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(Typically) Projection Transformations:
One of the following is typically applied in projection mode.
This sets the manner in which projection (either perspective or
parallel) is performed. In all cases the arguments are of type
GLdouble.
 glOrtho(left, right, bottom, top, near, far):

Generate an orthogonal projection transformation (projecting
along the z axis) where the clipping region consists of points
satisfying left <= x <= right,
bottom <= y <= top and
near <= z <= far. All other points
are clipped away.
 gluOrtho2D(left, right, bottom, top):

A two dimensional version of glOrtho(), when the
zcoordinates are irrelevant. (It sets near = 1 and
far = +1.)
 glFrustum(left, right, bottom, top, near, far):

Generate a perspective projection transformation and compose it
with the current transformation. The parameters specify the
bounds of the viewing frustum. The arguments near and
far are the distances to the near and far clipping planes
along the zaxis. The other arguments specify the bounds of
the viewing rectangle on the near clipping plane.
 gluPerspective(fovy, aspect, zNear, zFar):

A more restrictive, but more natural version of
glFrustum(). It generates a perspective projection
transformation for the given updown field of view (in degrees),
for a window with the given aspect ratio (width/height) and the
given near and far clipping planes. It composes this with the
current transformation.
Please report any errors or send comments to
Dave Mount
Last updated: Sat, Feb 8, 2003.