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From: Steve Baker <sbaker@link.com>
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To: Multiple recipients of list OPENGL-GAMEDEV-L <OPENGL-GAMEDEV-L@fatcity.com>
Subject: Re: How To Q: Off-screen object culling.
Date: Mon, 20 Apr 1998 07:50:34 -0800
On Sat, 18 Apr 1998, Jason Maskell wrote:
> This is probably an FAQ, but I'm to the point now where I need to be
> able to tell when one of my objects is offscreen and not even send it
> down the pipe. This would be pretty simple if I was using glFrustum,
> but I'm not at the moment. I could switch, but I haven't quite got my
> head around how to get the same results as I get using glPerspective..
> If someone can point me to some code that does some simple pre-culling,
> I would be most grateful.. >
Well, if you can do it with glFrustum then you can do it with
gluPerspective. Note that gluPerspective simply calls glFrustum.
It's like this:
void APIENTRY gluPerspective( GLdouble fovy, GLdouble aspect,
GLdouble zNear, GLdouble zFar )
{
GLdouble xmin, xmax, ymin, ymax;
ymax = zNear * tan( fovy * M_PI / 360.0 );
ymin = -ymax;
xmin = ymin * aspect;
xmax = ymax * aspect;
glFrustum( xmin, xmax, ymin, ymax, zNear, zFar );
}
[This is actually the source code for gluPerspective from the Mesa
library - but since it only involves regular OpenGL API, it should
work on any OpenGL implementation]
> BTW, I've bought the red book finally...
Always a good move. I have yet to hear anyone who regretted it.
Steve Baker (817)619-8776 (Vox/Vox-Mail)
Raytheon Systems Inc. (817)619-4028 (Fax)
Work: SBaker@link.com http://www.hti.com
Home: SJBaker1@airmail.net http://web2.airmail.net/sjbaker1
--
Author: Steve Baker
INET: sbaker@link.com
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