[cairo] Floating point API in Pixman

[Krzysztof Kosiński]

Hello

There are several bugs in the Cairo port of Inkscape that are caused
by the 16.16 fixed point coordinate format in Pixman. We can't switch
to Cairo until this is resolved, mainly because Inkscape is used to
render OpenStreetMap tiles and must be able to cope with very large
images - so in addition to supersampling, I would like to work on
floating point API in Pixman.

I note that there are some functions in pixman.h that start with
pixman_f_ and operate on floating point matrices. However, they appear
unused at the moment.

What is the best approach to introduce floating point-based API?
Should I add a new function starting with pixman_f_ for each Pixman
call that accepts fixed point coordinates? What about matrices that
are part of other data types, such as pixman_image_t - should there be
a compile time flag that selects which type of matrix is used?

Regards, Krzysztof