fgluPerspective(3G)

NAME
     fgluPerspective - set up a perspective projection matrix


FORTRAN SPECIFICATION
     SUBROUTINE fgluPerspective( REAL*4 fovy,
                                 REAL*4 aspect,
                                 REAL*4 zNear,
                                 REAL*4 zFar )


PARAMETERS
     fovy    Specifies the field of view angle, in degrees, in the y
             direction.

     aspect  Specifies the aspect ratio that determines the field of view in
             the x direction.  The aspect ratio is the ratio of x (width) to y
             (height).

     zNear   Specifies the distance from the viewer to the near clipping plane
             (always positive).

     zFar    Specifies the distance from the viewer to the far clipping plane
             (always positive).

DESCRIPTION
     fgluPerspective specifies a viewing frustum into the world coordinate
     system.  In general, the aspect ratio in fgluPerspective should match the
     aspect ratio of the associated viewport. For example, aspect = 2.0 means
     the viewer's angle of view is twice as wide in x as it is in y.  If the
     viewport is twice as wide as it is tall, it displays the image without
     distortion.

     The matrix generated by fgluPerspective is multipled by the current
     matrix, just as if glMultMatrix were called with the generated matrix.
     To load the perspective matrix onto the current matrix stack instead,
     precede the call to fgluPerspective with a call to glLoadIdentity.

     Given f defined as follows:

                                f = cotangent(____)
     The generated matrix is




                    (  ______  0  ____0_____  _____0______   )

NOTES
     Depth buffer precision is affected by the values specified for zNear and
     zFar.  The greater the ratio of zFar to zNear is, the less effective the
     depth buffer will be at distinguishing between surfaces that are near
     each other.  If

                                     r = _____


     roughly log2r bits of depth buffer precision are lost.  Because r
     approaches infinity as zNear approaches 0, zNear must never be set to 0.

SEE ALSO
     glFrustum, glLoadIdentity, glMultMatrix, fgluOrtho2D