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Call glFinish() before manually waiting for VBLANK

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If we manually wait for the VBLANK with:

  - SGI_video_sync
  - Direct usage of the DRM ioctl

Then we should call glFinish() first, or otherwise the swap-buffers
may be delayed by pending drawing and cause a tear.

http://bugzilla.openedhand.com/show_bug.cgi?id=1636

Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>
This commit is contained in:
Owen W. Taylor 2009-06-06 15:47:57 -04:00 committed by Emmanuele Bassi
parent b08bbcccad
commit 5425a6e311
1 changed files with 27 additions and 4 deletions
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27
clutter/glx/clutter-backend-glx.c
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@ -637,26 +637,48 @@ _clutter_backend_impl_get_type (void)
void
clutter_backend_glx_wait_for_vblank (ClutterBackendGLX *backend_glx)
{
/* If we are going to wait for VBLANK manually, we not only need
* to flush out pending drawing to the GPU before we sleep, we
* need to wait for it to finish. Otherwise, we may end up with
* the situation:
*
* - We finish drawing - GPU drawing continues
* - We go to sleep - GPU drawing continues
* VBLANK - We call glXSwapBuffers - GPU drawing continues
* - GPU drawing continues
* - Swap buffers happens
*
* Producing a tear. Calling glFinish() first will cause us to properly
* wait for the next VBLANK before we swap. This obviously does not
* happen when we use GLX_SWAP and let the driver do the right thing
*/
switch (backend_glx->vblank_type)
{
case CLUTTER_VBLANK_GLX_SWAP:
{
/* Nothing */
break;
}
case CLUTTER_VBLANK_GLX:
{
unsigned int retraceCount;
glFinish ();
backend_glx->get_video_sync (&retraceCount);
backend_glx->wait_video_sync (2,
(retraceCount + 1) % 2,
&retraceCount);
}
break;
case CLUTTER_VBLANK_DRI:
#ifdef __linux__
{
drm_wait_vblank_t blank;
glFinish ();
blank.request.type = DRM_VBLANK_RELATIVE;
blank.request.sequence = 1;
blank.request.signal = 0;
@ -664,6 +686,7 @@ clutter_backend_glx_wait_for_vblank (ClutterBackendGLX *backend_glx)
}
#endif
break;
case CLUTTER_VBLANK_NONE:
default:
break;