Autodesk 12812-051462-9011 User Guide 3 - Page 981

■ The mental ray renderer assumes that all directional lights come from infinity, so objects that are behind the direct light object in the 3ds Max scene will also be illuminated. Ray Tracing The mental ray ray tracer is fast and provides excellent quality images, but it's important to use it correctly. The mental ray renderer does not fully support cubic maps for Reflect/Refract maps on page 5964. It uses them if they have already been generated by the default scanline renderer, but it does not generate them. If Source > From File is active and the mental ray renderer can find the six cubic maps, it uses them. If Source > Automatic is active, or if the cubic maps cannot be found, the mental ray renderer generates ray-traced reflections or refractions instead. Ray Tracing Setup On the rendering menu, Ray Tracer Settings and Raytrace Global Include/Exclude are disabled while the mental ray renderer is active. These controls adjust ray-trace settings for the scanline renderer only. The settings of these controls have no impact on the mental ray renderer. The ray-tracing controls for mental ray appear on the Renderer panel > Rendering Algorithms rollout on page 6277. TIP While the mental ray renderer ignores the global inclusion or exclusion settings for the ray tracer, you can enable or disable ray-tracing at the local level of a Raytrace material or map. Ray Tracing Rules of Thumb Say you're rendering a (lathed) wineglass, with an inner and outer surface and a piece of geometry representing the wine. The wine geometry is just slightly smaller than the inner surfaces of the wineglass, and capped with a flat top. Now, you go to render the glass. After rendering the scene, however, there's something wrong: the inner surfaces of the glass don't seem reflective enough, and the wine isn't refracting properly. What's wrong? It's possible that you have the number of reflections and refractions set too low for the number of surfaces you have. To check this, go to the Renderer panel > Rendering Algorithms rollout on page 6277 and look at the Maximum Trace Depth settings. If you haven't changed the parameters, then you should see Max. Reflections and Max. Refractions set to the default of 6, and Max. Depth set to 6. 6236 | Chapter 20 Rendering