Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!decwrl!sgi!shinobu!odin!cashew.asd.sgi.com!kurt
From: kurt@cashew.asd.sgi.com (Kurt Akeley)
Newsgroups: comp.sys.sgi
Subject: Re: Opaque patterns
Keywords: pattern, GL
Message-ID: <1991May9.153326.17235@odin.corp.sgi.com>
Date: 9 May 91 15:33:26 GMT
References: <1991May8.202442.21658@murdoch.acc.Virginia.EDU>
Sender: news@odin.corp.sgi.com (Net News)
Reply-To: kurt@cashew.asd.sgi.com (Kurt Akeley)
Organization: sgi
Lines: 18

In article <1991May8.202442.21658@murdoch.acc.Virginia.EDU>, acl3k@topaz.cs.Virginia.EDU (Allan Christian Long) writes:
|> Could someone please tell me how to do opaque patterns?

stuff deleted

|> 	I guess I could invert the pattern myself and use two
|> different patterns to get what I want, but I was hoping there
|> would be an easier way.

You're right, the only general technique for implementing opaque
stipple using the Iris GL is to draw twice, once with the pattern
using the foreground color, and again with the inverse of the
pattern, using the background color.  In many cases, however,
it is easier and faster to first clear an entire region to the
background color using no pattern, then draw patterned objects
(such as text) using the foreground color.

-- Kurt