReason GetContextLostReason() override;
 
   // Overriden from ErrorStateClient.
   void OnContextLostError() override;
   void OnOutOfMemoryError() override;
 
   // Ensure Renderbuffer corresponding to last DoBindRenderbuffer() is bound.
@@ skipping 19 matching lines @@
                              GLbitfield mask,
                              GLenum filter);
 
   PathManager* path_manager() { return group_->path_manager(); }
 
  private:
   friend class ScopedFrameBufferBinder;
   friend class ScopedFrameBufferReadPixelHelper;
   friend class ScopedResolvedFrameBufferBinder;
   friend class BackFramebuffer;
+  friend class BackRenderbuffer;
   friend class BackTexture;
 
   enum FramebufferOperation {
     kFramebufferDiscard,
     kFramebufferInvalidate,
     kFramebufferInvalidateSub
   };
 
   enum BindIndexedBufferFunctionType {
     kBindBufferBase,
@@ skipping 1217 matching lines @@
   error::Error WillAccessBoundFramebufferForRead() {
     if (ShouldDeferReads())
       return error::kDeferCommandUntilLater;
     if (!offscreen_target_frame_buffer_.get() &&
         !framebuffer_state_.bound_read_framebuffer.get() &&
         !surface_->SetBackbufferAllocation(true))
       return error::kLostContext;
     return error::kNoError;
   }
 
-  bool BackBufferHasAlpha() const {
+  // Whether the back buffer exposed to the client has an alpha channel. Note
+  // that this is potentially different from whether the implementation of the
+  // back buffer has an alpha channel.
+  bool ClientExposedBackBufferHasAlpha() const {
     if (back_buffer_draw_buffer_ == GL_NONE)
       return false;
     if (offscreen_target_frame_buffer_.get()) {
-      return (offscreen_target_color_format_ == GL_RGBA ||
-              offscreen_target_color_format_ == GL_RGBA8);
+      return offscreen_buffer_should_have_alpha_;
     }
     return (back_buffer_color_format_ == GL_RGBA ||
             back_buffer_color_format_ == GL_RGBA8);
   }
 
+  // If the back buffer has a non-emulated alpha channel, the clear color should
+  // be 0. Otherwise, the clear color should be 1.
+  GLfloat BackBufferAlphaClearColor() const {
+    return offscreen_buffer_should_have_alpha_ ? 0.f : 1.f;
+  }
+
   // Set remaining commands to process to 0 to force DoCommands to return
   // and allow context preemption and GPU watchdog checks in CommandExecutor().
   void ExitCommandProcessingEarly() { commands_to_process_ = 0; }
 
   void ProcessPendingReadPixels(bool did_finish);
   void FinishReadPixels(const cmds::ReadPixels& c, GLuint buffer);
 
   // Checks to see if the inserted fence has completed.
   void ProcessDescheduleUntilFinished();
 
   void DoBindFragmentInputLocationCHROMIUM(GLuint program_id,
                                            GLint location,
                                            const std::string& name);
 
   // If |texture_manager_version_| doesn't match the current version, then this
   // will rebind all external textures to match their current service_id.
   void RestoreAllExternalTextureBindingsIfNeeded() override;
 
   const SamplerState& GetSamplerStateForTextureUnit(GLenum target, GLuint unit);
 
   // copyTexImage2D doesn't work on OSX under very specific conditions.
   // Returns whether those conditions have been met. If this method returns
   // true, |source_texture_service_id| and |source_texture_target| are also
   // populated, since they are needed to implement the workaround.
   bool NeedsCopyTextureImageWorkaround(GLenum internal_format,
                                        int32_t channels_exist,
                                        GLuint* source_texture_service_id,
                                        GLenum* source_texture_target);
 
+  // Whether a texture backed by a Chromium Image needs to emulate GL_RGB format
+  // using GL_RGBA and glColorMask.
+  bool ChromiumImageNeedsRGBEmulation();
+
   bool InitializeCopyTexImageBlitter(const char* function_name);
   bool InitializeCopyTextureCHROMIUM(const char* function_name);
   // Generate a member function prototype for each command in an automated and
   // typesafe way.
 #define GLES2_CMD_OP(name) \
   Error Handle##name(uint32_t immediate_data_size, const void* data);
 
   GLES2_COMMAND_LIST(GLES2_CMD_OP)
 
   #undef GLES2_CMD_OP
@@ skipping 39 matching lines @@
 
   // The offscreen frame buffer that the client renders to. With EGL, the
   // depth and stencil buffers are separate. With regular GL there is a single
   // packed depth stencil buffer in offscreen_target_depth_render_buffer_.
   // offscreen_target_stencil_render_buffer_ is unused.
   std::unique_ptr<BackFramebuffer> offscreen_target_frame_buffer_;
   std::unique_ptr<BackTexture> offscreen_target_color_texture_;
   std::unique_ptr<BackRenderbuffer> offscreen_target_color_render_buffer_;
   std::unique_ptr<BackRenderbuffer> offscreen_target_depth_render_buffer_;
   std::unique_ptr<BackRenderbuffer> offscreen_target_stencil_render_buffer_;
+
+  // The format of the texture or renderbuffer backing the offscreen
+  // framebuffer. Also the format of the texture backing the saved offscreen
+  // framebuffer.
   GLenum offscreen_target_color_format_;
+
   GLenum offscreen_target_depth_format_;
   GLenum offscreen_target_stencil_format_;
   GLsizei offscreen_target_samples_;
   GLboolean offscreen_target_buffer_preserved_;
 
   // The saved copy of the backbuffer after a call to SwapBuffers.
   std::unique_ptr<BackTexture> offscreen_saved_color_texture_;
 
   // For simplicity, |offscreen_saved_color_texture_| is always bound to
   // |offscreen_saved_frame_buffer_|.
@@ skipping 23 matching lines @@
   void ReleaseAllBackTextures(bool have_context);
 
   size_t GetSavedBackTextureCountForTest() override;
   size_t GetCreatedBackTextureCountForTest() override;
 
