[Command buffer]: Don't blit color buffer if draw buffers have no image during blitting

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 7992 matching lines @@
                          "invalid filter for integer format");
       return;
     }
 
     GLenum src_sized_format =
         GLES2Util::ConvertToSizedFormat(src_internal_format, src_type);
     DCHECK(read_framebuffer || (is_feedback_loop != FeedbackLoopUnknown));
     const Framebuffer::Attachment* read_buffer =
         is_feedback_loop == FeedbackLoopUnknown ?
         read_framebuffer->GetReadBufferAttachment() : nullptr;
+    bool draw_buffer_has_image = false;
     for (uint32_t ii = 0; ii < group_->max_draw_buffers(); ++ii) {
       GLenum dst_format = GetBoundColorDrawBufferInternalFormat(
           static_cast<GLint>(ii));
       GLenum dst_type = GetBoundColorDrawBufferType(static_cast<GLint>(ii));
       if (dst_format == 0)
         continue;
+      draw_buffer_has_image = true;
       if (!src_internal_format) {
         read_framebuffer_miss_image = true;
       }
       if (GetColorEncodingFromInternalFormat(dst_format) == GL_SRGB)
         draw_buffers_has_srgb = true;
       if (read_buffer_samples > 0 &&
           (src_sized_format !=
            GLES2Util::ConvertToSizedFormat(dst_format, dst_type))) {
         LOCAL_SET_GL_ERROR(GL_INVALID_OPERATION, func_name,
                            "src and dst formats differ for color");
@@ skipping 16 matching lines @@
             draw_framebuffer->GetAttachment(attachment);
         if (!draw_buffer || !read_buffer) {
           continue;
         }
         if (draw_buffer->IsSameAttachment(read_buffer)) {
           is_feedback_loop = FeedbackLoopTrue;
           break;
         }
       }
     }
+    if (draw_framebuffer && !draw_buffer_has_image)

[Zhenyao Mo, 2016/12/16 23:50:31]

You can't return early here.  DEPTH and STENCIL might have images and the mask
might have these bits also.

[yunchao, 2016/12/19 03:20:08]

You are correct. I made a mistake here. The code has been updated accordingly,
please take another look, Zhenyao. 

+      return;
   }
   if (is_feedback_loop == FeedbackLoopTrue) {
     LOCAL_SET_GL_ERROR(GL_INVALID_OPERATION, func_name,
         "source buffer and destination buffers are identical");
     return;
   }
   if (read_framebuffer_miss_image == true) {
     LOCAL_SET_GL_ERROR(GL_INVALID_OPERATION, func_name,
        "The designated attachment point(s) in read framebuffer miss image");
     return;
@@ skipping 10938 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