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.\" RCSid "$Id" |
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.\" Print using the -ms macro package |
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< |
.DA 4/30/2008 |
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.DA 2/17/2011 |
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.LP |
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.tl """Copyright \(co 2008 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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The scattering eccentricity parameter will likewise override the global |
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setting if it is present. |
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Scattering eccentricity indicates how much scattered light favors the |
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forward direction, as fit by the Heyney-Greenstein function: |
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forward direction, as fit by the Henyey-Greenstein function: |
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.DS |
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P(theta) = (1 - g*g) / (1 + g*g - 2*g*cos(theta))^1.5 |
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.DE |
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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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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 proxied |
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surfaces 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 may be used |
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to hide detail geometry being proxied by an aggregate BSDF material. |
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If a view or shadow ray hits a BSDF proxy with non-zero thickness, |
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it will pass directly through as if the surface were not there. |
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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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The BSDF is used when a scattered (indirect) ray hits the surface, |
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and any transmitted sample rays will be offset by the thickness amount |
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to avoid the hidden geometry and gather samples from the other side. |
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In this manner, BSDF surfaces can improve the results for indirect |
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scattering from complex systems without sacrificing appearance or |
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shadow accuracy. |
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If the BSDF has transmission and back-side reflection data, |
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a parallel BSDF surface may be |
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placed slightly less than the given thickness away from the front surface |
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to enclose the complex geometry on both sides. |
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The sign of the thickness is important, as it indicates whether the |
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proxied geometry is behind the BSDF surface (when thickness is positive) |
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or in front (when thickness is negative). |
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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 |
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Antimatter is a material that can "subtract" volumes from other volumes. |
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Pictures may be displayed directly under X11 using the program |
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.I ximage, |
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or converted a standard image format. |
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< |
.I Ra_avs |
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converts to and from AVS image format. |
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.I Ra_pict |
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converts to Macintosh 32-bit PICT2 format. |
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.I Ra_bmp |
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converts to and from Microsoft Bitmap images. |
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.I Ra_ppm |
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converts to and from Poskanzer Portable Pixmap formats. |
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.I Ra_pr |
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converts to and from Sun 8-bit rasterfile format. |
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.I Ra_pr24 |
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converts to and from Sun 24-bit rasterfile format. |
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.I Ra_ps |
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converts to PostScript color and greyscale formats. |
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.I Ra_rgbe |
