Force GPU switch with CGLSetVirtualScreen only for compositor

ui/gl/gl_context_cgl.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 "ui/gl/gl_context_cgl.h"
 
 #include <OpenGL/CGLRenderers.h>
 #include <OpenGL/CGLTypes.h>
 #include <vector>
 
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface_cgl.h"
 #include "ui/gl/gpu_switching_manager.h"
 
 namespace gfx {
 
 bool g_support_renderer_switching;
 
+bool g_force_cgl_set_virtual_screen = false;
+
 static CGLPixelFormatObj GetPixelFormat() {
   static CGLPixelFormatObj format;
   if (format)
     return format;
   std::vector<CGLPixelFormatAttribute> attribs;
   // If the system supports dual gpus then allow offline renderers for every
   // context, so that they can all be in the same share group.
   if (ui::GpuSwitchingManager::GetInstance()->SupportsDualGpus()) {
     attribs.push_back(kCGLPFAAllowOfflineRenderers);
     g_support_renderer_switching = true;
@@ skipping 110 matching lines @@
       return false;
 
     for (int i = 0; i < virtual_screen_count; ++i) {
       int screen_renderer_id;
       if (CGLDescribePixelFormat(format, i, kCGLPFARendererID,
                                  &screen_renderer_id) != kCGLNoError)
         return false;
 
       screen_renderer_id &= kCGLRendererIDMatchingMask;
       if (screen_renderer_id == renderer_id) {
-        CGLSetVirtualScreen(static_cast<CGLContextObj>(context_), i);
+        // This call can hang on some AMD drivers
+        // http://crbug.com/227228
+        if (g_force_cgl_set_virtual_screen)

[jbauman, 2013/04/06 01:52:02]

I'd recommend moving this check up to the beginning of the block (next to
g_support_renderer_switching), to avoid doing unnecessary
CGLDescribePixelFormats if it's disabled.

[ccameron, 2013/04/08 17:25:14]

I put the whole thing in an if-block. My initial inclination was to maintain
valid values for screen_ and renderer_id_ in case they were used elsewhere, but
this is indeed the only place where they are used.

+          CGLSetVirtualScreen(static_cast<CGLContextObj>(context_), i);
         screen_ = i;
         break;
       }
     }
     renderer_id_ = renderer_id;
   }
 
   if (IsCurrent(surface))
     return true;
 
@@ skipping 97 matching lines @@
                             kCGLRPVideoMemory,
                             &video_memory) != kCGLNoError)
         continue;
     *bytes = video_memory;
     return true;
   }
 
   return false;
 }
 
+// static
+void GLContextCGL::ForceCGLSetVirtualScreen() {
+  g_force_cgl_set_virtual_screen = true;
+}
+
 GLContextCGL::~GLContextCGL() {
   Destroy();
 }
 
 GpuPreference GLContextCGL::GetGpuPreference() {
   return gpu_preference_;
 }
 
 void ScopedCGLDestroyRendererInfo::operator()(CGLRendererInfoObj x) const {
   CGLDestroyRendererInfo(x);
 }
 
 }  // namespace gfx