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

bottom, top

nearVal, farVal

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