   // The copy that is used as the destination for multi-sample resolves.
   std::unique_ptr<BackFramebuffer> offscreen_resolved_frame_buffer_;
   std::unique_ptr<BackTexture> offscreen_resolved_color_texture_;
   GLenum offscreen_saved_color_format_;
 
+  // Whether the client requested an offscreen buffer with an alpha channel.
+  bool offscreen_buffer_should_have_alpha_;
+
   std::unique_ptr<QueryManager> query_manager_;
 
   std::unique_ptr<VertexArrayManager> vertex_array_manager_;
 
   std::unique_ptr<ImageManager> image_manager_;
 
   FenceSyncReleaseCallback fence_sync_release_callback_;
   WaitFenceSyncCallback wait_fence_sync_callback_;
   NoParamCallback deschedule_until_finished_callback_;
   NoParamCallback reschedule_after_finished_callback_;
@@ skipping 54 matching lines @@
   bool derivatives_explicitly_enabled_;
   bool frag_depth_explicitly_enabled_;
   bool draw_buffers_explicitly_enabled_;
   bool shader_texture_lod_explicitly_enabled_;
 
   bool compile_shader_always_succeeds_;
 
   // An optional behaviour to lose the context and group when OOM.
   bool lose_context_when_out_of_memory_;
 
+  // Forces the backbuffer to use native GMBs rather than a TEXTURE_2D texture.
+  bool should_use_native_gmb_for_backbuffer_;
+
   // Log extra info.
   bool service_logging_;
 
   std::unique_ptr<ApplyFramebufferAttachmentCMAAINTELResourceManager>
       apply_framebuffer_attachment_cmaa_intel_;
   std::unique_ptr<CopyTexImageResourceManager> copy_tex_image_blit_;
   std::unique_ptr<CopyTextureCHROMIUMResourceManager> copy_texture_CHROMIUM_;
   std::unique_ptr<ClearFramebufferResourceManager> clear_framebuffer_blit_;
 
   // Cached values of the currently assigned viewport dimensions.
@@ skipping 145 matching lines @@
     GLES2DecoderImpl* decoder, bool enforce_internal_framebuffer, bool internal)
     : decoder_(decoder) {
   resolve_and_bind_ = (
       decoder_->offscreen_target_frame_buffer_.get() &&
       decoder_->IsOffscreenBufferMultisampled() &&
       (!decoder_->framebuffer_state_.bound_read_framebuffer.get() ||
        enforce_internal_framebuffer));
   if (!resolve_and_bind_)
     return;
 
+  // TODO(erikchen): On old AMD GPUs on macOS, glColorMask doesn't work
+  // correctly for multisampled renderbuffers and the alpha channel can be
+  // overwritten. Add a workaround to clear the alpha channel before resolving.
+  // https://crbug.com/602484.
   ScopedGLErrorSuppressor suppressor(
       "ScopedResolvedFrameBufferBinder::ctor", decoder_->GetErrorState());
   glBindFramebufferEXT(GL_READ_FRAMEBUFFER_EXT,
                        decoder_->offscreen_target_frame_buffer_->id());
   GLuint targetid;
   if (internal) {
     if (!decoder_->offscreen_resolved_frame_buffer_.get()) {
       decoder_->offscreen_resolved_frame_buffer_.reset(
           new BackFramebuffer(decoder_));
       decoder_->offscreen_resolved_frame_buffer_->Create();
@@ skipping 15 matching lines @@
       }
     }
     targetid = decoder_->offscreen_resolved_frame_buffer_->id();
   } else {
     targetid = decoder_->offscreen_saved_frame_buffer_->id();
   }
   glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER_EXT, targetid);
   const int width = decoder_->offscreen_size_.width();
   const int height = decoder_->offscreen_size_.height();
   decoder->state_.SetDeviceCapabilityState(GL_SCISSOR_TEST, false);
+  glBindFramebufferEXT(GL_DRAW_FRAMEBUFFER_EXT, targetid);

[piman, 2016/06/27 19:37:36]

nit: this was already done on l.2406

[erikchen, 2016/06/27 22:16:03]

Removed.

   decoder->BlitFramebufferHelper(0,
                                  0,
                                  width,
                                  height,
                                  0,
                                  0,
                                  width,
                                  height,
                                  GL_COLOR_BUFFER_BIT,
                                  GL_NEAREST);
@@ skipping 50 matching lines @@
 BackTexture::BackTexture(GLES2DecoderImpl* decoder)
     : memory_tracker_(decoder->memory_tracker()),
       bytes_allocated_(0),
       decoder_(decoder) {}
 
 BackTexture::~BackTexture() {
   // This does not destroy the render texture because that would require that
   // the associated GL context was current. Just check that it was explicitly
   // destroyed.
   DCHECK_EQ(id(), 0u);
+  DCHECK(!image_.get());
 }
 
 void BackTexture::Create() {
   DCHECK_EQ(id(), 0u);
   ScopedGLErrorSuppressor suppressor("BackTexture::Create",
                                      decoder_->state_.GetErrorState());
   GLuint id;
   glGenTextures(1, &id);
 
-  GLenum target = GL_TEXTURE_2D;
+  GLenum target = Target();
   ScopedTextureBinder binder(&decoder_->state_, id, target);
 
   // No client id is necessary because this texture will never be directly
   // accessed by a client, only indirectly via a mailbox.
   texture_ref_ = TextureRef::Create(decoder_->texture_manager(), 0, id);
   decoder_->texture_manager()->SetTarget(texture_ref_.get(), target);
   decoder_->texture_manager()->SetParameteri(
       "BackTexture::Create",
       decoder_->GetErrorState(),
       texture_ref_.get(),
@@ skipping 17 matching lines @@
       texture_ref_.get(),
       GL_TEXTURE_WRAP_T,
       GL_CLAMP_TO_EDGE);
 }
 
 bool BackTexture::AllocateStorage(
     const gfx::Size& size, GLenum format, bool zero) {
   DCHECK_NE(id(), 0u);
   ScopedGLErrorSuppressor suppressor("BackTexture::AllocateStorage",
                                      decoder_->state_.GetErrorState());
-  ScopedTextureBinder binder(&decoder_->state_, id(), GL_TEXTURE_2D);
+  ScopedTextureBinder binder(&decoder_->state_, id(), Target());
   uint32_t image_size = 0;
   GLES2Util::ComputeImageDataSizes(
       size.width(), size.height(), 1, format, GL_UNSIGNED_BYTE, 8, &image_size,
       NULL, NULL);
 
   if (!memory_tracker_.EnsureGPUMemoryAvailable(image_size)) {
     return false;
   }
 
