render improvements

[Owen Taylor]

On Tue, 2005-04-19 at 09:23 +0200, Lars Knoll wrote:

> We know that the biggest performance bottleneck currently is the framebuffer 
> access, so I think that's the place we should focus currently. Using MMX 
> instructions to fetch/store a scanline from the framebuffer is a good start, 
> but in the long term we need DMA if we want to get any reasonable 
> performance.
> 
> We can try a patch based aproach later on once we found a way to get fast 
> access to the framebuffer data. As long as this is not solved it IMO doesn't 
> make a whole lot of sense to try to improve the implementation in this 
> respect.

Possibly the most efficient thing to do is to simple, whenever you need
to read data back from a pixmap in the framebuffer for a composite
operation, is to simply kick the pixmap *out* of the framebuffer 
permanently.

More sophisticated pixmap migration schemes, including in some cases
keeping two copies of the pixmap might make sense too, but reading
back from the framebuffer is expensive enough that a 
one-strike-and-your-out approach might be good enough.

Regards,
						Owen

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