Chapter 5: 3Delight and RenderMan
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# marble reduced scattering + absorption parameters Attribute "subsurface" "color scattering" [2.19 2.62 3.00] "absorption" [0.0021 0.0041 0.0071]
Attribute "subsurface" "color meanfreepath" Attribute "subsurface" "color reflectance" Another way to specify subsurface parameters, using translucency and reflectance (mean free path and diffuse reflectance). These two parameters should be specified in pair. If “reflectance” is not specified it is set to the RiColor of the surface. # marble reduced meanfreepath + diffuse reflectance Attribute "subsurface" "meanfreepath" [8.50 5.566 3.951] "reflectance" [ 0.83 0.79 0.75]
Attribute "subsurface" "refractionindex" This attribute specifies the third parameter of the subsurface simulation. It is a single float indicating the relative index of refraction of the simulated material (commonly referred to as n). Attribute "subsurface" "scale" [1] The values for subsurface scattering use a millimeter scale. Since most scenes are modeled on a different scale, this attribute compensates for that instead of adjusting the parameters themselves. It is a single float which defaults to 1.0. Attribute "subsurface" "shadingrate" [1] This attribute controls how many irradiance samples should be taken during the precomputation phase. It is a single float which defaults to 1.0 and has a meaning similar to RiShadingRate. Attribute "subsurface" "referencecamera" ["cameraname"] Specifies a dicing camera to use when evaluating the subsurface light transport. The camera must be declared with RiCamera first as explained in Section 7.11 [Dicing Cameras], page 153. More on subsurface scattering in Section 7.4.5 [Subsurface Scattering], page 137.
5.2.5 Displacement Whenever a displacement shader is applied to a primitive, one must specify a displacement bound to inform the renderer about maximum displacement amplitude. This is done using one of the attributes described below. Attribute "displacementbound" "float sphere" [radius ] "string coordinatesystem" "ss-name " This tells the renderer that a displaced point does not move outside a sphere of a given radius in the given coordinate system. The following coordinate systems are supported: • "surface" which is the surface shader’s coordinate system. • "displacement" which is the displacement shader’s coordinate system. • "shader" which means "displacement" if a displacement shader is attached to the object and "surface" if not.