[Cairo] Text APIs round 2

[Carl Worth]

On Aug 15, Keith Packard wrote:
 > However, you can't get 'correct' output unless you provide an API that 
 > specifies the font for each glyph as the compositing will be broken when 
 > switching fonts.

Is the concern then for overlapping glyphs from separate fonts that
need to be pre-composited together? Is that commonly needed? Or is
there some other aspect of "correct" output I'm not thinking of?

I'm fine accepting the font-per-glyph API if there's a compelling need
for it. (The number of backend text requests generated seems an
optimization issue that could still be handled without requiring this
API).

In the absence of a compelling need, I would prefer not including the
font in the glyph structure --- that would seem a better fit for the
stateful nature of the rest of Cairo.

But my opinions are not too strong here. I'm no expert on text/fonts
and I'll gladly follow informed decisions from those who are.

-Carl