How do I wait for vertical retrace?

[Barry Scott]

Glynn Clements wrote:
> Carsten Haitzler (The Rasterman) wrote:
>
>   
>> wonderful... in theory. in practice a lot of hardware ONLY provides a vblank
>> interrupt. no interrupt for line X. :(
>>     
>
> You don't need the signal to come directly from the video hardware. If
> you know your clock frequencies, you can use the OS' timers; you just
> need to phase-lock to vsync to prevent drift.
>
>   
Without the signal from the hardware you cannot avoid tearing. We tried 
using
OS timer to get smooth animation and it does not work very well on 
Linux. Only
the DRI VBLANK method works.

Barry