[SDL] Re: extension for 2D with DRI

Mattias Engdegård f91-men at nada.kth.se
Fri Apr 14 07:27:19 PDT 2000

>The beginning of your answer (sleeping for the inter-frame delay) is
>okay with me, but why poll for vertical retrace? As soon as the
>inter-frame delay is finish, fire off a blit command to the video
>accelerator (with the "wait for vretrace flag" enabled) and start
>preparing the next frame right away!

You are perfectly right; I must have been thinking of two things at the
same time, thus overtaxing the sponge pretending to be my brain.
I was concerned about synching for replaying at a fixed video/frame ratio,
but thinking about it, it is probably not very important since the vertical
refresh (~80Hz) is far higher than for movies movies (24 frames/s). So
I guess there is little risk of temporal aliasing artifacts from that,
and it's better to used fixed timing between frames.

I wonder if it makes sense to simulate the 50 interlaced half-frames
per second for TV playback, though. How do people do it? Simply pair them
together and run them at 25Hz?

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