[Pixman] [patch] Gradient dithering into pixman

[Marc Jeanmougin]

Hi,

I'm Marc, I'm an Inkscape contributor, and I would like to improve
pixman by providing a patch to allow gradient dithering, to eliminate
all gradient banding. This "banding" problem is hugely visible in many
Inkscape files, and I hope you could help me putting it into pixman,
then in exposing the functionality into cairo.

I tried to very closely follow the existing code style, and I came up
with the proof of concept (attached Proof_of_concept.patch ), which
applies to pixman/master to enable the feature directly.

Since Inkscape also uses pixman to render files when exporting to png,
and that kind of dithering affects very significantly the file size (PNG
compression algorithm and randomness don't mix well) we also need a
switch to enable/disable it "at will".

I tried to understand how it could be done by looking at
pixman_image_set_* functions and finally came up with the other patch
attached 0001-Adds-a-gradient-dithering-function-to-pixman.patch (which
cannot directly be tested, since it would require changes in cairo to
call pixman_image_set_dithering, but changing "gradient->dithering =
PIXMAN_DITHERING_NONE;" to _BEST in pixman-image.c works)

Thanks for any help in merging this, or any pointer to how to improve it,

-- 
Marc
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