MetaFun - Pragma ADE

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Often I make such helpers in the process of writing larger drawing systems. Take crossed:
path p ; p := origin crossed 1cm ;
drawpath p ; drawpoints p ;
p := (origin crossed fullcircle scaled 2cm crossed .5cm) shifted (3cm,0) ;
drawpath p ; drawpoints p ;
These examples demonstrate that a path is made up out of points (something that you probably
already knew by now). The METAPOST operator of can be used to ‘access' a certain point at a curve.
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path p ; p := fullsquare xyscaled (3cm,2cm) randomized .5cm ;
drawpath p ; drawpoints p ; drawpointlabels p ;
draw point 2.25 of p withpen pencircle scaled 5mm withcolor .625red ;
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To this we add two more operators: on and along. With on you get the point at the supplied
distance from point 0; with along you get the point at the fraction of the length of the path.
path p, q, r ;
p := fullsquare xyscaled (2cm,2cm) randomized .5cm ;
q := p shifted (3cm,0) ; r := q shifted (3cm,0) ;
drawpath p ; drawpoints p ; drawpointlabels p ;
drawpath q ; drawpoints q ; drawpointlabels q ;
drawpath r ; drawpoints r ; drawpointlabels r ;
pickup pencircle scaled 5mm ;
draw point 2.25 of p withcolor .625red ;
draw point 2.50cm on q withcolor .625yellow ;
draw point .45 along r withcolor .625white ;
Beware: the length of a path is the number of points minus one. The shapes below are constructed
from 5 points and a length of 4. If you want the length as dimension, you should use arclength.
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Welcome to MetaPost Some extensions
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We will now play a bit with simple lines. With cutends, you can (indeed) cut off the ends of a
curve. The specification is a dimension.
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