Fix for surfaceless implementation

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 <stdio.h>
 
 #include <algorithm>
 #include <list>
@@ skipping 2670 matching lines @@
 
   bool call_gl_clear = true;
 #if defined(OS_ANDROID)
   // Temporary workaround for Android WebView because this clear ignores the
   // clip and corrupts that external UI of the App. Not calling glClear is ok
   // because the system already clears the buffer before each draw. Proper
   // fix might be setting the scissor clip properly before initialize. See
   // crbug.com/259023 for details.
   call_gl_clear = surface_->GetHandle();
 #endif
-  if (call_gl_clear) {
+  // It is possible for us to not have a framebuffer at this point. If we don't
+  // then clearing will only generate an error.
+  if (call_gl_clear &&
+      glCheckFramebufferStatusEXT(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE) {

[piman, 2014/09/24 18:28:18]

So there's more to it than the clear, higher up we're asking the
alpha/depth/stencil bits (line 2621).
I'm not a big fan of asking GL if it thinks the framebuffer is complete. We know
whether we're surfaceless or not, we should pass the information through to here
(and that way we can also fail the operations that touch the framebuffer).

[achaulk, 2014/09/24 20:00:04]

The clear is the only operation that requires a complete framebuffer. However if
we need to have a stencil buffer setup earlier to pull out info, I'm not sure
how well this will work. We could try to bind the framebuffer early in
BindToClient, but I'm not sure if that's early enough to affect this

     // Clear the backbuffer.
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
   }
 
   supports_post_sub_buffer_ = surface->SupportsPostSubBuffer();
   if (feature_info_->workarounds()
           .disable_post_sub_buffers_for_onscreen_surfaces &&
       !surface->IsOffscreen())
     supports_post_sub_buffer_ = false;
 
@@ skipping 8573 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 "gpu/command_buffer/service/gles2_cmd_decoder_autogen.h"
 
 }  // namespace gles2
 }  // namespace gpu