[Pixman] [PATCH 0/8] Add glyph API

[Søren Sandmann]

Hi,


The following patch series add a new API for caching and compositing
glyphs. Compositing entire strings of glyphs in one go is a
substantial reduction in overhead by itself, but the series also
contains a few optimizations that exploit glyph specific properties of
the compositing operations.

The API is centered around the concept of a glyph cache, which is
essentially a hash table that maps two keys (they are called "font"
and "glyph" in the API to suggest why there are two, but pixman
doesn't actually care what they represent) to an opaque pointer that
represents a stored glyph.

To composite a glyph string, an application is supposed to walk its
list of glyphs and look each one up in the cache. If it isn't there,
the application must produce a rasterization in the form of a pixman
image and insert it into the cache. Then, the opaque pointers returned
from the cache along with glyph positions, are passed back into pixman
for compositing.
    
While this is going on, the cache must be "frozen", which basically
means that glyphs will not be evicted from it. That way, the
application can be sure that all the glyphs are available at
compositing time. Afterwards, when the cache is "thawed", it may
decide to evict some glyphs if the cache is too full.

There are a few more details about the API in patch 2/8.

I'll post separate patches that port the X server and cairo over to
use this new API. These will contain performance results, but here is
a summary:

cairo:
        Speedups
             firefox-talos-gfx  5919.67 -> 4360.70:  1.36x speedup
             xfce4-terminal-a1  1600.87 -> 1264.19:  1.27x speedup
            gnome-terminal-vim  1925.08 -> 1788.56:  1.08x speedup
          firefox-planet-gnome  6906.81 -> 6480.79:  1.07x speedup
    
        Slowdowns
                poppler-reseau  370.01  -> 397.08:   1.07x slowdown

X server:
        Speedups:
            firefox-talos-gfx  13669.42 -> 3717.03:  3.68x speedup
             xfce4-terminal-a1  1842.63 -> 1086.13:  1.70x speedup
                     evolution  1401.95 -> 897.70:   1.56x speedup
            gnome-terminal-vim  1859.13 -> 1192.92:  1.56x speedup
                       poppler  1650.37 -> 1244.72:  1.33x speedup
          firefox-planet-gnome  7300.14 -> 5751.90:  1.27x speedup
                          gvim  1385.19 -> 1284.40:  1.08x speedup


Soren