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From: stew@endor.UUCP
Newsgroups: comp.sys.mac
Subject: Re: Re: Laserwriter, PostScript, and Patterns
Message-ID: <1513@husc6.UUCP>
Date: Fri, 27-Mar-87 23:40:46 EST
Article-I.D.: husc6.1513
Posted: Fri Mar 27 23:40:46 1987
Date-Received: Sun, 29-Mar-87 18:45:39 EST
References: <2302@cec2.UUCP> <345@gssc.UUCP> <465@batcomputer.tn.cornell.edu> <360@gssc.UUCP>
Sender: news@husc6.UUCP
Reply-To: stew@endor.UUCP (Stew Rubenstein)
Organization: Aiken Computation Lab Harvard, Cambridge, MA
Lines: 39


Obviously, it's possible to fill an area with a pattern;  the Macintosh
Laser Prep does it.  Look at that for an example.  Basically, you
use the setscreen operator to define a halftone screen with a procedure
that orders the pixels in the halftone screen cell so that the pixels
you want white in your pattern are the ones that the fill operator
whitens to form the halftone screen.

Normally, the standard spot function is used which is optimized for the
device.  You can get "line screen" or "dot screen" effects fairly easily
by redefining the spot function.  Try:

	/shape{newpath
		0 0 moveto 20 100 lineto 80 100 lineto 100 0 lineto
		closepath fill
	}def
	gsave
	50 50 translate
	/dotFreq 10.0 def
	dotFreq 0 {dup mul exch dup mul add 1 exch sub} setscreen
	0.05 0.05 0.99 {setgray shape 72 dotFreq div dup 3 mul translate}for
	grestore

If you just want to get patterns with 72 dpi resolution like you get
from quickdraw, use the routines defined in the Laser Prep: try
something like

	md begin
	gsave
	50 300 translate
	48<C06030180C060381>pat  % a simple striped pattern
	shape
	grestore
	showpage

where 48 is the number of zero bits in the 8-byte pattern.

Obtaining patterns finer-grained than that by modifying the Laser Prep
definitions for pat is left as an exercise for the reader.