glFrustum  4O0ZZIL

[New - Windows 95, OEM Service Release 2]

The glFrustum function multiplies the current matrix by a perspective matrix.

void glFrustum(

Parameters

left, right

The coordinates for the left and right vertical clipping planes.

bottom, top

The coordinates for the bottom and top horizontal clipping planes.

znear, zfar

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

Remarks

The glFrustum function describes a perspective matrix that produces a perspective projection. The (left, bottom, znear) and (right, top, znear) parameters specify the points on the near clipping plane that are mapped to the lower-left and upper-right corners of the window, respectively, assuming that the eye is located at (0, 0, 0). The zfar parameter specifies the location of the far clipping plane. Both znear and zfar must be positive. The corresponding matrix is:

{bml bm25.BMP}

{bml bm26.BMP}

The glFrustum function multiplies the current matrix by this matrix, with the result replacing the current matrix. That is, if M is the current matrix and F is the frustum perspective matrix, then glFrustum replaces M with M   F.

Use glPushMatrix1MYNI2H and glPopMatrix1MYNI2H to save and restore the current matrix stack.

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

{bml bm27.BMP}

roughly log (2)  r bits of depth buffer precision are lost. Because r approaches infinity as znear approaches zero, you should never set znear to zero.

The following functions retrieve information about glFrustum:

glGet8KNKTW with argument GL_MATRIX_MODE

glGet with argument GL_MODELVIEW_MATRIX

glGet with argument GL_PROJECTION_MATRIX

glGet with argument GL_TEXTURE_MATRIX

Error Codes

The following are the error codes generated and their conditions.

See Also