Re: [artworks] A funny point in intersections

  • From: Tim Powys-Lybbe <tim@xxxxxxxxx>
  • To: artworks@xxxxxxxxxxxxx
  • Date: Tue, 22 Feb 2011 21:02:08 +0000

On 22 Feb at 20:19, Martin Wuerthner <lists@xxxxxxxxxxxxxxx> wrote:

> In message <mpro.lh0q170001fc40p8e.tim@xxxxxxxxx>
>           Tim Powys-Lybbe <tim@xxxxxxxxx> wrote:
> 
> > Time for something on ArtWorks.
> 
> > I think I have at least got the hang of intersections and am
> > delighted with this facility for making it easy to do complicated
> > drawings.
> 
> > However there is an odd extra point that keeps on creeping in.
> 
> > [...]
> 
> > The odd thing is the additional point of the Intersection on its
> > curved section.  There is no such point on the curvature of the
> > original shield.  The two curved parts of the shield are simple
> > beziers.  This additional point can be a slight nuisance when trying
> > to make minor subsequent alterations to the intersected object.  But
> > if the point is deleted that segment reverts to a straight line.
> 
> > Does this additional point have to be there?
> 
> It does not have to be there but this is how the intersection
> algorithm in ArtWorks works. Curves that are not cut through by the
> clipping path remain untouched, only intersected curves are modified
> to end in the intersection point, but in addition to that they usually
> get another anchor point near the intersection. There is no easy way
> to prevent this from happening.
> 
> Xara Xtreme did exactly the same for a long time. Version 3.2 still
> behaved as ArtWorks and added these extra points (not surprising since
> the intersection routines were written by Gavin who also wrote those
> used in ArtWorks). Xtreme 4.0 was the first version that used an
> improved intersection algorithm producing the optimal result without
> any extra points.

Many thannks for that answer.  I shall rabbit no more!

-- 
Tim Powys-Lybbe                                           tim@xxxxxxxxx
             for a miscellany of bygones: http://powys.org/
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