-  std::unique_ptr<char[]> zero_data;
-  if (zero) {
-    zero_data.reset(new char[image_size]);
-    memset(zero_data.get(), 0, image_size);
+  size_ = size;
+  if (decoder_->should_use_native_gmb_for_backbuffer_) {
+    DestroyNativeGpuMemoryBuffer(true);
+    AllocateNativeGpuMemoryBuffer(size, format, zero);
+  } else {
+    std::unique_ptr<char[]> zero_data;
+    if (zero) {
+      zero_data.reset(new char[image_size]);
+      memset(zero_data.get(), 0, image_size);
+    }
+
+    glTexImage2D(Target(),
+                 0,  // mip level
+                 format, size.width(), size.height(),
+                 0,  // border
+                 format, GL_UNSIGNED_BYTE, zero_data.get());
+    decoder_->texture_manager()->SetLevelInfo(
+        texture_ref_.get(), Target(),
+        0,  // level
+        GL_RGBA, size.width(), size.height(),
+        1,  // depth
+        0,  // border
+        GL_RGBA, GL_UNSIGNED_BYTE, gfx::Rect(size));
   }
 
-  glTexImage2D(GL_TEXTURE_2D,
-               0,  // mip level
-               format,
-               size.width(),
-               size.height(),
-               0,  // border
-               format,
-               GL_UNSIGNED_BYTE,
-               zero_data.get());
-
-  size_ = size;
-  decoder_->texture_manager()->SetLevelInfo(texture_ref_.get(), GL_TEXTURE_2D,
-      0,  // level
-      GL_RGBA, size_.width(), size_.height(),
-      1,  // depth
-      0,  // border
-      GL_RGBA, GL_UNSIGNED_BYTE, gfx::Rect(size_));
-
   bool success = glGetError() == GL_NO_ERROR;
   if (success) {
     memory_tracker_.TrackMemFree(bytes_allocated_);
     bytes_allocated_ = image_size;
     memory_tracker_.TrackMemAlloc(bytes_allocated_);
   }
   return success;
 }
 
 void BackTexture::Copy(const gfx::Size& size, GLenum format) {
   DCHECK_NE(id(), 0u);
   ScopedGLErrorSuppressor suppressor("BackTexture::Copy",
                                      decoder_->state_.GetErrorState());
-  ScopedTextureBinder binder(&decoder_->state_, id(), GL_TEXTURE_2D);
-  glCopyTexImage2D(GL_TEXTURE_2D,
+  ScopedTextureBinder binder(&decoder_->state_, id(), Target());
+  glCopyTexImage2D(Target(),
                    0,  // level
-                   format,
-                   0, 0,
-                   size.width(),
-                   size.height(),
+                   format, 0, 0, size.width(), size.height(),
                    0);  // border
 }
 
 void BackTexture::Destroy() {
+  if (image_) {
+    DCHECK(texture_ref_);
+    ScopedTextureBinder binder(&decoder_->state_, id(), Target());
+    DestroyNativeGpuMemoryBuffer(true);
+  }
+
   if (texture_ref_) {
     ScopedGLErrorSuppressor suppressor("BackTexture::Destroy",
                                        decoder_->state_.GetErrorState());
     texture_ref_ = nullptr;
   }
   memory_tracker_.TrackMemFree(bytes_allocated_);
   bytes_allocated_ = 0;
 }
 
 void BackTexture::Invalidate() {
+  if (image_) {
+    DestroyNativeGpuMemoryBuffer(false);
+    image_ = nullptr;
+  }
   if (texture_ref_) {
     texture_ref_->ForceContextLost();
     texture_ref_ = nullptr;
   }
 }
 
-BackRenderbuffer::BackRenderbuffer(
-    RenderbufferManager* renderbuffer_manager,
-    MemoryTracker* memory_tracker,
-    ContextState* state)
-    : renderbuffer_manager_(renderbuffer_manager),
-      memory_tracker_(memory_tracker),
-      state_(state),
+GLenum BackTexture::Target() {
+  // TODO(erikchen): Make this method more robust by not assuming that a native
+  // GMB has target GL_TEXTURE_RECTANGLE_ARB.
+  return decoder_->should_use_native_gmb_for_backbuffer_
+             ? GL_TEXTURE_RECTANGLE_ARB

[piman, 2016/06/27 19:37:36]

nit: could the target be given by the ImageFactory?

[erikchen, 2016/06/27 22:16:03]

Yes, Done

+             : GL_TEXTURE_2D;
+}
+
+void BackTexture::AllocateNativeGpuMemoryBuffer(const gfx::Size& size,
+                                                GLenum format,
+                                                bool zero) {
+  gfx::BufferFormat buffer_format = gfx::BufferFormat::RGBA_8888;
+  scoped_refptr<gl::GLImage> image =
+      decoder_->GetContextGroup()->image_factory()->CreateAnonymousImage(

[piman, 2016/06/27 19:37:36]

image_factory could be null.

[erikchen, 2016/06/27 22:16:04]

This gets DCHECKED in the constructor of BackTexture, and the real logic to
prevent this from happening lies in the Decoder initializer.

+          size, buffer_format, format);
+  if (!image->BindTexImage(Target()))

[piman, 2016/06/27 19:37:36]

image could be null if the ImageFactory doesn't support CreateAnonymousImage

[erikchen, 2016/06/27 22:16:04]

Added a conditional.

+    return;

[piman, 2016/06/27 19:37:36]

Can we forward the failure, so that we can e.g. lose the context instead of
silently failing?

[erikchen, 2016/06/27 22:16:03]

Done.

