[Pixman] [RFC] dithering 16 bit gradients

Jeff Muizelaar jmuizelaar at mozilla.com
Wed Jul 11 09:54:46 PDT 2012

Here's a work in progress that adds dithering for 16 bit gradients. This does a 2x2 ordered dither in the same way that Skia does. Skia and Coregraphics also do dithering of 32bit gradients which I expect would also be useful for pixman in the future too.

This patch adds a partial implementation of a 16 bit pipeline in addition to the existing wide and narrow ones. This probably isn't strictly necessary, but is important for decent performance. The 16 bit pipeline is only used in the specific cases where it is supported, everything else is left unimplemented.

One of the things I'm currently unhappy with is that it duplicates the gradient walker code for 16 bits. We could turn it into a large macro that does the appropriate things for 16 bit and 32 bit versions, but that's not particularly appealing.

Does anyone have any other thoughts on this?


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