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2005 Feb 13 20:52

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Re: [vox-tech] OpenGL: Frustums
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Re: [vox-tech] OpenGL: Frustums

On Sun 13 Feb 05,  4:58 PM, Mark K. Kim <lugod@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.)


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