[metapost] glyph operator and contours order

[Laurent Méhats]

Hello,

The MetaPost manual explains that the glyph operator works in such a way
that "all black contours are drawn before white contours". This is
problematic in the case of glyphs in which a black contour lies inside a
white contour, for the inside black contour gets "erased" by the white
one. However, since the contours are accessible, it is possible to fill
them manually in a convenient order.

I believe that glyph contours don't intersect each-other, nor
self-intersect (is that always true ?), so my question would be: given two
non intersecting nor self-intersecting cycles, is there a proper way to
decide whether one lies inside the other ?

Regards,
Laurent Méhats


Here is an example of a problematic glyph.

--%<-- test.mp
verbatimtex%&latex
\documentclass[12pt]{article}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\begin{document}
etex;

beginfig(0)
% 'etex .. btex' Theta
  picture pct;
  pct:=btex\Huge$\Theta$etex;
% glyph operator Theta
  picture glp;
  glp:=nullpicture;
  for tkn within pct:
    addto glp also glyph ASCII textpart tkn of fontpart tkn
      scaled (fontsize fontpart tkn/1000)
      xscaled xxpart tkn
      yscaled yypart tkn;
  endfor
% contours
  numeric num;
  path ctr[];
  num:=0;
  for tkn within glp:
    ctr[num]:=pathpart tkn;
    num:=num+1;
  endfor
% hand-filled contours
  picture hnd;
  hnd:=nullpicture;
  addto hnd contour ctr[1];
  addto hnd contour ctr[2] withcolor background;
  addto hnd contour ctr[0];
% comparisons
  draw pct;
  draw glp shifted lrcorner pct;
  draw hnd shifted (2*lrcorner pct);
endfig;

end
--%<-- test.mp