@@ -1053,6 +1053,84 @@ unless the line integrals consider enclosed geometry.
+ mod BSDF id + 6+ thick BSDFfile ux uy uz funcfile transform + 0 + 0|3|6|9 + rfdif gfdif bfdif + rbdif gbdif bbdif + rtdif gtdif btdif ++ +
+ The first string argument is a "thickness" parameter that may be used + to hide detail geometry being proxied by an aggregate BSDF material. + If a view or shadow ray hits a BSDF proxy with non-zero thickness, + it will pass directly through as if the surface were not there. + Similar to the illum type, this permits direct viewing and + shadow testing of complex geometry. + The BSDF is used when a scattered (indirect) ray hits the surface, + and any transmitted sample rays will be offset by the thickness amount + to avoid the hidden geometry and gather samples from the other side. + In this manner, BSDF surfaces can improve the results for indirect + scattering from complex systems without sacrificing appearance or + shadow accuracy. + If the BSDF has transmission and back-side reflection data, + a parallel BSDF surface may be + placed slightly less than the given thickness away from the front surface + to enclose the complex geometry on both sides. + The sign of the thickness is important, as it indicates + whether the proxied geometry is behind the BSDF + surface (when thickness is positive) or in front (when + thickness is negative). +
+ The second string argument is the name of the BSDF file, + which is found in the usual auxiliary locations. The + following three string parameters name variables for an + "up" vector, which together with the surface + normal, define the local coordinate system that orients the + BSDF. These variables, along with the thickness, are defined + in a function file given as the next string argument. An + optional transform is used to scale the thickness and + reorient the up vector. +
+ If no real arguments are given, the BSDF is used by itself + to determine reflection and transmission. If there are at + least 3 real arguments, the first triplet is an additional + diffuse reflectance for the front side. At least 6 real + arguments adds diffuse reflectance to the rear side of the + surface. If there are 9 real arguments, the final triplet + will be taken as an additional diffuse transmittance. All + diffuse components as well as the non-diffuse transmission + are modified by patterns applied to this material. The + non-diffuse reflection from either side are unaffected. + Textures perturb the effective surface normal in the usual + way. +
+ The surface normal of this type is not altered to face the + incoming ray, so the front and back BSDF reflections may + differ. (Transmission is identical front-to-back by physical + law.) If back visibility is turned off during rendering and + there is no transmission or back-side reflection, only then + the surface will be invisible from behind. Unlike other + data-driven material types, the BSDF type is fully supported + and all parts of the distribution are properly sampled. +
+ +