[cairo] Survey of polygon rasterization techniques

[David Turner]

> The thing that made a noticeable difference for us was adding a y
> coordinate  to the spans. This made it possible to generate more spans in one go (we 
> increased the FT_MAX_GRAY_SPANS from 32 to 256). It made a big difference
> for smaller polygons where function call overhead was actually dominating the 
> profile. 

Ah, nice trick, and good to know :-) 

I can understand why this would make such a difference for small polygons.
this function call over-head doesn't appear on my typical benchmarks, because
my inputs are glyph vectors which are generally more complex.

but for general-purpose graphics rendering, that's absolutely neat, bravo.

> I'm not sure whether that patch makes a lot of sense for
> FreeType  main, but if you're interested I could extract the patches and send them
> to you sometime this week.
> 
I think I can extract the changes myself easily. However, since the span interface
is part of the public FreeType API, I'm not going to change it :-(

that's still valuable information. Thanks !

- David