[metapost] Problem with generating EPS from MetaFont source

Boguslaw Jackowski B_Jackowski at GUST.org.pl
Sat Dec 4 15:17:19 CET 2010


DL> Metapost has longstanding bugs in the handling of polygonal pens. It
DL> tries to calculate the path of the outermost corner, which can switch
DL> from one corner to another along a curve. Unfortunately, this is a 
DL> rather unstable mathematical problem and metapost frequently gets it 
DL> wrong. Sometimes an infinitessimal rotation of the pen causes it to 
DL> come out right.

... and vice versa. :)

It's true that the problem of calculating the envelope of the polygonal
pen is mathematically unstable (it is not an exception in the realm of
discrete geometry), but this does not explain the bugs -- the 
representation of the path (pen's envelope) may change unstably but 
not its visual appearance. Or I am mistaken?

Cheers -- Jacko

Ps. Some theoretical details about polygonal ("Metafont-oriented") pens 
can be found in: John D. Hobby, Rasterizing Curves of Constant Width, JACM 
36(2), 1989.

  Bogus\l{}aw Jackowski: B_Jackowski at GUST.ORG.PL
  Hofstadter's Law: It always takes longer than you expect, even
                    when you take into account Hofstadter's Law.

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