GLFRUSTUM(3G) GLFRUSTUM(3G)

NAME
       ggllFFrruussttuumm - multiply the current matrix by a perspective matrix


CC SSPPEECCIIFFIICCAATTIIOONN
       void ggllFFrruussttuumm( GLdouble left,
                       GLdouble right,
                       GLdouble bottom,
                       GLdouble top,
                       GLdouble zNear,
                       GLdouble zFar )


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

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

       zNear, zFar Specify  the  distances  to the near and far depth clipping
                   planes.  Both distances must be positive.

DESCRIPTION
       ggllFFrruussttuumm describes a perspective matrix that  produces  a  perspective
       projection.   The  current  matrix  (see ggllMMaattrriixxMMooddee) is multiplied by
       this  matrix  and  the  result  replaces  the  current  matrix,  as  if
       ggllMMuullttMMaattrriixx were called with the following matrix as its argument:







          2 zNear
        ------       0              A              0
        right - left

                        2 zNear
            0         ------        B              0
                      top - bottom



            0              0              C              D


            0              0              -1             0

                         A = (right + left) / (right - left)

                         B = (top + bottom) / (top - bottom)

                        C = - (zFar + zNear) / (zFar - zNear)

                        D = - (2 zFar zNear) / (zFar - zNear)

       Typically, the matrix mode is GGLLPPRROOJJEECCTTIIOONN, and (left, bottom, -zNear)
       and (right, top,  -zNear) specify the points on the near clipping plane
       that  are  mapped to the lower left and upper right corners of the win-
       dow, assuming that the eye is located at (0, 0,  0).   -zFar  specifies
       the  location  of  the far clipping plane.  Both zNear and zFar must be
       positive.

       Use ggllPPuusshhMMaattrriixx and ggllPPooppMMaattrriixx to save and restore the current matrix
       stack.

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

                                  r = zFar / zNear

       roughly log2(r) bits of depth buffer precision  are  lost.   Because  r
       approaches  infinity  as zNear approaches 0, zNear must never be set to
       0.

EERRRROORRSS
       GGLLIINNVVAALLIIDDVVAALLUUEE is generated if zNear or zFar is not positive,  or  if
       left = right, or bottom = top.

       GGLLIINNVVAALLIIDDOOPPEERRAATTIIOONN  is generated if ggllFFrruussttuumm is executed between the
       execution of ggllBBeeggiinn and the corresponding execution of ggllEEnndd.

AASSSSOOCCIIAATTEEDD GGEETTSS
       ggllGGeett with argument GGLLMMAATTRRIIXXMMOODDEE
       ggllGGeett with argument GGLLMMOODDEELLVVIIEEWWMMAATTRRIIXX
       ggllGGeett with argument GGLLPPRROOJJEECCTTIIOONNMMAATTRRIIXX
       ggllGGeett with argument GGLLTTEEXXTTUURREEMMAATTRRIIXX
       ggllGGeett with argument GGLLCCOOLLOORRMMAATTRRIIXX

SEE ALSO
       ggllOOrrtthhoo, ggllMMaattrriixxMMooddee, ggllMMuullttMMaattrriixx, ggllPPuusshhMMaattrriixx, ggllVViieewwppoorrtt



                                                                 GLFRUSTUM(3G)