+
+  image_ = image;
+  decoder_->texture_manager()->SetLevelInfo(
+      texture_ref_.get(), Target(), 0, image_->GetInternalFormat(),
+      size.width(), size.height(), 1, 0, image_->GetInternalFormat(),
+      GL_UNSIGNED_BYTE, gfx::Rect(size));
+  decoder_->texture_manager()->SetLevelImage(texture_ref_.get(), Target(), 0,
+                                             image_.get(), Texture::BOUND);
+
+  // Ignore the zero flag if the alpha channel needs to be cleared for RGB
+  // emulation.
+  bool needs_clear_for_rgb_emulation =
+      !decoder_->offscreen_buffer_should_have_alpha_ &&
+      decoder_->ChromiumImageNeedsRGBEmulation();
+  if (zero || needs_clear_for_rgb_emulation) {
+    GLuint fbo;
+    glGenFramebuffersEXT(1, &fbo);
+    {
+      ScopedFrameBufferBinder binder(decoder_, fbo);
+      glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, Target(),
+                                id(), 0);
+      glClearColor(0, 0, 0, decoder_->BackBufferAlphaClearColor());
+      decoder_->state_.SetDeviceColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+      decoder_->state_.SetDeviceCapabilityState(GL_SCISSOR_TEST, false);
+      glClear(GL_COLOR_BUFFER_BIT);
+      decoder_->RestoreClearState();
+      glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, Target(),
+                                0, 0);

[piman, 2016/06/27 19:37:36]

nit: is this necessary? You're about to destroy the fbo.

[erikchen, 2016/06/27 22:16:04]

No, removed.

+    }
+    glDeleteFramebuffersEXT(1, &fbo);
+  }
+}
+
+void BackTexture::DestroyNativeGpuMemoryBuffer(bool have_context) {
+  if (image_) {
+    ScopedGLErrorSuppressor suppressor(
+        "BackTexture::DestroyNativeGpuMemoryBuffer",
+        decoder_->state_.GetErrorState());
+
+    image_->ReleaseTexImage(Target());
+    image_->Destroy(have_context);
+
+    decoder_->texture_manager()->SetLevelImage(texture_ref_.get(), Target(), 0,
+                                               nullptr, Texture::UNBOUND);
+    image_ = nullptr;
+  }
+}
+
+BackRenderbuffer::BackRenderbuffer(GLES2DecoderImpl* decoder)
+    : decoder_(decoder),
+      memory_tracker_(decoder->memory_tracker()),
       bytes_allocated_(0),
-      id_(0) {
-}
+      id_(0) {}
 
 BackRenderbuffer::~BackRenderbuffer() {
   // This does not destroy the render buffer because that would require that
   // the associated GL context was current. Just check that it was explicitly
   // destroyed.
   DCHECK_EQ(id_, 0u);
 }
 
 void BackRenderbuffer::Create() {
   ScopedGLErrorSuppressor suppressor("BackRenderbuffer::Create",
-                                     state_->GetErrorState());
+                                     decoder_->state_.GetErrorState());
   Destroy();
   glGenRenderbuffersEXT(1, &id_);
 }
 
 bool BackRenderbuffer::AllocateStorage(const FeatureInfo* feature_info,
                                        const gfx::Size& size,
                                        GLenum format,
                                        GLsizei samples) {
-  ScopedGLErrorSuppressor suppressor(
-      "BackRenderbuffer::AllocateStorage", state_->GetErrorState());
-  ScopedRenderBufferBinder binder(state_, id_);
+  ScopedGLErrorSuppressor suppressor("BackRenderbuffer::AllocateStorage",
+                                     decoder_->state_.GetErrorState());
+  ScopedRenderBufferBinder binder(&decoder_->state_, id_);
 
   uint32_t estimated_size = 0;
-  if (!renderbuffer_manager_->ComputeEstimatedRenderbufferSize(
-           size.width(), size.height(), samples, format, &estimated_size)) {
+  if (!decoder_->renderbuffer_manager()->ComputeEstimatedRenderbufferSize(
+          size.width(), size.height(), samples, format, &estimated_size)) {
     return false;
   }
 
   if (!memory_tracker_.EnsureGPUMemoryAvailable(estimated_size)) {
     return false;
   }
 
   if (samples <= 1) {
     glRenderbufferStorageEXT(GL_RENDERBUFFER,
                              format,
                              size.width(),
                              size.height());
   } else {
     GLES2DecoderImpl::RenderbufferStorageMultisampleHelper(feature_info,
                                                            GL_RENDERBUFFER,
                                                            samples,
                                                            format,
                                                            size.width(),
                                                            size.height());
   }
+
+  bool alpha_channel_needs_clear =
+      (format == GL_RGBA || format == GL_RGBA8) &&
+      !decoder_->offscreen_buffer_should_have_alpha_;
+  if (alpha_channel_needs_clear) {
+    GLuint fbo;
+    glGenFramebuffersEXT(1, &fbo);
+    {
+      ScopedFrameBufferBinder binder(decoder_, fbo);
+      glFramebufferRenderbufferEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                                   GL_RENDERBUFFER, id_);
+      glClearColor(0, 0, 0, decoder_->BackBufferAlphaClearColor());
+      decoder_->state_.SetDeviceColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
+      decoder_->state_.SetDeviceCapabilityState(GL_SCISSOR_TEST, false);
+      glClear(GL_COLOR_BUFFER_BIT);
+      decoder_->RestoreClearState();
+      glFramebufferRenderbufferEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                                   GL_RENDERBUFFER, 0);

[piman, 2016/06/27 19:37:36]

nit: ditto.

[erikchen, 2016/06/27 22:16:03]

Done.

