Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!microsoft!chrisg
From: chrisg@microsoft.UUCP (Chris GUZAK)
Newsgroups: comp.lang.postscript
Subject: Alligning to the device grid
Message-ID: <10511@microsoft.UUCP>
Date: 8 Feb 90 18:41:17 GMT
Reply-To: chrisg@microsoft.UUCP (Chris GUZAK)
Organization: Microsoft Corp., Redmond WA
Lines: 25

How is the postscript device space pixel grid defined.  If you
are at device coordinate 0,0 are on at the center point of a
pixel or on the upper left corner (on the box that bounds the
pixel)?

Also, how does clipping work in device space?  When you trace
a path over some device coordinates (given the answer to
the above question) when do pixels get set or not (is the
clipping inclusive of the path or exclusive)?

The specific example that I am curious about is for the case
of a rect, 1 pixel in height. 

0 0 moveto
10 0 rlineto
0 1 rlineto
-10 0 rlineto
closepath
clip

Assumiming you are have set up CTM so that device coordinates
map to user coordinates (and the reverse) what is the result when
you draw over the above clipping path?

Chris Guzak