[metapost] pens and number of points

Peter Rolf indiego at gmx.net
Mon Nov 5 14:36:41 CET 2007

Taco Hoekwater schrieb:
> Peter Rolf wrote:
>> Hi,
>> please excuse my ignorance. Why does MetaPost (1.000) need 18(!) points
>> for drawing a square with a squared pen, while it only needs (the
>> expected) four in case of a circled pen? Is this PS related?
> The suprising thing is that it needs only 4 for the pencircle.
not from my (naive) point of view ;)

> There is special optimization code in metapost because manipulating
> elliptical pens is supported by the PS interpreter itself. That is
> not possible for other types of pens.

> As seen in your second example, it is possible in PS to draw this
> particular case with only 8 points, but that is only true because
> all the pen sides are modulo 90 to the path sides. From a programming
> viewpoint, that is pretty unlikely (and in general, hard to test).
I see that there is no general solution for this problem (pen can be any
closed path). In this special test case using *pencircle* in combination

interim linejoin:= mitered;
interim lincut:= squared;

also results in a nice squared frame with only four points. Suprise again ;)

I have tried some non modulo 90 angles, not equal sized squared pens and
it worked without any problems (this quadrature of a circle [pen] seems
to be supported by PS).
IMO the only point that is speaking for the usage of pensquare is the
possiblity to rotate the pen (untested). If there is more, please let me

> Best wishes,
> Taco
Thanks for the info.

Cheers, Peter

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