Add a transform feedback workaround for Intel GPUs on MacOSX

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 5695 matching lines @@
 }
 
 void GLES2DecoderImpl::DoResumeTransformFeedback() {
   DCHECK(state_.bound_transform_feedback.get());
   if (!state_.bound_transform_feedback->active() ||
       !state_.bound_transform_feedback->paused()) {
     LOCAL_SET_GL_ERROR(GL_INVALID_OPERATION, "glResumeTransformFeedback",
                        "transform feedback is not active or not paused");
     return;
   }
+  if (feature_info_->workarounds().use_transform_feedback_temp_unbind) {
+    glBindTransformFeedback(GL_TRANSFORM_FEEDBACK, 0);
+    state_.bound_transform_feedback->DoBindTransformFeedback(

[Zhenyao Mo, 2016/08/18 17:39:31]

I think you should just do glBindTransformFeedback(GL_TRANSFORM_FEEDBACK,
state_.bound_transform_feedback->service_id()) here to avoid all the unnecessary
steps.

[Zhenyao Mo, 2016/08/18 18:49:05]

1) I am still worried that this is caused by Chrome command buffer, so can you
do a glGetIntegerv(GL_TRANSFORM_FEEDBACK_BINDING) and see if the ID is lost? If
not, 2)

2) Do we have to Bind to 0 first then the currently bound transformfeedback?  If
we just bind it, will that work around the issue?

[Ken Russell (switch to Gerrit), 2016/08/19 00:13:35]

I think this is very likely a driver bug. These tests pass on my MacBook Pro
Retina with NVIDIA GPU.

[jchen10, 2016/08/19 01:01:23]

Anyway the worry makes sense to me. I have tried them. It turned out that 
    ID queried from GL_TRANSFORM_FEEDBACK_BINDING was same as
state_.bound_transform_feedback->service_id(), and
    the walk around didn't work without binding to 0 first.
So I think it's more likely a driver bug.

+        GL_TRANSFORM_FEEDBACK);
+  }
   state_.bound_transform_feedback->DoResumeTransformFeedback();
 }
 
 void GLES2DecoderImpl::DoDisableVertexAttribArray(GLuint index) {
   if (state_.vertex_attrib_manager->Enable(index, false)) {
     if (index != 0 || gl_version_info().BehavesLikeGLES()) {
       glDisableVertexAttribArray(index);
     }
   } else {
     LOCAL_SET_GL_ERROR(
@@ skipping 12054 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