glFrustum(3G) OpenGL Reference glFrustum(3G)NAME
glFrustum - multiply the current matrix by a perspective matrix
C SPECIFICATION
void glFrustum( GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble near,
GLdouble far )
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.
near, far 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:
| |
| |
| |
| ____________ |
0 A 0
| right - left |
| |
____________
| 0 B 0 |
top - bottom
| |
| 0 0 C D |
| |
0 0 -1 0
____________
A =
right - left
____________
B =
top - bottom
__________
C = -
far - near
__________
D = -
far - near
Typically, the matrix mode is GL_PROJECTION, and (left, bottom, -near)
and (right, top, -near) specify the points on the near clipping plane
that are mapped to the lower left and upper right corners of the window,
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glFrustum(3G) OpenGL Reference glFrustum(3G)
assuming that the eye is located at (0, 0, 0). -far specifies the
location of the far clipping plane. Both near and far 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 near and
far. The greater the ratio of far to near is, the less effective the
depth buffer will be at distinguishing between surfaces that are near
each other. If
____
r =
near
roughly log (r) bits of depth buffer precision are lost. Because r
2
approaches infinity as near approaches 0, near must never be set to 0.
ERRORS
GL_INVALID_VALUE is generated if near or far 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 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
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