[cairo] src surface clip problems

Vladimir Vukicevic vladimirv at gmail.com
Thu Aug 17 14:53:55 PDT 2006

On 8/16/06, Carl Worth <cworth at cworth.org> wrote:
> On Tue, 8 Aug 2006 14:10:10 -0700, "Vladimir Vukicevic" wrote:
> >
> > (Note that the resulting image still isn't correct, due to broken
> > pixman upscaling -- in particular, the left and right edges should be
> > solid green, and not green-mixed-with-.. black? transparent black?
> > something.)
> Are you certain the image is incorrect? The source image has a sharp
> transition from green (0,1,0) to blue (0,0,1) from one pixel to the
> next.

Yep, I'm looking at the left and right edges of the image, not the
green-to-blue transition (which is correct).  pixman has all pixels
that are not contained within the image as transparent black; the
problem is that the sampling functions don't take into account image
edges at all, and instead read from the transparent black
out-of-bounds region even if they're not part of the compositing
operation.  Specifically, the leftmost and rightmost column of pixels
in that image sould be solid green, not (0.25,0.75,0.0).

    - Vlad

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