[cairo] Avoiding seams (again)

Carl Worth cworth at cworth.org
Wed Mar 22 14:25:18 PST 2006

On Wed, 22 Mar 2006 22:13:56 +0100 (CET), Timothée Lecomte wrote:
> Do you remember the thread about avoiding seams between paths a months ago ?

I do. I think it's an interesting class of problem.

> - stroke each path
>  Good : gives expected result

I'd like to disagree on that point. Stroking each shape will still
introduce seams if there is transparency involved. And even with
entirely opaque objects can result in "lumpiness" (that is,
poor-quality antialiasing), on the border of the composite object,
where multiple primitives meet.

>  Good : no seam, reasonably fast

Those are looking like some good characteristics to work from as a
starting point.

>  Problem : have to draw front-to-back to a separate context whereas
> gnuplot gives me the instructions back-to-front, so it adds some overhead.
> But  I also get white lines artifacts.
> See : http://tipote.free.fr/wxt-saturate2.png
> Do you have other ideas, or a solution to the artefacts problem with

It could be just a bug that we hadn't noticed before. I'm not sure
that the SATURATE stuff has seen a lot of correctness testing yet.

If you could replicate this behavior in as minimal a test case as
possible, that would be very helpful.

> Thank you very much for your help, and thank you for the great library
> that Cairo is.

Thanks for your report. And I'm quite glad that you are having fun
with cairo.

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