Ensure alpha channel in backbuffer is correct with DirectComposition.

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 1961 matching lines @@
   // TODO(zmo): when ES3 APIs are exposed to Nacl, make sure read_buffer_
   // setting is set correctly when SwapBuffers().
   GLenum back_buffer_read_buffer_;
   GLenum back_buffer_draw_buffer_;
 
   bool surfaceless_;
 
   // Backbuffer attachments that are currently undefined.
   uint32_t backbuffer_needs_clear_bits_;
 
+  uint64_t swaps_since_resize_;
+
   // The current decoder error communicates the decoder error through command
   // processing functions that do not return the error value. Should be set only
   // if not returning an error.
   error::Error current_decoder_error_;
 
   scoped_refptr<ShaderTranslatorInterface> vertex_translator_;
   scoped_refptr<ShaderTranslatorInterface> fragment_translator_;
 
   DisallowedFeatures disallowed_features_;
 
@@ skipping 525 matching lines @@
       offscreen_target_samples_(0),
       offscreen_target_buffer_preserved_(true),
       offscreen_saved_color_format_(0),
       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),
@@ skipping 1098 matching lines @@
   OnFboChanged();
 }
 
 bool GLES2DecoderImpl::CheckFramebufferValid(
     Framebuffer* framebuffer,
     GLenum target, const char* func_name) {
   if (!framebuffer) {
     if (surfaceless_)
       return false;
     if (backbuffer_needs_clear_bits_) {
-      glClearColor(0, 0, 0, (GLES2Util::GetChannelsForFormat(
-          offscreen_target_color_format_) & 0x0008) != 0 ? 0 : 1.f);
+      glClearColor(0, 0, 0, BackBufferHasAlpha() ? 0 : 1.f);
       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 674 matching lines @@
                           !!has_alpha)) {
       LOG(ERROR) << "GLES2DecoderImpl: Context lost because resize failed.";
       return error::kLostContext;
     }
     DCHECK(context_->IsCurrent(surface_.get()));
     if (!context_->IsCurrent(surface_.get())) {
       LOG(ERROR) << "GLES2DecoderImpl: Context lost because context no longer "
                  << "current after resize callback.";
       return error::kLostContext;
     }
+    if (surface_->BuffersFlipped()) {
+      backbuffer_needs_clear_bits_ |= GL_COLOR_BUFFER_BIT;
+    }
   }
 
+  swaps_since_resize_ = 0;
+
   return error::kNoError;
 }
 
 const char* GLES2DecoderImpl::GetCommandName(unsigned int command_id) const {
   if (command_id > kStartPoint && command_id < kNumCommands) {
     return gles2::GetCommandName(static_cast<CommandId>(command_id));
   }
   return GetCommonCommandName(static_cast<cmd::CommandId>(command_id));
 }
 
@@ skipping 7833 matching lines @@
 }
 
 void GLES2DecoderImpl::FinishSwapBuffers(gfx::SwapResult result) {
   if (result == gfx::SwapResult::SWAP_FAILED) {
     LOG(ERROR) << "Context lost because SwapBuffers failed.";
     if (!CheckResetStatus()) {
       MarkContextLost(error::kUnknown);
       group_->LoseContexts(error::kUnknown);
     }
   }
+  ++swaps_since_resize_;
+  if (swaps_since_resize_ == 1 && surface_->BuffersFlipped()) {
+    // The second buffer after a resize is new and needs to be cleared to
+    // known values.
+    backbuffer_needs_clear_bits_ |= GL_COLOR_BUFFER_BIT;
+  }
 }
 
 void GLES2DecoderImpl::DoCommitOverlayPlanes() {
   TRACE_EVENT0("gpu", "GLES2DecoderImpl::DoCommitOverlayPlanes");
   if (supports_async_swap_) {
     surface_->CommitOverlayPlanesAsync(base::Bind(
         &GLES2DecoderImpl::FinishSwapBuffers, base::AsWeakPtr(this)));
   } else {
     FinishSwapBuffers(surface_->CommitOverlayPlanes());
   }
@@ skipping 3349 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