Re: gEDA-dev: teardrops vs polygons

[Peter Clifton <pcjc2-at-NOSPAMcam_dot_ac_dot_uk>]

On Wed, 2008-11-19 at 21:48 -0800, Ben Jackson wrote:
> On Thu, Nov 20, 2008 at 12:39:51AM -0500, DJ Delorie wrote:
> > 
> > I wonder if the polygon clipper is being ignorant of arcs that aren't
> > multiples of 90 degrees?
> 
> That doesn't seem to be the case.  I've run into problems like this before
> when line endpoints overlap.  I've also seen it caused by one straight
> line being made of two segments (normally impossible because the drawing
> code won't create them).  I'm guessing it has to do with all the stacked
> traces.  The fact that it happens there is probably a mathematical
> coincidence that is causing points to align exactly or in just the right
> way.  That's why I suspected (and verified) that a slight change in the
> angle leads to a slight change in the teardrops and avoids the problem.

Any idea why the code breaks for co-incident lines? Unless it is a
fundamental issue, I guess we ought to look for how to fix that, and
then see if it makes this problem go away too.

IIRC, the polygon computation removed degenerate points internally, such
as coincident points or lines, so I'm not sure just how far those lines
will be getting through the computation process.

-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)



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