GLFRUSTUM(3gl)GLFRUSTUM(3gl)NAMEglFrustum - 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.
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:
__________ 0 A 0
0 __________ B 0
⎝ ⎠
0 0 C D
0 0 −1 0
A=__________
B=__________
C=−__________
D=−__________
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=_____
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.
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
SEE ALSO
glOrtho, glMatrixMode, glMultMatrix, glPushMatrix, glViewport
15 Mar 97 GLFRUSTUM(3gl)
