Delete background tab IOSurfaces on Mac.

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 82 matching lines @@
   UnrefIOSurface();
 }
 
 void CompositingIOSurfaceMac::SetIOSurface(uint64 io_surface_handle) {
   CGLSetCurrentContext(cglContext_);
   MapIOSurfaceToTexture(io_surface_handle);
   CGLSetCurrentContext(0);
 }
 
 void CompositingIOSurfaceMac::DrawIOSurface(NSView* view) {
-  TRACE_EVENT0("browser", "CompositingIOSurfaceMac::DrawIOSurface");
   CGLSetCurrentContext(cglContext_);
 
   bool has_io_surface = MapIOSurfaceToTexture(io_surface_handle_);
 
+  TRACE_EVENT1("browser", "CompositingIOSurfaceMac::DrawIOSurface",
+               "has_io_surface", has_io_surface);
+
   [glContext_ setView:view];
   NSSize window_size = [view frame].size;
   glViewport(0, 0, window_size.width, window_size.height);
 
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(0, window_size.width, window_size.height, 0, -1, 1);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
 
@@ skipping 16 matching lines @@
 
     // Draw the color channels from the incoming texture.
     glBindTexture(GL_TEXTURE_RECTANGLE_ARB, texture_); CHECK_GL_ERROR();
     glEnable(GL_TEXTURE_RECTANGLE_ARB); CHECK_GL_ERROR();
 
     DrawQuad(quad_);
 
     glBindTexture(GL_TEXTURE_RECTANGLE_ARB, 0); CHECK_GL_ERROR();
   }
 
   CGLFlushDrawable(cglContext_);

[vangelis, 2012/04/18 20:32:26]

Can we send the acknowledgement back to the GPU process before we call
CGLFlushDrawable() to avoid being descheduled while waiting for vsync?  The
windows port seems to do that.

[jbates, 2012/04/18 23:01:58]

The SwapBuffersAck is intentionally going back to the renderer after the native
SwapBuffers completes so that the renderer produces frames at a consistent 60hz
(or less if the GPU load is too high). If we send it back early, the start time
of the renderer's RAF will be inconsistent and I think that will make the
framerate janky. The renderer is already one frame ahead of the GPU process, so
sending the Ack back early would only be a work around for the GPU process
unscheduling logic. I think it would be better to implement a full solution to
allow the GPU process to make progress on gl commands that do not depend on the
IOSurface completing (as we discussed with Al).

 
   CGLSetCurrentContext(0);
 }
 
 bool CompositingIOSurfaceMac::CopyTo(const gfx::Size& dst_size, void* out) {
   if (!MapIOSurfaceToTexture(io_surface_handle_))
     return false;
 
   CGLSetCurrentContext(cglContext_);
   GLuint target = GL_TEXTURE_RECTANGLE_ARB;
@@ skipping 129 matching lines @@
   glDisableClientState(GL_TEXTURE_COORD_ARRAY);
 }
 
 void CompositingIOSurfaceMac::UnrefIOSurfaceWithContextCurrent() {
   if (texture_) {
     glDeleteTextures(1, &texture_);
     texture_ = 0;
   }
 
   io_surface_.reset();
+
+  // Forget the ID, because even if it is still around when we want to use it
+  // again, OSX may have reused the same ID for a new tab and we don't want to
+  // blit random tab contents.
+  io_surface_handle_ = 0;
 }
 
 void CompositingIOSurfaceMac::GlobalFrameDidChange() {
   [glContext_ update];
 }
 
 void CompositingIOSurfaceMac::ClearDrawable() {
   [glContext_ clearDrawable];
   UnrefIOSurface();
 }