[Pixman] About 2.5D effect

[Maarten Bosmans]

2011/10/12 唐博 <hitiger.2008 at yahoo.com.cn>:
> How can pixman achieve 2.5D effect, it's affine matirx is 3*3. If add Z axis coordinate, I found that it should apply 4*4 matrix.

Please lookup the three threads about projective transformations in
the list archives of august 2010.
No need to do the whole discussion again.

In short: while the most general case of 3D affine transformations
requires a 4x4 matrix for 3D homogeneous coordinates, if only affine
transformation in 2D + projective transformations are required, a 3x3
matrix suffices, which pixman has, in contrast to cairo, which only
uses the 2x3 upper elements of the matrix.

Maarten

> Who can tell me , thanks very much.
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