C SPECIFICATION

       void GLAPIENTRY glOrtho( GLdouble left,
                                GLdouble righ )

PARAMETERS

       left, righ Specify  the  coordinates  for  the  left and right vertical
                  clipping planes.

       _param3, _param4
                  Specify the coordinates for the bottom  and  top  horizontal
                  clipping planes.

       _param5, _param6
                  Specify  the distances to the nearer and farther depth clip-
                  ping planes.  These values are negative if the plane  is  to
                  be behind the viewer.

DESCRIPTION

       glOrtho describes a transformation that produces a parallel projection.
       The current matrix (see glMatrixMode) is multiplied by this matrix  and
       the  result replaces the current matrix, as if glMultMatrix were called
       with the following matrix as its argument:

              r_i_g_h__l_e_f_t_           0                     0           tx



















                 0      _e_q_n_p_a_r_a_m____e_q_n_p_a_r_a_m__           0           ty

























                 0               0                     0            1

       where
                                    tx=-r<I>r_i<I>i_g<I>g_h<I>h__l<I>l_e<I>e_f<I>f_t<I>t_

                              ty=-_e<I>e_q<I>q_n<I>n_p<I>p_a<I>a_r<I>r_a<I>a_m<I>m____e<I>e_q<I>q_n<I>n_p<I>p_a<I>a_r<I>r_a<I>a_m<I>m__

                              tz=-_e<I>e_q<I>q_n<I>n_p<I>p_a<I>a_r<I>r_a<I>a_m<I>m____e<I>e_q<I>q_n<I>n_p<I>p_a<I>a_r<I>r_a<I>a_m<I>m__

and  (righ,  _param4,  -_param5) specify the points on the near clipping plane
that are mapped to the lower left and  upper  right  corners  of  the  window,
respectively,  assuming that the eye is located at (0, 0, 0).  -_param6 speci-
fies the location of the far clipping plane.  Both _param5 and _param6 can  be
either positive or negative.

       GL_INVALID_OPERATION is generated if glOrtho is  executed  between  the
       execution of glBegin and the corresponding execution of glEnd.

       glGet with argument GL_MATRIX_MODE
       glGet with argument GL_COLOR_MATRIX
       glGet with argument GL_MODELVIEW_MATRIX
       glGet with argument GL_PROJECTION_MATRIX
       glGet with argument GL_TEXTURE_MATRIX

       glFrustum, glMatrixMode, glMultMatrix, glPushMatrix, glViewport