`glFrustum`: multiply the current matrix by a perspective matrix.

C Specification |
Parameters |
Description |
Notes |
Errors |
Associated Gets |
See Also
void glFrustum(
GLdouble *left*,
GLdouble *right*,
GLdouble *bottom*,
GLdouble *top*,
GLdouble *zNear*,
GLdouble *zFar*)

*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.

`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:

E |
0 |
A |
0 |

0 |
F |
B |
0 |

0 |
0 |
C |
D |

0 |
0 |
1 |
0 |

where:
- A = (
*right* + *left*) /
(*right* *left*)
- B = (
*top* + *bottom*) /
(*top* *bottom*)
- C = (
*far* + *near*) /
(*far* *near*)
- D = (2
*far**near*) /
(*far* *near*)
- E = (2
*near*) /
(*right* *left*)
- F = (2
*near*) /
(*top* *bottom*)

Typically, the matrix mode is **GL_PROJECTION**, 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 window, 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 `glPushMatrix` and `glPopMatrix` to save and restore the
current matrix stack.

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

roughly log_{2} *r* bits of depth-buffer precision
are lost. Because *r* approaches infinity as *zNear*
approaches 0, *zNear* must never be set to 0.

**GL_INVALID_VALUE** is generated if *zNear* or
*zFar* is not positive.
**GL_INVALID_OPERATION** is generated if `glFrustum` is executed between the
execution of `glBegin` and the
corresponding execution of `glEnd`.

`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`