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From: larry@csccat.UUCP (Larry Spence)
Newsgroups: comp.lang.postscript
Subject: Re: Alligning to the device grid
Message-ID: <3540@csccat.UUCP>
Date: 9 Feb 90 20:55:03 GMT
References: <10511@microsoft.UUCP>
Reply-To: larry@csccat.UUCP (Larry Spence)
Organization: Computer Support Corporation. Dallas,Texas
Lines: 28

In article <10511@microsoft.UUCP> chrisg@microsoft.UUCP (Chris GUZAK) writes:
>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)?
> ... other off-by-one inclusive/exclusive questions ...

I would recommend taking a look at the Display PostScript documentation.
The things you're asking about were not really defined well in "printer"
PS, but the DPS documentation takes pains to explicitly define the pixels
that are set when you do a stroke, etc.  The question then becomes, how
much of this applies to current and older implementations?  Well, the
DPS manuals say something to the effect of "this is the latest technology,
all products based on this technology from here on out will behave as we
have described."  Best bet is to look at the DPS docs, then write test
programs to see what actually happens on, say, a LaserWriter.  I think 
that the idea with printer PS was that it's implementation-dependent as
to which pixels get set when things are rasterized, as long as it's all
consistent.  With the introduction of DPS, they decided they really did
need to be explicit about what happens at the device level.

These are my opinions, based on scrutiny of the various PS docs.  Maybe
someone from Adobe can offer a more definitive answer.

-- 
Larry Spence
larry@csccat
...{texbell,texsun,attctc}!csccat!larry