[vox-tech] OpenGL: Frustums

[Peter Jay Salzman]

On Sun 13 Feb 05,  4:58 PM, Mark K. Kim <lugod at cbreak.org> said:
> On Sun, 13 Feb 2005, Mark K. Kim wrote:
> 
> > On Sun, 13 Feb 2005, Peter Jay Salzman wrote:
> > [snip]
> > > First of all, why "-near" and not "near"?  That's such a strange definition
> > > I can't help but feel it's a typo.
> >
> > Not sure.  My v1.2 redbook says the same thing.
> 
> Oh, I think I figured out why it's -near.  I think it's because the Z axis
> comes out of your screen, so the direction you're looking at is in the -Z
> axis direction.  "near" is in the direction you're looking at, therefore
> the plane you're defining is -near relative to the axis.
> 
> -Mark

I don't think I buy that.  It's true that the default viewing matrix is at
the origin looking down the -z axis, but that's just one special case.  I
can't believe that the designers would implement a fundamental definition
based on a default viewing angle?   So if the camera turns around and faces
the positive z axis...

Most of the time in a 3D world, you first draw the scene, then you position
and point the camera.  So most of the time the camera really isn't going to
be at the origin anyhow.  (I think.)
 
Wierd...

Pete

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