[PATCH 21/27] glamor: Improve the performance of PushPixels by, well, pushing pixels.

[Eric Anholt]

Markus Wick <markus at selfnet.de> writes:

> I didn't find any issues in this patch, but I don't see the point:
> Do we really want to convert a pixmap with 1 bit per pixel into a list 
> of enabled pixels on cpu?
> Isn't it as easy to upload this pixmap as texture and do everything else 
> in the pixel shader?
> In this way, we won't have to care about the location of the bitmap.

It's a good question.  My policy on performance improvements is: if it
is already written and it improves things, do it.  If there's more
improvement available still, somebody can come by with a patch later
showing even more win.

In particular, the concern I have with the way you propose is that
uploading temporary textures is expensive (and more expensive than it
ought to be on Intel -- which I've been trying to fix in parallel with
the glamor work).

Even with just the rendering idea in this patch, doing the transforms on
the GPU would probably be a significant win over what's here.  I'm
hoping once we land keithp's stuff we can reuse some helpers he wrote (I
think) to clean up a bunch of the core rendering paths.
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