[cairo] GSoC/scan converting rasteriser update

[M Joonas Pihlaja]

Heya,

Another blog update[1].  I've got it passing the test suite now
using the reference scan converter, so next I'm plugging in the
faster versions.  After that I'll look into streamlining the
clipping & masking with spans, and also possibly compositing
spans with pixman directly.  I'm really trying to avoid going
inside pixman right now though, since I'd like to think that the
cairo_span_renderer_t interface makes optimising span compositing
a fairly independent thing from everything leading up to that.

Still, the current span renderer does do it in a particularly
bone headed way using *yet*another* temp. mask surface, so I
expect that'll show up high in the profiles.  Just that until now
I haven't really paid much attention to speed given that there
are lower hanging fruit left to pick. :)

Joonas

[1] http://people.freedesktop.org/~joonas/status-blog/