[cairo] Bug drawing PNG images with transparency

[Carl Worth]

On Fri, 04 Aug 2006 23:22:59 +0200, Franz Schmid wrote:
> Made some more tests with Scribus and other small test
> applications on that issue. It comes out that the
> image surface is responsible for the vanishing transparency,
> if i use the xlib backend everything works as expected.
...
> Drawing an image with transparent areas onto a cairo_image_surface
> fails with the transparency information lost in the following cases:
> 1) a cairo_scale operator != 1 is applied to the surface
> 2) the image is painted with cairo_paint_with_alpha with an alpha
>     value != 1, in this case the former transparent area has some
>     weired color shifts
> 3) a cairo_rotate operation is applied to the surface
> 4) a clipping paths is set

These details sound very, very similar to what Vladimir ran
into. Thanks to his help, we now have a test case for this in cairo
(source-clip-scale) along with a recently pushed fix:

http://gitweb.freedesktop.org/?p=cairo.git;a=commit;h=72e25648c4c4bc82ddd938aa4e05887a293f0d8b

If you could give the latest cairo a try and see if it fixes your
problem, then that would be great. (This fix will also be in the 1.2.4
release we plan to make today.)

-Carl
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