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```glFrustum(3)                                                    glFrustum(3)

```

## NAME

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

```

## C SPECIFICATION

```       void glFrustum( GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble zNear,
GLdouble zFar )

```

## 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.

zNear, zFar 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 zNear
------------       0              A              0
right - left

2 zNear
0         ------------        B              0
top - bottom

0              0              C              D

0              0              -1             0

A = (right + left) / (right - left)

B = (top + bottom) / (top - bottom)

C = - (zFar + zNear) / (zFar - zNear)

D = - (2 zFar zNear) / (zFar - zNear)

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 win-
dow, 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.

```

## 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  effec-
tive  the  depth buffer will be at distinguishing between surfaces that
are near each other.  If

r = zFar / zNear

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

```

## ERRORS

```       GL_INVALID_VALUE is generated if zNear or zFar 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

```

```       glOrtho(3), glMatrixMode(3), glMultMatrix(3), glPushMatrix(3),
```© manpagez.com 2000-2023