Method GL.glFrustum()

Method glFrustum

void glFrustum(float left, float right, float bottom, float top, float nearVal, float farVal)

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:

[

2nearVal/right-left	0	A	0
0	2nearVal/top-bottom	B	0
0	0	C	D
0	0	-1	0

]

A=right+left/right-left

B=top+bottom/top-bottom

C=-farVal+nearVal/farVal-nearVal

D=-2farValnearVal/farVal-nearVal

Typically, the matrix mode is GL_PROJECTION, and (left, bottom, -nearVal) and (right, top, -nearVal) 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). -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.

Parameter left

Parameter right

Specify the coordinates for the left and right vertical clipping planes.

Parameter bottom

Parameter top

Specify the coordinates for the bottom and top horizontal clipping planes.

Parameter nearVal

Parameter farVal

Specify the distances to the near and far depth clipping planes. Both distances must be positive.

Throws

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.

Note

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

r=farVal/nearVal

roughly log₂(r) bits of depth buffer precision are lost. Because r approaches infinity as nearVal approaches 0, nearVal must never be set to 0.