[Command buffer] workaround the framebuffer completeness bug for Intel Mac

gpu/command_buffer/service/framebuffer_manager.h

 // 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.
 
 #ifndef GPU_COMMAND_BUFFER_SERVICE_FRAMEBUFFER_MANAGER_H_
 #define GPU_COMMAND_BUFFER_SERVICE_FRAMEBUFFER_MANAGER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 129 matching lines @@
   }
 
   void MarkAsValid() {
     has_been_bound_ = true;
   }
 
   bool IsValid() const {
     return has_been_bound_ && !IsDeleted();
   }
 
+  bool ReadBufferHasNoImage() const;
+  bool DrawBuffersHaveNoImage(GLsizei& num, GLenum* buf) const;

[Zhenyao Mo, 2016/11/14 19:42:24]

1) I think DrawBuffersHaveMissingImage is a better name.  Otherwise it's
confusing because it could be read as "no images are attached to any draw
buffers".

2) "&num": this is against chromium coding style.  Use GLsizei* num instead.

3) Why do we need num? I think we can just get rid of it.

[yunchao, 2016/11/15 16:21:59]

Agreed.
Done.
Mac Intel driver still think it is framebuffer incomplete if 1) we reset
COLOR_ATTACHMENTi to GL_NONE for readBuffer or drawBuffers those are missing
image, 2)After reset, there is not valid read/draw buffer(all of them are
GL_NONE after reset). 
As a result, use parameter num to record the valid drawbuffers number after
reset. Generate INVALID_OPERATION （read） or return directly (draw) in Chromium
if num is 0. Don't go to driver to check framebuffer status for this situation.

+  bool ColorBuffersHaveImage() const;
+
   bool HasColorAttachment(int index) const;
   bool HasDepthAttachment() const;
   bool HasStencilAttachment() const;
   GLenum GetDepthFormat() const;
   GLenum GetStencilFormat() const;
   GLenum GetDrawBufferInternalFormat() const;
   GLenum GetReadBufferInternalFormat() const;
   // If the color attachment is a texture, returns its type; otherwise,
   // returns 0.
   GLenum GetReadBufferTextureType() const;
@@ skipping 213 matching lines @@
 
   scoped_refptr<FramebufferCompletenessCache> framebuffer_combo_complete_cache_;
 
   DISALLOW_COPY_AND_ASSIGN(FramebufferManager);
 };
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_FRAMEBUFFER_MANAGER_H_