[metapost] Filling complex paths

[Tobias Columbus]

On Fri, Oct 17, 2014 at 09:46:34AM +0200, Hans Hagen wrote:
> On 10/17/2014 9:38 AM, Hans Hagen wrote:
> >On 10/16/2014 11:44 PM, Tobias Columbus wrote:
> >>Hi all,
> >>
> >>I am currently writing a piece of software that should spit out some
> >>MetaPost
> >>code. My input are the closed curves of a glyph and I want to produce
> >>MetaPost
> >>code that fills them according to Postscript rules. However, as
> >>MetaPost cannot
> >>handle non-contiguous closed paths, this task seems difficult at least.
> >>
> >>Note that the glyphs come from non-Postscript fonts, so that the MetaPost
> >>"glyph" primitive does not work for me. I also tried "graphictext" as
> >>described
> >>in the Metafun manual but that turned out to be too inaccurate. I
> >>traced the
> >>inaccuracy back to "pstoedit", which is called for "graphictext".
> >>
> >>My attempt was to fiddle around with specials and
> >>withprescript/withpostscript.  This attempt turned out to be nonsense as
> >>addto always writes "stroke" or "fill" and my specials were ignored. I
> >>could, of course, write the whole glyph with specials, but I would
> >>prefer a cleaner solution.
> >>
> >>Has anybody some experience with this kind of problem? How difficult
> >>would it be to add filling of non-contiguous paths to MetaPost?
> >
> >some of this unfilling is supported out of the box
> >
> >\startMPpage
> >
> >path p ; p := fullcircle scaled 10cm .. fullcircle scaled 5cm .. cycle ;
> >fill p ; drawarrow p withcolor red ;
> >
> >currentpicture := currentpicture shifted (-11cm,0) ;
> >
> >path p ; p := fullcircle scaled 10cm .. reverse fullcircle scaled 5cm ..
> >cycle ;
> >fill p ; drawarrow p withcolor red ;
> >
> >\stopMPpage
> 
> btw, with -- it's a bit less fun
> 
> \startMPpage
> 
> path p ; p := fullcircle scaled 10cm -- fullcircle scaled 5cm -- cycle ;
> fill p ; drawarrow p withcolor red ;
> 
> currentpicture := currentpicture shifted (-11cm,0) ;
> 
> path p ; p := fullcircle scaled 10cm -- reverse fullcircle scaled 5cm --
> cycle ;
> fill p ; drawarrow p withcolor red ;
> 
> \stopMPpage
> 

Hi Hans,

Thanks for your answer. I already tried something along the lines you suggest.
However, the result contained lines intersecting the regions of the glyph that
were supposed to be transparent. I thought about writing an algorithm that
constructs a path to the "reverse inner shapes" that does not intersect the
transparent regions. However, that seemed to be daunting and (perhaps) not worth
the hassle. It may also be rather easy to construct such paths with Metapost,
but I am rather new to Metapost...

Tobias

P.S.
Sorry for being too dumb to reply to the mailing list!

> -----------------------------------------------------------------
>                                           Hans Hagen | PRAGMA ADE
>               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>     tel: 038 477 53 69 | voip: 087 875 68 74 | www.pragma-ade.com
>                                              | www.pragma-pod.nl
> -----------------------------------------------------------------
> --
> http://tug.org/metapost/

--