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2005 Feb 13 16:58

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



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.

> Second of all, what is the significance of the near clipping plane?  So in
> other words, if I hold an apple REALLY REALLY close to my face, if the apple
> isn't past the near clipping plane, I won't see it?  Or does the scene get
> projected onto the near clipping plane (if so, why is it called a "clipping
> plane")?

Yes, if it's outside of the clipping plane, it won't show up.  If
something is too close and obstructs your view of something far away, you
might just want it to disappear.  It's more practical in some situations.

> Also, I'm kind of wondering - if the frustum defines clipping planes, what
> happens if the frustum doesn't coincide with the direction of the camera
> (set by, say, gluLookAt)?   So by default, the camera looks down the
> negative z axis.  Why even bother defining a camera direction if we set a
> viewing volume which, also, seems to define a camera direction?

The frustum, as I recall (don't quote me on it), is relative to the
direction of the camera, so it'll always coincide in the direction of the
camera, unless you define the frustum backwards or something funky like
that.

-Mark


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