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Subject: Re: [geda-user] FOSDEM
From: Peter Clifton <pcjc2 AT cam DOT ac DOT uk>
To: geda-user AT delorie DOT com
Date: Sun, 08 Feb 2015 16:04:32 +0000
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On Sat, 2015-02-07 at 15:53 -0500, Dave McGuire wrote:
> On 02/07/2015 12:13 PM, Peter Clifton wrote:
> > I'm currently taking time out from the PCB+GL and 3D stuff I want to get
> > merged in order to fix some polygon bugs that are raising their ugly
> > heads. (Long-standing bugs, but perhaps more commonly seen now due to
> > the nm core coordinate switch).
> 
>   ...and thanks for this, by the way!


I'm definitely down the rabbit hole on this one now.

Just to cheer myself up, I read a book chapter yesterday on algorithms
to do boolean operations on 3D BREP solid models. The 3D cases (even for
simple polyhedra, no curves...) makes computing with 2D polygons look so
very simple its almost laughable.

And yet... we hit bugs, because it really isn't that simple.


I think I know the root-cause for the test-case you sent (bad logic in
the contour walk gathering result polygon), and am currently chasing
down the one or two other bugs that its fix exposes. (How to correctly
deal with single vertex touching contours).

The remaining nicety will be fixing the clearance polygon generation to
avoid the rounding errors that created the geometry in my test-cases
that trigger these bugs.

Sometimes I think my efforts here would be better spent writing a solid
test-suite for the polygon algebra, rather than playing whack-a-mole
with these bugs on a case-by-case basis.


Peter

-- 
Peter Clifton <peter DOT clifton AT clifton-electronics DOT co DOT uk>

Clifton Electronics