C SPECIFICATION

       void gluLookAt( GLdouble eyeX,
                       GLdouble eyeY,
                       GLdouble eyeZ,
                       GLdouble centerX,
                       GLdouble centerY,
                       GLdouble centerZ,
                       GLdouble upX,
                       GLdouble upY,
                       GLdouble upZ )

PARAMETERS

       eyeX, eyeY, eyeZ
                       Specifies the position of the eye point.

       centerX, centerY, centerZ
                       Specifies the position of the reference point.

       upX, upY, upZ   Specifies the direction of the up vector.

DESCRIPTION

       gluLookAt  creates a viewing matrix derived from an eye point, a refer-
       ence point indicating the center of the scene, and an UP vector.

       The matrix maps the reference point to the negative z axis and the  eye
       point  to  the  origin.   When a typical projection matrix is used, the
       center of the scene therefore maps to the center of the viewport.  Sim-
       ilarly,  the  direction  described  by the UP vector projected onto the
       viewing plane is mapped to the positive y axis so that it points upward
       in  the  viewport.   The  UP vector must not be parallel to the line of
       sight from the eye point to the reference point.

       Let

            centerX - eyeX
        F = centerY - eyeY
            centerZ - eyeZ

       Let UP be the vector (upX, upY, upZ).

       Then normalize as follows: f = F/ || F ||

       UP' = UP/|| UP ||

       Finally, let s = f X UP', and u = s X f.

       M is then constructed as follows:

             s[0]    s[1]    s[2]    0
             u[0]    u[1]    u[2]   0
                                                                 GLULOOKAT(3G)