HP Workstation zx2000 OpenGL 1.1 Reference for HP-UX 11.x - Page 160

F glFrustum Use glPushMatrix and glPopMatrix to save and restore the current matrix stack. Notes 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 r = zFar / zNear roughly log2 r bits of depth-buffer precision are lost. Because r approaches infinity as zNear approaches 0, zNear must never be set to 0. Errors • GL_INVALID_VALUE is generated if zNear or zFar is not positive. • GL_INVALID_OPERATION is generated if glFrustum is executed between the execution of glBegin and the corresponding execution of glEnd. Associated Gets glGet with argument GL_MATRIX_MODE glGet with argument GL_MODELVIEW_MATRIX glGet with argument GL_PROJECTION_MATRIX glGet with argument GL_TEXTURE_MATRIX See Also glOrtho, glMatrixMode, glMultMatrix, glPushMatrix glViewport 160 Chapter 6