[cairo] Rendering error in cairo-1.5.10 and up
cworth at cworth.org
Thu Apr 24 09:07:05 PDT 2008
On Thu, 24 Apr 2008 16:54:47 +0200, Franz Schmid wrote:
> sorry to bother you with another cairo bug. I discovered that
> in cairo-1.5.10 and up (including 1.6.4) the cairo_set_dash function
> causes rendering errors with dashed closed polygons.
> Please see http://bugs.scribus.net/view.php?id=6971
> for screenshots and comments.
Yikes! That looks like quite a bug.
> The only workaround for that problem is not to close the polygon,
> but that is simply not acceptable.
> The last working version of cairo is 1.5.8
Cairo 1.5.10 did include a stroking optimization:
and also something specific to dashed stroking:
It's not an exactly an easy change to simply revert for testing,
though, since it had several followups to fix some problems in the
All five of those changes made it into 1.5.10. But the fact that 3
followups were necessary does lead me to suspect that this new bug
might be yet another problem exposed by this stroking
optimization. (And, Vlad, if I'm wrong in my guess I apologize in
advance for pointing at your commits!)
Franz, What's really going to help us here if you can provide for us a
sequence of cairo calls to replicate the bug. Perhaps you've got easy
facilities in scribus for dumping out a path? (along with scale and
stroke parameters like line width, join style, etc.)
Otherwise the libcairowrap utility (or maybe it's named cairo-trace
these days) can be helpful by using an LD_PRELOAD to dump cairo calls
while running scribus live. Here's one version of that:
git clone git://annarchy.freedesktop.org/~ickle/cairo-trace
Everyone, is Chris's version here the most up to date thing? We should
put this into /git to make it more clear which version is
official. And we could really use a wiki page on cairographics.org
explaining how to use this.
Thanks for the report, Franz. Sorry about the bug, and I hope we'll be
able to get it fixed quickly.
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