glFrustum - multiply the current matrix by a perspective matrix
void glFrustum( GLdouble left,
GLdouble far_val )
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:
- left, right
- Specify the coordinates for the left and right vertical clipping
- bottom, top
- Specify the coordinates for the bottom and top horizontal clipping
- near_val, far_val
- Specify the distances to the near and far depth clipping planes. Both
distances must be positive.
Typically, the matrix mode is GL_PROJECTION, and
(left, bottom, -near_val) and (right,
top, -near_val) 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). -far_val specifies the
location of the far clipping plane. Both near_val and far_val
must be positive.
Use glPushMatrix and glPopMatrix to save and restore
the current matrix stack.
Depth buffer precision is affected by the values specified for near_val
and far_val. The greater the ratio of far_val to near_val
is, the less effective the depth buffer will be at distinguishing between
surfaces that are near each other. If
bits of depth buffer precision are lost. Because
approaches infinity as near_val approaches 0, near_val must
never be set to 0.
GL_INVALID_VALUE is generated if near_val or far_val 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.
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
glOrtho(3G), glMatrixMode(3G), glMultMatrix(3G),