[cairo] rotated characters does not keep baseline

[Bill Spitzak]

Behdad Esfahbod wrote:

>>    During some (unrelated directly) discussions on the list I have learned that
>>    the effect can be due to glyph cache, that stores only single image of a letter
>>    that is later reused.  This seems to be wrong in any (metrics-)unhinted mode
>>    (rotated or not).
> 
> True.  We don't have a plan to fix it right now.  Any ideas?

Cache renderings at subpixel positions. I would think a 4x4 grid of 
subpixel positions would be sufficient. Probably more important than for 
rotated text, this will allow non-integer escapement of characters which 
would greatly improve non-hinted horizontal text. I would think this may 
also be necessary to correctly compose glphs even when hinting is on.

Hinting will probably round all escapements to an integer, and probably 
should do this for rotated text as well, rounding the *larger* of the 
two to an integer and scaling the other one by the same factor. Then 
hinted slanted text would use fewer variations on the glyphs but (i 
hope) enough to make the line look straight.