[cairo] Polygon clipping problem

cu cairouser at yahoo.com
Sat Feb 14 06:19:07 PST 2009

Thank you for your reply in the bugzilla. I understand the problem now.

I decided to play a bit with cairo code and upped all appropriate sizes
(i.e. 32 bit to 64 bit). This required a lot of busywork in tessellator.
However, as I did it, I realized it won't help (and it did not) unless a
few determinants calculated in tessellator are upped to 128 bit or more.
Since for very wide polygons (with few vertices, like a giant rectangle)
it is likely that two dimensions would be multiplied, we are talking
potentially 10^14 or more.

I am not sure 128 bit calculations are natively supported anywhere, and
in any case this did not seem like a great solution anyway.

So, with that, I have a question:
- It looks like polygons are tessellated fully, not clipped to surface
size, right?
- If I am correct - why? If not - would you point me towards polygon
clipping code?


> It's not expected behaviour. :)  If you could test with the latest 
> stable release cairo 1.8.6 and find it still doesn't work for you, 
> it'd be best to file a bug with specifics and a test case at
> https://bugs.freedesktop.org/
> Cheers,
> Joonas
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> cairo at cairographics.org
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