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From: Jens-Uwe Morawski <morawski@gmx.net>
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Subject: MetaFun refill/do_repath bug
Date: Mon, 16 Sep 2002 17:31:30 +0200
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Ahoi Hans,

i wrote an article for the magazine of the german TUG that explains
some advanced features of MetaPost. Esp. it explains the
within,pathpart,penpart... stuff. In the article i give an example
that refills all filled elements of a picture with a new color.

The article is not yet published, but one who has proof-read the
article told me that an equal macro is provided by MetaFun. A little
bit surprised, since i thought that i know most of the MetaFun
features, i've tried the "refill" macro and was surprised again, since
it does not work correctly (IMO). The problem is that the macro
"do_repath" does not handle clipped and bounded graphic elements
correctly.

Your macro ignores totally that clipped and bounded elements
contain again some more graphic elements, i.e. lines, filled
paths etc. Therefore the macro has to be applied recursively to
these elements too. Furthermore the pathpart of a clipped
or bounded object has to be applied only to the elements in
that object and not to the whole picture.

Please find below a MP-file that illustrates what i mean.
It compares the macro "uniformfilled" from my article with
your "refill".

Best,
  Jens

%%% ---snip--- 

input metafun ;

primarydef p uniformfilled c =
	begingroup
	save t, f, s ;
	picture t, s ;
	t := nullpicture ; color f ;

	for i within p :
		f := (redpart i, greenpart i, bluepart i) ;
		if bounded i :
			s := i uniformfilled c ;
			setbounds s to pathpart i ;
			addto t also s ;
		elseif clipped i :
			s := i uniformfilled c ;
			clip s to pathpart i ;
			addto t also s ;
		elseif stroked i : 
			addto t doublepath pathpart i 
			  dashed dashpart i withpen penpart i 
			  withcolor f ;
		elseif filled i : 
			addto t contour pathpart i 
			  withcolor c ;
		else:
			addto t also i ;
	     fi ;
	endfor; t endgroup
enddef;

picture pic[] ;

%-- a clipped picture
pic[0] := nullpicture ;
addto pic[0] contour ( unitsquare scaled 2cm )
	withcolor green ;
addto pic[0] contour ( unitsquare scaled 2cm shifted (-2cm,-2cm) )
	withcolor green ;
addto pic[0] contour ( unitsquare scaled 2cm shifted (0,-2cm) )
	withcolor red ;
addto pic[0] contour ( unitsquare scaled 2cm shifted (-2cm,0) )
	withcolor red ;

clip pic[0] to fullcircle scaled 4cm ;

%-- the base picture
pic[1] := nullpicture ;
addto pic[1] contour
	( unitsquare xscaled 5cm yscaled 1cm shifted (-2.5cm,1cm) )
	withcolor blue ;
addto pic[1] contour
	( unitsquare xscaled 5cm yscaled 1cm shifted (-2.5cm,-2cm) )
	withcolor blue ;
addto pic[1] also pic[0] ;
addto pic[1] doublepath fullcircle scaled 4cm
	withpen pencircle scaled 3pt;

%-- "uniformfilled" applied to the base picture
pic[2] := pic[1] uniformfilled .6white ;

%-- "refill" applied to the base picture
pic[3] := pic[1] ;
refill pic[3] withcolor .6white ;

beginfig(1);

label.top(pic[1],origin) ;
label.bot("original",origin) ;

label.top(pic[2],(5.3cm,0)) ;
label.bot("uniformfilled",(5.3cm,0)) ;

label.top(pic[3],(10.6cm,0)) ;
label.bot("MetaFun/refill",(10.6cm,0)) ;

endfig;
end