# MirBSD manpage: gluPerspective(3)

```
GLUPERSPECTIVE(3G)  UNIX Programmer's Manual   GLUPERSPECTIVE(3G)
```

## NAME

```     gluPerspective - set up a perspective projection matrix
```

## C SPECIFICATION

```     void gluPerspective( GLdouble fovy,
GLdouble aspect,
GLdouble zNear,
GLdouble zFar )
```

## PARAMETERS

```     fovy    Specifies the field of view angle, in degrees, in
the y direction.

aspect  Specifies the aspect ratio that determines the field
of view in the x direction. The aspect ratio is the
ratio of x (width) to y (height).

zNear   Specifies the distance from the viewer to the near
clipping plane (always positive).

zFar    Specifies the distance from the viewer to the far
clipping plane (always positive).
```

## DESCRIPTION

```     gluPerspective specifies a viewing frustum into the world
coordinate system. In general, the aspect ratio in
gluPerspective should match the aspect ratio of the associ-
ated viewport. For example, aspect = 2.0 means the viewer's
angle of view is twice as wide in x as it is in y. If the
viewport is twice as wide as it is tall, it displays the
image without distortion.

The matrix generated by gluPerspective is multiplied by the
current matrix, just as if glMultMatrix were called with the
generated matrix. To load the perspective matrix onto the
current matrix stack instead, precede the call to
gluPerspective with a call to glLoadIdentity.

Given f defined as follows:
_o__y_)
f = cotangent( 2

MirBSD #10-current     Printed 2021-12-07                       1

GLUPERSPECTIVE(3G)  UNIX Programmer's Manual   GLUPERSPECTIVE(3G)

The generated matrix is

|
|
|  ______
|  aspect
|    0     0
|          f      0                      |
|    0            0            0         |
|    0     0                   0         |
0  _F__r_±_N__a__                 |
zNear-zFar  _*__F__r__z__e__r_   |
-1       zNear-zFar    |
0         |
|
```

## NOTES

```     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 distin-
guishing between surfaces that are near each other. If
__F__r_
r = zNear

roughly log2r bits of depth buffer precision are lost.
Because r approaches infinity as zNear approaches 0, zNear
must never be set to 0.
```

```     glFrustum(3G), glLoadIdentity(3G), glMultMatrix(3G),