[comp.sys.sgi] Simulating Transparency using fill patterns on a 4D/25

corkum@csri.toronto.edu (Brent Thomas Corkum) (10/04/90)

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

thant@horus.esd.sgi.com (Thant Tessman) (10/05/90)

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