[cairo] Road to 1.10

[Owen Taylor]

On Mon, 2009-02-16 at 10:06 +0000, Chris Wilson wrote:

[...]

> On a more wider topic, having played with wayland and creating a
> cairo-based compositor, we sorely lack the ability to use a
> non-premultiplied source (such as an OpenGL window, or SDL surface as
> above). CAIRO_FORMAT_ARGB32_NON_PREMULTIPLIED_SOURCE - hideous, but
> fairly trivial to handle in a shader. (Slightly more work to add the
> extra code paths to pixman though!)

Hmmm, I don't know about SDL, but an OpenGL-rendered destination is
almost always going to be premultiplied - the math just doesn't work out
otherwise. (See the clutter bug report that I referenced inthe other
mail for more detai about compositing math.) A
"NON_PREMULTIPLIED_SOURCE" would be slightly useful for image data -
from GdkPixbuf or libpng, say, but premultiplication, even in the CPU,
is pretty much free if you already have to copy the data around or
reformat it.

- Owen