RFC Proposal an X11 SYNC counter for each RANDR CRTC

[Dirk Thierbach]

On Sat, Mar 31, 2007 at 06:20:25PM +0200, Antony Lesuisse wrote:
> RANDR 1.2 brings the concept of differents CRTC displaying parts of the 
> root window. I think each CRTC should define an SYNC SystemCounters named 
> CRTC0_VSYNC, CRTC1_VSYNC. That counter would be incremented twice a frame:
> 
> 1 start of drawing frame 1
> 2 end of drawing frame 1, start of vblank
> 3 start of drawing frame 2
> 4 end of drawing frame 2, start of vblank
> etc...
> 
> or just once a frame by 2:
> 
> 2 end of drawing frame 1, start of vblank
> 4 end of drawing frame 2, start of vblank
> etc...
> 
> Jim Gettys explained that SYNC extension had been designed for that.

If X is at some time in the future going to support TV's properly, it
would be nice to have some information in a SYNC extension telling
which half-frame is currently displaying. The external TV encoder chips
all make this information available, and some applications could make
good use of this information.

I have to admit that I have never come across the concept of a
"SystemCounter" before, so another stupid question would be if those
counters have to be polled, or if an application could subscribe to
some sort of event which is received when the counter(s) change.

- Dirk