+    }
+    glDeleteFramebuffersEXT(1, &fbo);
+  }
+
   bool success = glGetError() == GL_NO_ERROR;
   if (success) {
     // Mark the previously allocated bytes as free.
     memory_tracker_.TrackMemFree(bytes_allocated_);
     bytes_allocated_ = estimated_size;
     // Track the newly allocated bytes.
     memory_tracker_.TrackMemAlloc(bytes_allocated_);
   }
   return success;
 }
 
 void BackRenderbuffer::Destroy() {
   if (id_ != 0) {
     ScopedGLErrorSuppressor suppressor("BackRenderbuffer::Destroy",
-                                       state_->GetErrorState());
+                                       decoder_->state_.GetErrorState());
     glDeleteRenderbuffersEXT(1, &id_);
     id_ = 0;
   }
   memory_tracker_.TrackMemFree(bytes_allocated_);
   bytes_allocated_ = 0;
 }
 
 void BackRenderbuffer::Invalidate() {
   id_ = 0;
 }
@@ skipping 16 matching lines @@
   Destroy();
   glGenFramebuffersEXT(1, &id_);
 }
 
 void BackFramebuffer::AttachRenderTexture(BackTexture* texture) {
   DCHECK_NE(id_, 0u);
   ScopedGLErrorSuppressor suppressor(
       "BackFramebuffer::AttachRenderTexture", decoder_->GetErrorState());
   ScopedFrameBufferBinder binder(decoder_, id_);
   GLuint attach_id = texture ? texture->id() : 0;
-  glFramebufferTexture2DEXT(GL_FRAMEBUFFER,
-                            GL_COLOR_ATTACHMENT0,
-                            GL_TEXTURE_2D,
-                            attach_id,
-                            0);
+  glFramebufferTexture2DEXT(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                            texture->Target(), attach_id, 0);
 }
 
 void BackFramebuffer::AttachRenderBuffer(GLenum target,
                                          BackRenderbuffer* render_buffer) {
   DCHECK_NE(id_, 0u);
   ScopedGLErrorSuppressor suppressor(
       "BackFramebuffer::AttachRenderBuffer", decoder_->GetErrorState());
   ScopedFrameBufferBinder binder(decoder_, id_);
   GLuint attach_id = render_buffer ? render_buffer->id() : 0;
   glFramebufferRenderbufferEXT(GL_FRAMEBUFFER,
@@ skipping 39 matching lines @@
       attrib_0_buffer_matches_value_(true),
       attrib_0_size_(0),
       fixed_attrib_buffer_id_(0),
       fixed_attrib_buffer_size_(0),
       offscreen_target_color_format_(0),
       offscreen_target_depth_format_(0),
       offscreen_target_stencil_format_(0),
       offscreen_target_samples_(0),
       offscreen_target_buffer_preserved_(true),
       offscreen_saved_color_format_(0),
+      offscreen_buffer_should_have_alpha_(false),
       back_buffer_color_format_(0),
       back_buffer_has_depth_(false),
       back_buffer_has_stencil_(false),
       back_buffer_read_buffer_(GL_BACK),
       back_buffer_draw_buffer_(GL_BACK),
       surfaceless_(false),
       backbuffer_needs_clear_bits_(0),
       swaps_since_resize_(0),
       current_decoder_error_(error::kNoError),
       validators_(group_->feature_info()->validators()),
       feature_info_(group_->feature_info()),
       frame_number_(0),
       has_robustness_extension_(false),
       context_lost_reason_(error::kUnknown),
       context_was_lost_(false),
       reset_by_robustness_extension_(false),
       supports_post_sub_buffer_(false),
       supports_commit_overlay_planes_(false),
       supports_async_swap_(false),
       context_type_(CONTEXT_TYPE_OPENGLES2),
       derivatives_explicitly_enabled_(false),
       frag_depth_explicitly_enabled_(false),
       draw_buffers_explicitly_enabled_(false),
       shader_texture_lod_explicitly_enabled_(false),
       compile_shader_always_succeeds_(false),
       lose_context_when_out_of_memory_(false),
+      should_use_native_gmb_for_backbuffer_(false),
       service_logging_(
           group_->gpu_preferences().enable_gpu_service_logging_gpu),
       viewport_max_width_(0),
       viewport_max_height_(0),
       texture_state_(group_->feature_info()->workarounds()),
       gpu_decoder_category_(TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(
           TRACE_DISABLED_BY_DEFAULT("gpu_decoder"))),
       gpu_trace_level_(2),
       gpu_trace_commands_(false),
       gpu_debug_commands_(false),
@@ skipping 45 matching lines @@
   if (feature_info_->workarounds().disable_timestamp_queries) {
     // Forcing time elapsed query for any GPU Timing Client forces it for all
     // clients in the context.
     GetGLContext()->CreateGPUTimingClient()->ForceTimeElapsedQuery();
   }
 
   // Save the loseContextWhenOutOfMemory context creation attribute.
   lose_context_when_out_of_memory_ =
       attrib_helper.lose_context_when_out_of_memory;
 
+  should_use_native_gmb_for_backbuffer_ =
+      attrib_helper.should_use_native_gmb_for_backbuffer;

[piman, 2016/06/27 19:37:37]

We need a check of some sort, somewhere. Right now an untrusted client on any
platform can request that, and we'll start trying to use
GL_TEXTURE_RECTANGLE_ARB (even if not present) and image_factory (even though it
could be NULL or not support CreateAnonymousImage).

[erikchen, 2016/06/27 22:16:04]

I added a check here. If should_use_native_gmb_for_backbuffer_ is true, then the
new logic checks that an image factory exists, and that the relevant texture
type is supported.

The implementation of BackTexture will handle an unimplemented
CreateAnonymousImage.

