[Cairo] Color transforms

[Carl Worth]

On Jul 18, Owen Taylor wrote:
 > Just remember that any Cairo text API's for applications will be 
 > more or less "toy"; for heavy-duty usage, you need a Pango equivalent.
 > So, there is no point in getting too fancy with the part that
 > isn't "draw these glyphs at these positions".

Precisely. And we do not want anything resembling a Pango equivalent
sneaking into Cairo. So, not too worry, the API will not go beyond
glyph placement, (with transformation of course).

Cairo will also build on top of significant libraries such as freetype
and fontconfig.

So there's not a whole lot left for Cairo to have to do, (running a
few coordinates through a matrix is trivial enough). But as a
middleman, Cairo must be careful not to get in the way. A higher-level
"Pango equivalent" needs access to the metrics, etc. from the
lower-level libraries. Providing that access in a clean and portable
way may be the trickiest part of the interface to get right.

-Carl