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GLFRUSTUM(3G)			 OpenGL Manual			 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 nearVal, GLdouble farVal);

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.

       nearVal, farVal
	   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:

       2 ⁢ nearVal right - left 0 A 0 0 2 ⁢ nearVal top - bottom B 0 0 0 C D 0
       0 -1 0

       A = right + left right - left

       B = top + bottom top - bottom

       C = - farVal + nearVal farVal - nearVal

       D = - 2 ⁢ farVal ⁢ nearVal farVal - nearVal

       Typically, the matrix mode is GL_PROJECTION, and left bottom - nearVal
       and right top - nearVal 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).  - farVal
       specifies the location of the far clipping plane. Both nearVal and
       farVal 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 nearVal
       and farVal. The greater the ratio of farVal to nearVal is, the less
       effective the depth buffer will be at distinguishing between surfaces
       that are near each other. If

       r = farVal nearVal

       roughly log 2 ⁡ r bits of depth buffer precision are lost. Because r
       approaches infinity as nearVal approaches 0, nearVal must never be set
       to 0.

ERRORS
       GL_INVALID_VALUE is generated if nearVal or farVal is not positive, or
       if left = right, or bottom = top, or near = far.

       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(), glMatrixMode(), glMultMatrix(), glPushMatrix(), glViewport()

COPYRIGHT
       Copyright © 1991-2006 Silicon Graphics, Inc. This document is licensed
       under the SGI Free Software B License. For details, see
       http://oss.sgi.com/projects/FreeB/.

AUTHORS
       opengl.org

opengl.org			  03/16/2013			 GLFRUSTUM(3G)

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