glFrustum

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:

Typically, the matrix mode is GL_PROJECTION , and $\left(\mathit{left},\mathit{bottom},-\mathit{nearVal}\right)$ and $\left(\mathit{right},\mathit{top},-\mathit{nearVal}\right)$ 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). $-\mathit{farVal}$ 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.

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

$\mathit{r}=\frac{\mathit{farVal}}{\mathit{nearVal}}$

roughly ${\mathit{log}}_2\left(\mathit{r}\right)$ bits of depth buffer precision are lost. Because $\mathit{r}$ approaches infinity as nearVal approaches 0, nearVal must never be set to 0.

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 .

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 , glMatrixMode , glMultMatrix , glPushMatrix , glViewport

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/ .