glFrustum(3G)glFrustum(3G)NAMEglFrustum - multiply the current matrix by a perspective matrix
SYNOPSIS
void glFrustum(
GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble zNear,
GLdouble zFar );
PARAMETERS
Specify the coordinates for the left and right vertical clipping
planes. Specify the coordinates for the bottom and top horizontal
clipping planes. Specify the distances to the near and far depth clip‐
ping planes. Both distances must be positive.
DESCRIPTIONglFrustum() 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 glMultMa‐
trix() were called with the following matrix as its argument: {2 zNear}
/ {right - left} 0 A 0
0 {2 zNear} / {top - bottom} B
0
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 posi‐
tive.
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 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.
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 GETSglGet() 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 ALSOglOrtho(3), glMatrixMode(3), glMultMatrix(3), glPushMatrix(3), glView‐
port(3)glFrustum(3G)