GLFRUSTUM(3G)															     GLFRUSTUM(3G)

NAME

       glFrustum - multiply the current matrix by a perspective matrix

C SPECIFICATION

       void glFrustum( GLdouble left,
		       GLdouble right,
		       GLdouble bottom,
		       GLdouble top,
		       GLdouble near_val,
		       GLdouble far_val )

PARAMETERS

       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.

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

DESCRIPTION

       glFrustum  describes  a	perspective matrix that produces a perspective 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:

							      [__________      0     A	0]
								    0	  __________ B	0
								    0	       0     C	D
								    0	       0     -1 0

								      A=__________

								      B=__________

								   C=-________________

								   D=-________________

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

       Use glPushMatrix and glPopMatrix to save and restore the current matrix stack.

NOTES

       Depth buffer precision is affected by the values specified for near_val and far_val.  The greater the ratio of far_val to near_val is,  the
       less effective the depth buffer will be at distinguishing between surfaces that are near each other.  If

								       r=________

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

ERRORS

       GL_INVALID_VALUE is generated if near_val or far_val is not positive, or if left = right, or bottom = top.

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

ASSOCIATED GETS

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

SEE ALSO

       glOrtho(3G), glMatrixMode(3G), glMultMatrix(3G), glPushMatrix(3G), glViewport(3G)

																     GLFRUSTUM(3G)