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2005 Feb 14 21:36

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

On Mon, 14 Feb 2005, Peter Jay Salzman wrote:
> You can easily construct a series of matrix operations so that the order of
> operations in the pipeline comes out exactly in the SAME order as you'd
> think.

You're absoluately right from the mathematical point of view.  However,
there are other issues in 3D graphics that restrict certain pipeline
operations from moving before/after another operation.  For example, since
any vertex outside the frustum isn't drawn, it's in the best interest of
the graphics pipeline to calculate the location of the vertex relative to
the frustum as early as possible to determine whether to the vertex can be
dropped out of the pipeline, which can potentially lead to speed
optimization, and which certainly leads to space optimization.

Also, the frustum is supposed to follow around the camera, because it's
supposed to be the area that the camera sees.  The fact that the "far"
argument exists is merely for operation optimization sake (drop anything
from the pipeline that's too far from the camera's view therefore won't be
seen anyway), and I'm not sure why "near" exists but as I guessed earlier
perhaps for convenience in certain effects.

That fact (or my misconception) that the redbook defines "near" as "-near
relative to the original coordinate of the camera" is simply a notational
convention the book uses so I wouldn't think too much about it.  I'd just
try it out and see if that's really the notation the book is using.

> You said the magic words: "try it out".   :)   It's so much easier to be
> spoonfed...    ;-)
> But I'll give it a try (and if you're interested, report back).  I may not
> get to it till Wednesday.

Sounds good.  If I were to try it I probably won't get to it for a few
years, until I have to use it =P

> It's a good thing my
> calculus is so strong...I can walk into the classroom and "wing it" for most
> topics.

I wish my math skills were as strong as yours.  I'm having a dreadful time
in the robotics control course.  Though interesting, we're zipping through
all the math all too fast: Matrices (not so bad), linear algebra (not so
bad), Laplace transforms (grr... ok fine), gradients (aww man), Jacobian
(??!!), INVERSE Jacobian what the heck, and what in the world is a
PSEUDO-inverse Jacobian... -_-'


PS: I special ordered the new LaTeX companion book... yeah, it was long
overdue for a new edition.  It should arrive sometime this week wee~!

Mark K. Kim
AIM: markus kimius
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