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From: thant@horus.esd.sgi.com (Thant Tessman)
Newsgroups: comp.sys.sgi
Subject: Re: Simulating Transparency using fill patterns on a 4D/25
Message-ID: <1990Oct4.181329.10277@odin.corp.sgi.com>
Date: 4 Oct 90 18:13:29 GMT
References: <1990Oct3.144925.12691@jarvis.csri.toronto.edu>
Sender: news@odin.corp.sgi.com (Net News)
Reply-To: thant@horus.esd.sgi.com (Thant Tessman)
Organization: Silicon Graphics Inc.
Lines: 53

In article <1990Oct3.144925.12691@jarvis.csri.toronto.edu>,
corkum@csri.toronto.edu (Brent Thomas Corkum) writes:
> 
> A while back someone told me that you could simulate transparency on 
> a 4D/25 by using fill patterns on polygons, and making the 
> background transparent. What I want to know is has anyone done
> this and what parameters to what gl routines do I need to use.
> 
> Brent Corkum
> corkum@csri.toronto.edu


See 'defpattern' and 'setpattern.'


#define HALFTONE 1
#define QUARTERTONE 2

short halftone[] = {

	0x5555, 0xaaaa, 0x5555, 0xaaaa,
	0x5555, 0xaaaa, 0x5555, 0xaaaa,
	0x5555, 0xaaaa, 0x5555, 0xaaaa,
	0x5555, 0xaaaa, 0x5555, 0xaaaa,
};


short quartertone[] = {

	0x1111, 0x0000, 0x4444, 0x0000,
	0x1111, 0x0000, 0x4444, 0x0000,
	0x1111, 0x0000, 0x4444, 0x0000,
	0x1111, 0x0000, 0x4444, 0x0000,
};


main() {

	/*...*/
	defpattern(HALFTONE, 16, halftone);
	defpattern(QUAETERTONE, 16, quartertone);

	/*...*/
	setpattern(HALFTONE);
	draw_half_transparent_thing();

	/* etc */
}


Good luck,

thant