Re: compositing

Around 12 o'clock on Nov 12, Jon Smirl wrote:

> On decent hardware how fast is it to composite a screen? Can you do it once
> every refresh and still have enough time left over for a decent amount of
> drawing? 

I think so, but I don't have any accelerated servers to try it with.  
Certainly the software is at least a factor of 2 to 4 slower than the refresh 
rate, and sometimes a lot slower than that.

My guess is that the compositing will have almost no impact on a real GPU 
though.  We're talking about compositing perhaps a dozen 1/2MPel images, 
something even a several year old video card should do in it's sleep.

> For example let's say the window area was five times the screen area at
> 1280x1024 with a 70Htz refresh. That means you need to draw every 14ms. Does
> compositing take 1ms or 10ms of the refresh interval?

Two answers -- first, you won't put bits onto the screen that you don't 
need to, so any final compositing step is strictly limited to the actual 
screen size, and clipped so that areas occluded by opaque windows aren't 
copied at all. 

Second, I'm thinking of allowing the compositing manager to tell the
server not to bother saving bits of the window beyond the root window; in
that case, you'd not even be drawing the original image to the occluded
areas.

-keith