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From: jtc@motcad.portal.com (J.T. Conklin)
Newsgroups: comp.lang.postscript
Subject: Stroking thick lines about arcs
Message-ID: <1991Feb20.161757.24206@motcad.portal.com>
Date: 20 Feb 91 16:17:57 GMT
Organization: Computer Signal Corp., San Ramon, California
Lines: 37

I have been observing that stroking an arc with a ``thick'' line results
in some areas of white peeking through the line --- especially about the
outside perimeter --- on two independant PostScript implementation.

From what I understand, the stroke operator follows the path and sets
the pixels within linewith/2 along the perpendicular.  It seems to me
that the interpreters in question do not move along the path in small
enough increments, so some pixels are never considered to be on the 
perpendicular and are not set.

Is this behavior acceptable?  I can't find any documentation on anything
like a stroke step parameter.  Should the step size automagically get
smaller when stroking an arc of sufficient curvature?

I first ran into this problem with the ``GNU T-Shirt Design'', and 
have have created the following test case out of it:

	/inch { 72 mul } def
	/radius 3.5 inch def
	/points 27 def

	4.25 inch 5.5 inch translate
	points 1.5 mul setlinewidth

	newpath
	0 0 radius points 3 div add 0 360 arc
	stroke

	showpage

I would be interested to know if this prints without white specks in the
circle on a real Adobe Interpreter.

	--jtc

-- 
J.T. Conklin    jtc@motcad.portal.com, ...!portal!motcad!jtc