Framebuffer clear() needs to consider the situation some draw buffers are disabled.

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 <vector>
 
 #include "base/basictypes.h"
@@ skipping 46 matching lines @@
     virtual ~Attachment() {}
   };
 
   Framebuffer(FramebufferManager* manager, GLuint service_id);
 
   GLuint service_id() const {
     return service_id_;
   }
 
   bool HasUnclearedAttachment(GLenum attachment) const;
+  bool HasUnclearedColorAttachments() const;
 
   void MarkAttachmentAsCleared(
     RenderbufferManager* renderbuffer_manager,
     TextureManager* texture_manager,
     GLenum attachment,
     bool cleared);
 
   // Attaches a renderbuffer to a particlar attachment.
   // Pass null to detach.
   void AttachRenderbuffer(
@@ skipping 45 matching lines @@
   // Implements optimized glGetFramebufferStatus.
   GLenum GetStatus(TextureManager* texture_manager, GLenum target) const;
 
   // Check all attachments are cleared
   bool IsCleared() const;
 
   GLenum GetDrawBuffer(GLenum draw_buffer) const;
 
   void SetDrawBuffers(GLsizei n, const GLenum* bufs);
 
+  // If a color buffer is attached to GL_COLOR_ATTACHMENTi, enable that
+  // draw buffer for glClear().
+  void PrepareDrawBuffersForClear() const;
+
+  // Recover draw buffers states that have been changed in
+  // PrepareDrawBuffersForClear().
+  void RecoverDrawBuffersAfterClear() const;

[Ken Russell (switch to Gerrit), 2014/06/05 20:00:40]

For consistency I suggest "Restore" instead of "Recover", here and throughout.

[Zhenyao Mo, 2014/06/05 21:27:49]

Done.

+
   // Return true if any draw buffers has an alpha channel.
   bool HasAlphaMRT() const;
 
   static void ClearFramebufferCompleteComboMap();
 
   static bool AllowFramebufferComboCompleteMapForTesting() {
     return allow_framebuffer_combo_complete_map_;
   }
 
   void OnTextureRefDetached(TextureRef* texture);
@@ skipping 14 matching lines @@
     bool cleared);
 
   void MarkAsComplete(unsigned state_id) {
     framebuffer_complete_state_count_id_ = state_id;
   }
 
   unsigned framebuffer_complete_state_count_id() const {
     return framebuffer_complete_state_count_id_;
   }
 
+  // Helper function for PrepareDrawBuffersForClear() and
+  // RecoverDrawBuffersAfterClear().
+  void ChangeDrawBuffersHelper(bool recover) const;
+
   // The managers that owns this.
   FramebufferManager* manager_;
 
   bool deleted_;
 
   // Service side framebuffer id.
   GLuint service_id_;
 
   // Whether this framebuffer has ever been bound.
   bool has_been_bound_;
@@ skipping 118 matching lines @@
   typedef std::vector<TextureDetachObserver*> TextureDetachObserverVector;
   TextureDetachObserverVector texture_detach_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(FramebufferManager);
 };
 
 }  // namespace gles2
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_SERVICE_FRAMEBUFFER_MANAGER_H_