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.\" RCSid "$Id" |
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.\" Print using the -ms macro package |
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< |
.DA 3/12/2010 |
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.DA 2/17/2011 |
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.LP |
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< |
.tl """Copyright \(co 2010 Regents, University of California |
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.tl """Copyright \(co 2011 Regents, University of California |
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.sp 2 |
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.TL |
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The |
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0 |
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6+ red green blue rspec trans tspec A7 .. |
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.DE |
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.LP |
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.UL BSDF |
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.PP |
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The BSDF material type loads an XML (eXtensible Markup Language) |
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file describing a bidirectional scattering distribution function. |
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|
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Real arguments to this material may define additional |
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diffuse components that augment the BSDF data. |
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String arguments are used to define thickness for hidden |
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objects and the "up" orientation for the material. |
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.DS |
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mod BSDF id |
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6+ thick BSDFfile ux uy uz funcfile transform |
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0 |
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0|3|6|9 |
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rfdif gfdif bfdif |
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rbdif gbdif bbdif |
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rtdif gtdif btdif |
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.DE |
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The first string argument is a "thickness" parameter that is useful |
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for hiding detail geometry for transmitting systems, e.g., |
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complex fenestration. |
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If a view or shadow ray hits a BSDF surface with non-zero specular transmission |
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and positive thickness, the ray will pass directly through with no |
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reflection or transmission due to the BSDF. |
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Similar to the illum type, this permits direct viewing and |
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shadow testing of complex geometry. |
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In contrast, a scattered ray will use the BSDF transmission, |
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offsetting transmitted sample rays by the thickness amount |
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to avoid any intervening geometry. |
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In this manner, BSDF surfaces may act as simplified stand-ins for detailed |
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system geometry, which may still be present and visible in the simulation. |
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If the BSDF has back-side reflection data, a parallel surface should be |
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specified slightly less than the given thickness away from the front surface |
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to enclose the system geometry on both sides. |
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A zero thickness implies that the BSDF geomtery is all there is, and |
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thickness is ignored if there is no transmitted component, or transmission is |
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purely diffuse. |
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.LP |
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The second string argument is the name of the BSDF file, which is |
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found in the usual auxiliary locations. |
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The following three string parameters name variables for an "up" vector, |
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which together with the surface normal, define the |
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local coordinate system that orients the BSDF. |
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These variables, along with the thickness, are defined in a function |
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file given as the next string argument. |
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An optional transform is used to scale the thickness and reorient the up vector. |
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.LP |
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If no real arguments are given, the BSDF is used by itself to determine |
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reflection and transmission. |
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If there are at least 3 real arguments, the first triplet is an |
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additional diffuse reflectance for the front side. |
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At least 6 real arguments adds diffuse reflectance to the rear side of the surface. |
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If there are 9 real arguments, the final triplet will be taken as an additional |
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diffuse transmittance. |
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All diffuse components as well as the non-diffuse transmission are |
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modified by patterns applied to this material. |
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The non-diffuse reflection from either side are unaffected. |
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Textures perturb the effective surface normal in the usual way. |
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.LP |
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The surface normal of this type is not altered to face the incoming ray, |
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so the front and back BSDF reflections may differ. |
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(Transmission is identical front-to-back by physical law.)\0 |
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If back visibility is turned off during rendering and there is no |
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transmission or back-side reflection, only then the surface will be |
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invisible from behind. |
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Unlike other data-driven material types, the BSDF type is fully |
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supported and all parts of the distribution are properly sampled. |
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.LP |
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.UL Antimatter |
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.PP |
