[cairo] Incorrect rendering of the edges of overlapping polygons

David Benbennick dbenbenn at gmail.com
Sun Dec 4 17:36:30 PST 2005

On 12/4/05, mental at rydia.net <mental at rydia.net> wrote:
> Quoting David Benbennick <dbenbenn at gmail.com>:
> > Is this a known bug? Is there interest in fixing it?
> It's a limitation of the algorithms which are available to us.

For what it's worth, it appears that Postscript renderers don't suffer
from this problem.  At least, Metapost, which produces Postscript
output, doesn't have this problem.

> The simplest approach is to simply render the entire scene at a higher
> resolution without edge antialiasing and then filter the resulting
> image down to the target resolution.

That isn't much of a solution, since it makes sharp edges fuzzy,
discarding the big benefit of vector graphics.

> Unlike the alpha-coverage-approximation approach Cairo uses by
> default (which introduces these seams), no FSAA approach can be
> used incrementally.

What does that mean?  If necessary, Cairo can certainly render the
first n% of the commands it receives, regardless of what rendering
algorithm it uses.  Is incremental rendering something that users are
actually aware of?

Also, you write "by default".  Is there any non-default method available?

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