Syncing on every other vblank

brasse · 11-02-06, 03:57 AM

Hello!

I have question for you regarding vblank syncing. I know that if I set the environment variable __GL_SYNC_TO_VBLANK to non-zero value I get my application to sync to the vblank when I go glXSwapBuffers(). Now what I want to do is sync to every other vblank (if the vblank is 60 Hz, I want my application to run at 30 FPS).

Initially I thought that this would be easy. My guess was that if I call glXSwapBuffers() with an interval of more that 1000/60 ms I would get an FPS of 30. This seemed reasonable since I get a FPS of 60 if I call glXSwapBuffers() with an interval less than 1000/60 ms. However, for my particular application I get an FPS around 43 (the time it takes to draw all my stuff is ~23 ms).

Does anyone here know if there is a way to make the driver always sync to the next vblank, even if my call to glXSwapBuffers() comes a bit late?

Regards,
Mattias

lcs · 11-02-06, 09:36 AM

GLX_SGI_swap_control or perhaps GLX_SGI_video_sync?

**AaronP** · 11-02-06, 11:56 AM

Try __GL_SYNC_TO_VBLANK=2

brasse · 11-03-06, 02:47 AM

Thanks. Setting __GL_SYNC_TO_VBLANK=2 works perfectly! I haven't seen it documented anywhere, but it works! :-)

:.:: mattias

11-02-06, 03:57 AM	#1
brasse Registered User Join Date: Nov 2006 Posts: 2	Syncing on every other vblank Hello! I have question for you regarding vblank syncing. I know that if I set the environment variable __GL_SYNC_TO_VBLANK to non-zero value I get my application to sync to the vblank when I go glXSwapBuffers(). Now what I want to do is sync to every other vblank (if the vblank is 60 Hz, I want my application to run at 30 FPS). Initially I thought that this would be easy. My guess was that if I call glXSwapBuffers() with an interval of more that 1000/60 ms I would get an FPS of 30. This seemed reasonable since I get a FPS of 60 if I call glXSwapBuffers() with an interval less than 1000/60 ms. However, for my particular application I get an FPS around 43 (the time it takes to draw all my stuff is ~23 ms). Does anyone here know if there is a way to make the driver always sync to the next vblank, even if my call to glXSwapBuffers() comes a bit late? Regards, Mattias

11-02-06, 09:36 AM	#2
lcs Registered User Join Date: Aug 2003 Posts: 14	Re: Syncing on every other vblank GLX_SGI_swap_control or perhaps GLX_SGI_video_sync?

11-02-06, 11:56 AM	#3
AaronP NVIDIA Corporation Join Date: Mar 2005 Posts: 2,487	Re: Syncing on every other vblank Try __GL_SYNC_TO_VBLANK=2

11-03-06, 02:47 AM	#4
brasse Registered User Join Date: Nov 2006 Posts: 2	Re: Syncing on every other vblank Thanks. Setting __GL_SYNC_TO_VBLANK=2 works perfectly! I haven't seen it documented anywhere, but it works! :-) :.:: mattias