On Tue, Sep 10, 2019 at 03:23:43PM +0200, Jens Axel Søgaard wrote:
> Den tir. 10. sep. 2019 kl. 14.54 skrev George Neuner <gneun...@comcast.net>:
> >
> > Or create a region with a hole through it and use it to clip the drawing.
> >
> Great suggestion. That's much better than using pict->bitmap.
> I have extended "clipped" to handle regions defined by more than one path.
> Now (clipped c ... p) will make a region from the curves c ... and use
> the region to clip the pict p. Most common uses:
>    (clipped c p)          the part of p inside c
>    (clipped c1 c2 p)   the part of p between c1 and c2 (if c2 is inside c1)

Does that mean the part of p that is inside c1 and outside c2? (which 
would be meaningful even if c1 and c2 intersect?  That might happen 
because of numerical instability.)

> The example now becomes:
> #lang racket
> (require metapict metapict/polygons)
> (define (cutout p x y r)
>   (defv (w h) (pict-size p))
>   (with-window (window 0 w 0 h)
>     (clipped (rectangle (pt 0 0) (pt w h))
>              (circle (pt x y) r)
>              p)))
> (set-curve-pict-size 400 400)
> (def p (brushcolor "red" (fill (regular-polygon 5))))
> (cutout p 200 200 50)
> Before only one curve was supported and the result of clipped was the
> interior,
> so the old clipped couldn't cut holes.
> /Jens Axel

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