 OpenGL man pages

```

```

## Name

```  glFrustum - multiply the current matrix by a perspective matrix

```

## C Specification

```  void glFrustum( GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble near,
GLdouble far )

```

## 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,	far   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.  (left, bottom, -near) and (right, top,  -near) 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).	 -far specifies	the location of	the far	clipping
plane.  Both near and	far must be positive.  The corresponding matrix	is

|					   |
|    2·near  			   |
|  ----------                           |
|  right-left       0       A       0   |
|					   |
|	  0	    2·near     B       0   |
|              ----------               |
|		  top-bottom		   |
|	  0	       0       C       D   |
|					   |
|	  0	       0       -1      0   |

right+left
A = ----------
right-left

top+bottom
B = ----------
top-bottom

far+near
C = - --------
far-near

2·far·near
D = - ----------
far-near

The current matrix is	multiplied by this matrix with the result replacing
the current matrix.  That is,	if M is	the current matrix and F is the
frustum perspective matrix, then M is	replaced with M·F.

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

```

## Notes

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

far
r = ----
near

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

```

## Errors

```  GL_INVALID_VALUE is generated	if near	or far is not positive.

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

```

```  glOrtho, glMatrixMode, glMultMatrix, glPushMatrix, glViewport