HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 159

Chapter 6 F glFrustum glFrustum glFrustum: multiply the current matrix by a perspective matrix. C Specification void glFrustum( GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble zNear, GLdouble zFar) Parameters left, right bottom, top zNear, zFar Specify the coordinates for the left and right vertical clipping planes. Specify the coordinates for the bottom and top horizontal clipping planes. 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: E0A0 0 FB 0 0 0C D 0 0 -1 0 where: A = (right + left) / (right - left) B = (top + bottom) / (top - bottom) C = (far + near) / (far- near) D = (2×far×near) / (far- near) E = (2×near) / (right - left) F = (2×near) / (top - bottom) 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. 159