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From: deadman@garnet.berkeley.edu (Ben Haller)
Newsgroups: comp.lang.postscript
Subject: Re: Setscreen question
Message-ID: <1991Apr17.065854.29763@agate.berkeley.edu>
Date: 17 Apr 91 06:58:54 GMT
References: <91106.223332CXT105@psuvm.psu.edu>
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In article <91106.223332CXT105@psuvm.psu.edu> Christopher Tate
   <CXT105@psuvm.psu.edu> writes:
>Does binding the procedure argument to setscreen have any effect?  I.e. is
>       85 35 {dup mul exch dup mul add 1.0 exch sub} bind setscreen
>equivalent in function to
>       85 35 {dup mul exch dup mul add 1.0 exch sub} setscreen ?
>Does binding the spot function give incorrect results?  If not, it seems
>like binding it should give an appreciable savings in speed, since it's
>called often.  Or, it could be that the setscreen operator binds it itself,
>or some other part of the imaging system does.  In that case, binding it
>would have essentially no effect....

  Well, I don't claim to know very much about this.  But it's my impression
that PostScript takes the setscreen parameters, and immediately converts
that into an internal format that's much faster to use (and may be of a
different frequency, angle, etc, as explained in the book _Real World
PostScript_).  So the spot function would be called perhaps several
hundred times, the results would be tabulated and sorted, resulting in
some internal pattern format for the halftone patterns.
  So my answer is, it shouldn't matter unless you're changing the spot
function often, like within a larger loop.
  To answer the original question, I don't know if it hurts to bind it (I
don't imagine it does, but I have no idea really), and I don't know if
it would speed up that initial tabulation process or not.  Why not try it?

-Ben Haller (deadman@garnet.berkeley.edu)
"Sleeping with your devil mask / Is all I wanna do
 And when I stop, it means I'm through with YOU!  Yeah, yeah you. "
   - Robyn Hitchcock