Order the GL overlays above windows if possible.

content/browser/renderer_host/compositing_iosurface_mac.mm

 // 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 "content/browser/renderer_host/compositing_iosurface_mac.h"
 
 #include <OpenGL/OpenGL.h>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 149 matching lines @@
   return kCVReturnSuccess;
 }
 
 CompositingIOSurfaceMac::CopyContext::CopyContext() {
   Reset();
 }
 
 CompositingIOSurfaceMac::CopyContext::~CopyContext() {
 }
 
-CompositingIOSurfaceMac* CompositingIOSurfaceMac::Create() {
+// static
+CompositingIOSurfaceMac* CompositingIOSurfaceMac::Create(SurfaceOrder order) {
   TRACE_EVENT0("browser", "CompositingIOSurfaceMac::Create");
   IOSurfaceSupport* io_surface_support = IOSurfaceSupport::Initialize();
   if (!io_surface_support) {
     LOG(WARNING) << "No IOSurface support";
     return NULL;
   }
 
   std::vector<NSOpenGLPixelFormatAttribute> attributes;
   attributes.push_back(NSOpenGLPFADoubleBuffer);
   // We don't need a depth buffer - try setting its size to 0...
@@ skipping 10 matching lines @@
   }
 
   scoped_nsobject<NSOpenGLContext> glContext(
       [[NSOpenGLContext alloc] initWithFormat:glPixelFormat
                                  shareContext:nil]);
   if (!glContext) {
     LOG(ERROR) << "NSOpenGLContext initWithFormat failed";
     return NULL;
   }
 
-  // We "punch a hole" in the window, and have the WindowServer render the
-  // OpenGL surface underneath so we can draw over it.
-  GLint belowWindow = -1;
-  [glContext setValues:&belowWindow forParameter:NSOpenGLCPSurfaceOrder];
+  // If requested, ask the WindowServer to render the OpenGL surface underneath
+  // the window. This, combined with a hole punched in the window, will allow
+  // for views to "overlap" the GL surface from the user's point of view.
+  if (order == SURFACE_ORDER_BELOW_WINDOW) {
+    GLint belowWindow = -1;
+    [glContext setValues:&belowWindow forParameter:NSOpenGLCPSurfaceOrder];
+  }
 
   CGLContextObj cglContext = (CGLContextObj)[glContext CGLContextObj];
   if (!cglContext) {
     LOG(ERROR) << "CGLContextObj failed";
     return NULL;
   }
 
   // Draw at beam vsync.
   bool is_vsync_disabled =
       CommandLine::ForCurrentProcess()->HasSwitch(switches::kDisableGpuVsync);
@@ skipping 655 matching lines @@
   glDeleteFramebuffersEXT(1, &copy_context_.frame_buffer); CHECK_GL_ERROR();
   glDeleteTextures(1, &copy_context_.frame_buffer_texture); CHECK_GL_ERROR();
   glDeleteBuffers(1, &copy_context_.pixel_buffer); CHECK_GL_ERROR();
   if (copy_context_.use_fence) {
     glDeleteFencesAPPLE(1, &copy_context_.fence); CHECK_GL_ERROR();
   }
   copy_context_.Reset();
 }
 
 }  // namespace content