[cairo] JIT for pixman

[Freddie Witherden]

Hi all,

> > i am interested on working on a JIT for pixman compisiting code
> > (http://cairographics.org/summerofcode/ideas/). I have some very
> > (very...) early ideas on what can be done and how it should be done
> > using the llvm framework.
> 
> I consider a JIT compiler for pixman and multithreading in cairo and
> pixman the two most important long-term projects right now, so thanks
> for your interest in this.

I am unsure there; if only 10-25 different compositing formats are used,
on average then is the ability to specialise any arbitrary formats all
that useful? If 5% of the possible operators take up 80% of the time
then it is probably better to ensure that they are well optimised
instead.

I think that the functionality provided by JIT is better exploited when
dealing with per-pixel manipulation filters. (Of which compositing is a
subset.) Take a look at Apple's CoreImage kernels or GLSL pixel shaders.
Support for something like these in Cairo (user-definable per-pixel
filters) would benefit greatly from JIT.

I also agree that while LLVM is without doubt a heavyweight solution, it
is very well supported and well tested. (Apple I believe use it for
OpenGL shader emulation and I believe Gallium3D plan to do the same.)

So in short: JIT = neat; using it just for compositing = not so neat.

Regards, Freddie.
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