F
glFrustum
Chapter 6
159
glFrustum
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:
E0A0
0FB0
00CD
0 0 -1 0
where:
A = (right + left) / (right - left)
B = (top + bottom) / (top - bottom)
C = (far + near) / (far- near)
D = (2×far×near) / (far- near)
E = (2×near) / (right - left)
F = (2×near) / (top - bottom)
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 window, 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.
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