+
   // If the failIfMajorPerformanceCaveat context creation attribute was true
   // and we are using a software renderer, fail.
   if (attrib_helper.fail_if_major_perf_caveat &&
       feature_info_->feature_flags().is_swiftshader) {
     group_ = NULL;  // Must not destroy ContextGroup if it is not initialized.
     Destroy(true);
     return false;
   }
 
   if (!group_->Initialize(this, attrib_helper.context_type,
@@ skipping 98 matching lines @@
     state_.texture_units[tt].bound_texture_2d = ref;
     glBindTexture(GL_TEXTURE_2D, ref ? ref->service_id() : 0);
   }
   glActiveTexture(GL_TEXTURE0);
   CHECK_GL_ERROR();
 
   // cache ALPHA_BITS result for re-use with clear behaviour
   GLint alpha_bits = 0;
 
   if (offscreen) {
+    offscreen_buffer_should_have_alpha_ = attrib_helper.alpha_size > 0;
+
+    // Whether the offscreen buffer texture should have an alpha channel. Does
+    // not include logic from workarounds.
+    bool offscreen_buffer_texture_needs_alpha =
+        offscreen_buffer_should_have_alpha_ ||
+        (ChromiumImageNeedsRGBEmulation() &&
+         attrib_helper.should_use_native_gmb_for_backbuffer);
+
     if (attrib_helper.samples > 0 && attrib_helper.sample_buffers > 0 &&
         features().chromium_framebuffer_multisample) {
       // Per ext_framebuffer_multisample spec, need max bound on sample count.
       // max_sample_count must be initialized to a sane value.  If
       // glGetIntegerv() throws a GL error, it leaves its argument unchanged.
       GLint max_sample_count = 1;
       glGetIntegerv(GL_MAX_SAMPLES_EXT, &max_sample_count);
       offscreen_target_samples_ = std::min(attrib_helper.samples,
                                            max_sample_count);
     } else {
       offscreen_target_samples_ = 1;
     }
     offscreen_target_buffer_preserved_ = attrib_helper.buffer_preserved;
 
     if (gl::GetGLImplementation() == gl::kGLImplementationEGLGLES2) {
       const bool rgb8_supported =
           context_->HasExtension("GL_OES_rgb8_rgba8");
       // The only available default render buffer formats in GLES2 have very
       // little precision.  Don't enable multisampling unless 8-bit render
       // buffer formats are available--instead fall back to 8-bit textures.
       if (rgb8_supported && offscreen_target_samples_ > 1) {
-        offscreen_target_color_format_ = attrib_helper.alpha_size > 0 ?
-            GL_RGBA8 : GL_RGB8;
+        offscreen_target_color_format_ =
+            offscreen_buffer_texture_needs_alpha ? GL_RGBA8 : GL_RGB8;
       } else {
         offscreen_target_samples_ = 1;
         offscreen_target_color_format_ =
-            attrib_helper.alpha_size > 0 || workarounds().disable_gl_rgb_format
+            offscreen_buffer_texture_needs_alpha ||
+                    workarounds().disable_gl_rgb_format
                 ? GL_RGBA
                 : GL_RGB;
       }
 
       // ANGLE only supports packed depth/stencil formats, so use it if it is
       // available.
       const bool depth24_stencil8_supported =
           feature_info_->feature_flags().packed_depth24_stencil8;
       VLOG(1) << "GL_OES_packed_depth_stencil "
               << (depth24_stencil8_supported ? "" : "not ") << "supported.";
       if ((attrib_helper.depth_size > 0 || attrib_helper.stencil_size > 0) &&
           depth24_stencil8_supported) {
         offscreen_target_depth_format_ = GL_DEPTH24_STENCIL8;
         offscreen_target_stencil_format_ = 0;
       } else {
         // It may be the case that this depth/stencil combination is not
         // supported, but this will be checked later by CheckFramebufferStatus.
         offscreen_target_depth_format_ = attrib_helper.depth_size > 0 ?
             GL_DEPTH_COMPONENT16 : 0;
         offscreen_target_stencil_format_ = attrib_helper.stencil_size > 0 ?
             GL_STENCIL_INDEX8 : 0;
       }
     } else {
       offscreen_target_color_format_ =
-          attrib_helper.alpha_size > 0 || workarounds().disable_gl_rgb_format
+          offscreen_buffer_texture_needs_alpha ||
+                  workarounds().disable_gl_rgb_format
               ? GL_RGBA
               : GL_RGB;
 
       // If depth is requested at all, use the packed depth stencil format if
       // it's available, as some desktop GL drivers don't support any non-packed
       // formats for depth attachments.
       const bool depth24_stencil8_supported =
           feature_info_->feature_flags().packed_depth24_stencil8;
       VLOG(1) << "GL_EXT_packed_depth_stencil "
               << (depth24_stencil8_supported ? "" : "not ") << "supported.";
 
       if ((attrib_helper.depth_size > 0 || attrib_helper.stencil_size > 0) &&
           depth24_stencil8_supported) {
         offscreen_target_depth_format_ = GL_DEPTH24_STENCIL8;
         offscreen_target_stencil_format_ = 0;
       } else {
         offscreen_target_depth_format_ = attrib_helper.depth_size > 0 ?
             GL_DEPTH_COMPONENT : 0;
         offscreen_target_stencil_format_ = attrib_helper.stencil_size > 0 ?
             GL_STENCIL_INDEX : 0;
       }
     }
 
-    offscreen_saved_color_format_ =
-        attrib_helper.alpha_size > 0 || workarounds().disable_gl_rgb_format
-            ? GL_RGBA
-            : GL_RGB;
+    offscreen_saved_color_format_ = offscreen_buffer_texture_needs_alpha ||
+                                            workarounds().disable_gl_rgb_format
+                                        ? GL_RGBA
+                                        : GL_RGB;
 
     // Create the target frame buffer. This is the one that the client renders
     // directly to.
     offscreen_target_frame_buffer_.reset(new BackFramebuffer(this));
     offscreen_target_frame_buffer_->Create();
     // Due to GLES2 format limitations, either the color texture (for
     // non-multisampling) or the color render buffer (for multisampling) will be
     // attached to the offscreen frame buffer.  The render buffer has more
     // limited formats available to it, but the texture can't do multisampling.
     if (IsOffscreenBufferMultisampled()) {
-      offscreen_target_color_render_buffer_.reset(new BackRenderbuffer(
-          renderbuffer_manager(), memory_tracker(), &state_));
+      offscreen_target_color_render_buffer_.reset(new BackRenderbuffer(this));
       offscreen_target_color_render_buffer_->Create();
     } else {
       offscreen_target_color_texture_.reset(new BackTexture(this));
       offscreen_target_color_texture_->Create();
     }
-    offscreen_target_depth_render_buffer_.reset(new BackRenderbuffer(
-        renderbuffer_manager(), memory_tracker(), &state_));
+    offscreen_target_depth_render_buffer_.reset(new BackRenderbuffer(this));
     offscreen_target_depth_render_buffer_->Create();
-    offscreen_target_stencil_render_buffer_.reset(new BackRenderbuffer(
-        renderbuffer_manager(), memory_tracker(), &state_));
+    offscreen_target_stencil_render_buffer_.reset(new BackRenderbuffer(this));
     offscreen_target_stencil_render_buffer_->Create();
 
