Darren New <dne### [at] sanrrcom> wrote:
> As far as I can figure, there's no way to represent near and far clipping 
> planes in a transformation matrix, right? The camera itself (in some sense) 
> has to carry them along separately?  I.e., the near and far clipping planes 
> don't get represented anywhere in a normal 4x4 transformation matrix?

  If you think about it, how could it ever work?

  The idea of a transformation matrix is that it can be used to transform
a point from one coordinate system to another via a simple matrix
multiplication (where the point is represented by a 1xn matrix and the
transformation matrix is an nxn one). When we are talking about 3D points,
a 3x3 transformation matrix can be used to perform any affine transformations,
while a 4x4 one can additionally be used for things like translations and
perspective projection.

  The point is that a *point* is transformed from one coordinate system to
another.

  Now, how would you apply a "clipping plane" to a point? Literally
speaking a clipping plane would make a point disappear if the point is
on the wrong side of the plane. How do you make a point disappear via
a matrix multiplication? Multiplying a point by a matrix always results
in another point. Multiplication doesn't make a point disappear. (It
doesn't even make much sense in that context.)

  (Of course in practice you seldom clip individual points. In practice
what get clipped are lines and polygons, which is a whole different
issue which can certainly not be solved via a single matrix multiplication.)

  If what you are asking is whether a 4x4 matrix could carry clipping
plane coorinates inside itself without affecting the transformation
otherwise, I'd say that's not possible. I don't think it could carry
that much information.

-- 
                                                          - Warp

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