MetaFun - Pragma ADE

p := fullcircle scaled (2*length(loc-ori)) shifted ori ;
q := freesquare xyscaled (urcorner s - llcorner s) ;
l := point (xpart (p intersectiontimes (ori--loc))) of q ;
setbounds s to boundingbox s enlarged -freelabeloffset ;
(s shifted -l)
enddef ;
Watch how we temporarily enlarge the bounding box of the typeset label text. We will now test
this macro on a slightly rotated circle, using labels typeset by TEX. The reverse is there purely for
cosmetic reasons, to suit the label texts.
defining
in
funny macros.
and on
go on
Can't we?
We can
pickup pencircle scaled 1mm ;
path p ; p := reverse fullcircle rotated -25 scaled 3cm ;
draw p withcolor .625yellow ; pair cp ; cp := center p ;
freedotlabel (btex \strut We can etex, point 0 of p, cp) ;
freedotlabel (btex \strut go on etex, point 1 of p, cp) ;
freedotlabel (btex \strut and on etex, point 2 of p, cp) ;
freedotlabel (btex \strut in etex, point 3 of p, cp) ;
freedotlabel (btex \strut defining etex, point 4 of p, cp) ;
freedotlabel (btex \strut funny etex, point 5 of p, cp) ;
freedotlabel (btex \strut macros. etex, point 6 of p, cp) ;
freedotlabel (btex \strut Can't we? etex, point 7 of p, cp) ;
Unfortunately we can run into problems due to rounding errors. Therefore we use a less readable
but more safe expression for calculating the intersection points. Instead of using point loc as
endpoint we use loc shifted over a very small distance into the direction loc from ori. In the
assignment to l we replace loc by:
( (1+eps) * arclength(ori--loc) * unitvector(loc-ori) )
13.3 Marking angles
A convenient METAPOST macro is unitvector. When we draw a line segment from the origin to
the point returned by this macro, the segment has a length of 1 base point. This macro has a wide
range of applications, but some basic knowlegde of vector algebra is handy. The following lines
of METAPOST code demonstrate the basics behind unitvectors.
Marking angles A few applications
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