     // Create the saved offscreen texture. The target frame buffer is copied
     // here when SwapBuffers is called.
     offscreen_saved_frame_buffer_.reset(new BackFramebuffer(this));
     offscreen_saved_frame_buffer_->Create();
     //
     offscreen_saved_color_texture_.reset(new BackTexture(this));
     offscreen_saved_color_texture_->Create();
 
@@ skipping 292 matching lines @@
       feature_info_->feature_flags().oes_compressed_etc1_rgb8_texture;
   caps.texture_format_etc1_npot =
       caps.texture_format_etc1 && !workarounds().etc1_power_of_two_only;
   caps.texture_rectangle = feature_info_->feature_flags().arb_texture_rectangle;
   caps.texture_usage = feature_info_->feature_flags().angle_texture_usage;
   caps.texture_storage = feature_info_->feature_flags().ext_texture_storage;
   caps.discard_framebuffer =
       feature_info_->feature_flags().ext_discard_framebuffer;
   caps.sync_query = feature_info_->feature_flags().chromium_sync_query;
 
+  caps.chromium_image_rgb_emulation = ChromiumImageNeedsRGBEmulation();
 #if defined(OS_MACOSX)
   // This is unconditionally true on mac, no need to test for it at runtime.
   caps.iosurface = true;
-  caps.chromium_image_rgb_emulation = true;
 #endif
 
   caps.post_sub_buffer = supports_post_sub_buffer_;
   caps.commit_overlay_planes = supports_commit_overlay_planes_;
   caps.image = true;
   caps.surfaceless = surfaceless_;
   bool is_offscreen = !!offscreen_target_frame_buffer_.get();
   caps.flips_vertically = !is_offscreen && surface_->FlipsVertically();
   caps.msaa_is_slow = feature_info_->workarounds().msaa_is_slow;
 
@@ skipping 542 matching lines @@
 bool GLES2DecoderImpl::CheckFramebufferValid(
     Framebuffer* framebuffer,
     GLenum target,
     bool clear_uncleared_images,
     GLenum gl_error,
     const char* func_name) {
   if (!framebuffer) {
     if (surfaceless_)
       return false;
     if (backbuffer_needs_clear_bits_ && clear_uncleared_images) {
-      glClearColor(0, 0, 0, BackBufferHasAlpha() ? 0 : 1.f);
+      glClearColor(0, 0, 0, BackBufferAlphaClearColor());
       state_.SetDeviceColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
       glClearStencil(0);
       state_.SetDeviceStencilMaskSeparate(GL_FRONT, kDefaultStencilMask);
       state_.SetDeviceStencilMaskSeparate(GL_BACK, kDefaultStencilMask);
       glClearDepth(1.0f);
       state_.SetDeviceDepthMask(GL_TRUE);
       state_.SetDeviceCapabilityState(GL_SCISSOR_TEST, false);
       bool reset_draw_buffer = false;
       if ((backbuffer_needs_clear_bits_ & GL_COLOR_BUFFER_BIT) != 0 &&
           back_buffer_draw_buffer_ == GL_NONE) {
@@ skipping 646 matching lines @@
   if (w < 0 || h < 0 || h >= (INT_MAX / 4) / (w ? w : 1)) {
     LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
                << "to allocate storage due to excessive dimensions.";
     return false;
   }
 
   // Reallocate the offscreen target buffers.
   DCHECK(offscreen_target_color_format_);
   if (IsOffscreenBufferMultisampled()) {
     if (!offscreen_target_color_render_buffer_->AllocateStorage(
-            feature_info_.get(),
-            offscreen_size_,
-            offscreen_target_color_format_,
-            offscreen_target_samples_)) {
+            feature_info_.get(), offscreen_size_,
+            offscreen_target_color_format_, offscreen_target_samples_)) {
       LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
                  << "to allocate storage for offscreen target color buffer.";
       return false;
     }
   } else {
     if (!offscreen_target_color_texture_->AllocateStorage(
         offscreen_size_, offscreen_target_color_format_, false)) {
       LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
                  << "to allocate storage for offscreen target color texture.";
       return false;
@@ skipping 49 matching lines @@
   if (offscreen_target_frame_buffer_->CheckStatus() !=
       GL_FRAMEBUFFER_COMPLETE) {
       LOG(ERROR) << "GLES2DecoderImpl::ResizeOffscreenFrameBuffer failed "
                  << "because offscreen FBO was incomplete.";
     return false;
   }
 
   // Clear the target frame buffer.
   {
     ScopedFrameBufferBinder binder(this, offscreen_target_frame_buffer_->id());
-    glClearColor(0, 0, 0, BackBufferHasAlpha() ? 0 : 1.f);
+    glClearColor(0, 0, 0, BackBufferAlphaClearColor());
     state_.SetDeviceColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
     glClearStencil(0);
     state_.SetDeviceStencilMaskSeparate(GL_FRONT, kDefaultStencilMask);
     state_.SetDeviceStencilMaskSeparate(GL_BACK, kDefaultStencilMask);
     glClearDepth(0);
     state_.SetDeviceDepthMask(GL_TRUE);
     state_.SetDeviceCapabilityState(GL_SCISSOR_TEST, false);
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
     RestoreClearState();
   }
@@ skipping 362 matching lines @@
 }
 
 void GLES2DecoderImpl::DoBindBufferRange(GLenum target, GLuint index,
                                          GLuint client_id,
                                          GLintptr offset,
                                          GLsizeiptr size) {
   BindIndexedBufferImpl(target, index, client_id, offset, size,
                         kBindBufferRange, "glBindBufferRange");
 }
 
