void glFrustum | ( | GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble zNear, GLdouble zFar); |
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:
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.
Use glPushMatrix and glPopMatrix 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
GL_INVALID_VALUE is generated if zNear or zFar 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.