[cairo] Projective transformations

[Christophe Dehais]

Hi !

Would it be difficult to make cairo_matrix hold a full 3x3 projective
transformation matrix instead of an affine transformation (2x3 matrix)
? Such transformations (also called homography) handle perspective
transformations and can simulate a kind of poor man's 3D.

In a GUI context, many elements are planar, and the transformation
between 2 (perspective) views of a plan is a homography. So having
that in cairo could allow creating widgets that presently would
require using OpenGL.

Thoughts ?

cheers,
Christophe