Smoothing does add a level of complexity since backface culling is mainly restricted to flat, unaltered polygons, but in the display and render engine, this should be done prior to smoothing (or other polygon interpolations, such as Phong et al). The basic process is: 1. Transform objects into world space (build the scene) 2. Transform into view space (build the camera view) 3. Object level cull (stuff outside of view frustrum) 4. Backface cull remaining objects 5. Clip remaining stuff against view frustrum 6. Project onto view plane (convert 3D pts into 2D) 7. Render If their smoothing is being done before step 4., that could cause some grief. Question is how smoothing is implemented. If it involves polygon subdivision, then backface culling still works in either case. If it's a form of Phong interpolation, it should really occur at step 7.. One would hope that they do smoothing only during step 7. (?). BYS