[cairo] Cairo 1.10 rendering text to transparent image surface [BUG?]

Geoff Youngs g.youngs at livelinktechnology.net
Tue Nov 30 09:07:45 PST 2010


I've tried using the latest versions of pixman & cairo from git and
I'm still getting colour corruption at the edge of glyphs rendered to
an image surface with a non-opaque background...

If I manually disable CPU optimizations, and patch
fast_composite_over_n_8888_8888_ca in pixman-fast-patch.c so that it
only uses the mask alpha channel (instead of using all the channels
from the mask), then I don't get the colour corruption anymore - but
I've got no idea what kind of impact this has on other operations?

Can anyone else confirm this behaviour?  Or point out what I'm doing wrong?

Thanks in advance,


On 26 November 2010 16:32, Geoff Youngs <g.youngs at livelinktechnology.net> wrote:
> Hi,
> I've found that rendering light coloured (it's not so visible with
> black) text to an image surface with an (at least partially)
> transparent background results in unwanted artefacts where I'd expect
> to see smooth anti-aliasing.
> Example code was compiled with:
> gcc `pkg-config --cflags --libs pango cairo pangocairo` -o
> cairo-text-on-transparency cairo-text-on-transparency.c
> I'm running cairo 1.10.0, pixman 0.19.7+git20101025.1c23142e and pango
> 1.28.0, albeit all from ubuntu packages.
> I couldn't find any bugs in Bugzilla that seemed relevant - is this
> just a facet of my environment or is there a bug/regression here?
> Thanks in advance,
> Geoff.
> --
> Geoff Youngs

Geoff Youngs
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