mental ray Architectural and Design Visualization Shader Library

2.5 Detailed Description of Material Parameters 35Using transparent shadowsUsing refractive causticsThe left image shows the result that happen when do refractive caustics is off, the rightthe result when it is on. Both modes can be freely mixed within the same rendering. Photonsare automatically treated accordingly by the built in photon shader, shooting straight throughas direct light in the former case, and being refracted as caustics in the latter.The backface cull switch enables a special mode which makes surfaces completely invisibleto the camera when seen from the reverse side. This is useful to create “magic walls” in aroom. If all walls are created as planes with the normal facing inwards, the backface cullswitch allows the room to be rendered from “outside”. The camera will see into the room,but the walls will still “exist” and cast shadows, bounce photons, etc. while being magically“see through” when the camera steps outside.No Back-face CullingBack-face Culling on the wallsThe propagate alpha switch defines how transparent objects treats any alpha channelinformation in the background. When on, refractions and other transparency effects willpropagate the alpha of the background “through” the transparent object. When off,transparent objects will have an opaque alpha.The no visible area hl parameter concerns the behavior of visible area lights.Keep in mind that traditional “highlights” (i.e. specular effects) is a computer graphics “trick”in place of actually creating a glossy reflection of an actual visible light-emitting surface.