Re: compositing

The work to be done is proportional to the "damaged" pixels on
the screen needing recompositing.  What is more, most of the pixels
are typically unity alpha, and don't need compositing; only the
areas near the "edges" will typically need work.

This typically will involve windows no more than a screen's worth
in a bad case, though I'm sure we can spend alot of time
generating pathological cases and have lots of fun :-).
The typical case is way less than this.

And current hardware does this sort of thing for breakfast.
It is one of the things that modern hardware is really good
at.

Some measurements of getting hardware acceleration for
alpha blended text showed a factor of 30 speedup over software,
and as things are even usable in the current software only
implementation, we're very comfortable with the design.
(even ignoring the existence proofs of other systems).
                            - Jim


On Wed, 2003-11-12 at 15:45, 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? 
> 
> 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?
> 
> =====
> Jon Smirl
> jonsmirl-/[email protected]
> 
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-- 
Jim Gettys <[email protected]>
HP Labs, Cambridge Research Laboratory