GLdouble aspect,
                                       GLdouble zNear,
                                       GLdouble zFar )

PARAMETERS
       fovy    Specifies  the  field of view angle, in degrees, in the y direc‐
               tion.

       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
       gluPerspective specifies a viewing frustum  into  the  world  coordinate
       system.  In general, the aspect ratio in gluPerspective 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 gluPerspective is multipled by the current ma‐
       trix, just as if glMultMatrix were called with the generated matrix.  To
       load  the perspective matrix onto the current matrix stack instead, pre‐
       cede the call to gluPerspective with a call to glLoadIdentity.

       Given f defined as follows:

                                  f=cotangent(____)
       The generated matrix is

                         ⎝______ 0      0           0      ⎠
                             0   f      0           0
                             0   0 __________ _____________
                             0   0    −1            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 ap‐
       proaches infinity as zNear approaches 0, zNear must never be set to 0.