C SPECIFICATION

       GLint gluUnProject( GLdouble winX,
                           GLdouble winY,
                           GLdouble winZ,
                           const GLdouble *model,
                           const GLdouble *proj,
                           const GLint *view,
                           GLdouble* objX,
                           GLdouble* objY,
                           GLdouble* objZ )

PARAMETERS

       winX, winY, winZ
                       Specify the window coordinates to be mapped.

       model           Specifies  the modelview matrix (as from a glGetDoublev
                       call).

       proj            Specifies the projection matrix (as from a glGetDoublev
                       call).

       view            Specifies  the viewport (as from a glGetIntegerv call).

       objX, objY, objZ
                       Returns the computed object coordinates.

DESCRIPTION

       gluUnProject maps the specified window coordinates into object  coordi-
       nates using model, proj, and view.  The result is stored in objX, objY,
       and objZ. A return value of GL_TRUE indicates success; a  return  value
       of GL_FALSE indicates failure.

       To  compute the coordinates (objX, objY, and objZ), gluUnProject multi-
       plies the normalized device coordinates by the inverse of model*proj as
       follows:


                                2(winX - view[0])
                                -----------------  - 1
                                     view[2]

           objX                 2(winY - view[1])
           objY   =  INV(PM)    -----------------  - 1
           objZ                      view[3]
            W
                                     2(winZ)       - 1

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