-bool GLES2DecoderImpl::BoundFramebufferHasColorAttachmentWithAlpha() {
+bool GLES2DecoderImpl::BoundFramebufferAllowsChangesToAlphaChannel() {
   Framebuffer* framebuffer =
       GetFramebufferInfoForTarget(GL_DRAW_FRAMEBUFFER_EXT);
   if (framebuffer)
     return framebuffer->HasAlphaMRT();
-  return BackBufferHasAlpha();
+  if (back_buffer_draw_buffer_ == GL_NONE)
+    return false;
+  if (offscreen_target_frame_buffer_.get()) {
+    GLenum format = offscreen_target_color_format_;
+    return (format == GL_RGBA || format == GL_RGBA8) &&
+           offscreen_buffer_should_have_alpha_;
+  }
+  return (back_buffer_color_format_ == GL_RGBA ||
+          back_buffer_color_format_ == GL_RGBA8);
 }
 
 bool GLES2DecoderImpl::BoundFramebufferHasDepthAttachment() {
   Framebuffer* framebuffer =
       GetFramebufferInfoForTarget(GL_DRAW_FRAMEBUFFER_EXT);
   if (framebuffer) {
     return framebuffer->HasDepthAttachment();
   }
   if (offscreen_target_frame_buffer_.get()) {
     return offscreen_target_depth_format_ != 0;
   }
   return back_buffer_has_depth_;
 }
 
 bool GLES2DecoderImpl::BoundFramebufferHasStencilAttachment() {
   Framebuffer* framebuffer =
       GetFramebufferInfoForTarget(GL_DRAW_FRAMEBUFFER_EXT);
   if (framebuffer) {
     return framebuffer->HasStencilAttachment();
   }
   if (offscreen_target_frame_buffer_.get()) {
     return offscreen_target_stencil_format_ != 0 ||
            offscreen_target_depth_format_ == GL_DEPTH24_STENCIL8;
   }
   return back_buffer_has_stencil_;
 }
 
 void GLES2DecoderImpl::ApplyDirtyState() {
   if (framebuffer_state_.clear_state_dirty) {
-    bool have_alpha = BoundFramebufferHasColorAttachmentWithAlpha();
-    state_.SetDeviceColorMask(state_.color_mask_red,
-                              state_.color_mask_green,
+    bool allows_alpha_change = BoundFramebufferAllowsChangesToAlphaChannel();
+    state_.SetDeviceColorMask(state_.color_mask_red, state_.color_mask_green,
                               state_.color_mask_blue,
-                              state_.color_mask_alpha && have_alpha);
+                              state_.color_mask_alpha && allows_alpha_change);
 
     bool have_depth = BoundFramebufferHasDepthAttachment();
     state_.SetDeviceDepthMask(state_.depth_mask && have_depth);
 
     bool have_stencil = BoundFramebufferHasStencilAttachment();
     state_.SetDeviceStencilMaskSeparate(
         GL_FRONT, have_stencil ? state_.stencil_front_writemask : 0);
     state_.SetDeviceStencilMaskSeparate(
         GL_BACK, have_stencil ? state_.stencil_back_writemask : 0);
 
@@ skipping 770 matching lines @@
               framebuffer->HasSameInternalFormatsMRT()) {
             if (feature_info_->gl_version_info().is_desktop_core_profile) {
               glGetFramebufferAttachmentParameterivEXT(
                   GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
                   GL_FRAMEBUFFER_ATTACHMENT_ALPHA_SIZE, &v);
             } else {
               glGetIntegerv(GL_ALPHA_BITS, &v);
             }
           }
         } else {
-          v = (BackBufferHasAlpha() ? 8 : 0);
+          v = (ClientExposedBackBufferHasAlpha() ? 8 : 0);
         }
         params[0] = v;
       }
       return true;
     case GL_DEPTH_BITS:
       *num_written = 1;
       if (params) {
         GLint v = 0;
         if (feature_info_->gl_version_info().is_desktop_core_profile) {
           Framebuffer* framebuffer =
@@ skipping 7340 matching lines @@
           MarkContextLost(error::kUnknown);
           group_->LoseContexts(error::kUnknown);
           return;
         }
 
         // Clear the offscreen color texture.
         // TODO(piman): Is this still necessary?
         {
           ScopedFrameBufferBinder binder(this,
                                          offscreen_saved_frame_buffer_->id());
-          glClearColor(0, 0, 0, 0);
+          glClearColor(0, 0, 0, BackBufferAlphaClearColor());
           state_.SetDeviceColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
           state_.SetDeviceCapabilityState(GL_SCISSOR_TEST, false);
           glClear(GL_COLOR_BUFFER_BIT);
           RestoreClearState();
         }
       }
     }
 
     if (offscreen_size_.width() == 0 || offscreen_size_.height() == 0)
       return;
@@ skipping 3464 matching lines @@
   // The workaround only works if the source texture consists of the channels
   // kRGB or kRGBA.
   if (channels_exist != GLES2Util::kRGBA && channels_exist != GLES2Util::kRGB)
     return false;
 
   *source_texture_target = texture->texture()->target();
   *source_texture_service_id = texture->service_id();
   return true;
 }
 
+bool GLES2DecoderImpl::ChromiumImageNeedsRGBEmulation() {
+#if defined(OS_MACOSX)

[piman, 2016/06/27 19:37:36]

nit: is this something maybe the ImageFactory could describe?

[erikchen, 2016/06/27 22:16:03]

Done.

+  return true;
+#else
+  return false;
+#endif
+}
+
 error::Error GLES2DecoderImpl::HandleBindFragmentInputLocationCHROMIUMBucket(
     uint32_t immediate_data_size,
     const void* cmd_data) {
   const gles2::cmds::BindFragmentInputLocationCHROMIUMBucket& c =
       *static_cast<const gles2::cmds::BindFragmentInputLocationCHROMIUMBucket*>(
           cmd_data);
   if (!features().chromium_path_rendering) {
     return error::kUnknownCommand;
   }
 
@@ skipping 143 matching lines @@
 }
 
 // Include the auto-generated part of this file. We split this because it means
 // we can easily edit the non-auto generated parts right here in this file
 // instead of having to edit some template or the code generator.
 #include "base/macros.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu