--- ray/doc/ray.1	2011/02/18 00:40:25	1.18
+++ ray/doc/ray.1	2017/04/08 00:09:35	1.31
@@ -1,8 +1,8 @@
-.\" RCSid "$Id"
+.\" RCSid "$Id: ray.1,v 1.31 2017/04/08 00:09:35 greg Exp $"
 .\" Print using the -ms macro package
-.DA 2/17/2011
+.DA 07/10/2016
 .LP
-.tl """Copyright \(co 2011 Regents, University of California
+.tl """Copyright \(co 2016 Regents, University of California
 .sp 2
 .TL
 The
@@ -622,6 +622,21 @@ mod trans2 id
 8 red green blue spec urough vrough trans tspec
 .DE
 .LP
+.UL Ashik2
+.PP
+Ashik2 is the anisotropic reflectance model by Ashikhmin & Shirley.
+The string arguments are the same as for plastic2, but the real
+arguments have additional flexibility to specify the specular color.
+Also, rather than roughness, specular power is used, which has no
+physical meaning other than larger numbers are equivalent to a smoother
+surface.
+.DS
+mod ashik2 id
+4+ ux uy uz funcfile transform
+0
+8 dred dgrn dblu sred sgrn sblu u-power v-power
+.DE
+.LP
 .UL Dielectric
 .PP
 A dielectric material is transparent, and it refracts light
@@ -869,11 +884,10 @@ mod transdata id
 .PP
 The BSDF material type loads an XML (eXtensible Markup Language)
 file describing a bidirectional scattering distribution function.
-
 Real arguments to this material may define additional
 diffuse components that augment the BSDF data.
-String arguments are used to define thickness for hidden
-objects and the "up" orientation for the material.
+String arguments are used to define thickness for proxied
+surfaces and the "up" orientation for the material.
 .DS
 mod BSDF id
 6+ thick BSDFfile ux uy uz funcfile transform
@@ -883,25 +897,25 @@ mod BSDF id
      rbdif gbdif bbdif
      rtdif gtdif btdif
 .DE
-The first string argument is a "thickness" parameter that is useful
-for hiding detail geometry for transmitting systems, e.g.,
-complex fenestration.
-If a view or shadow ray hits a BSDF surface with non-zero specular transmission
-and positive thickness, the ray will pass directly through with no
-reflection or transmission due to the BSDF.
+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.
-In contrast, a scattered ray will use the BSDF transmission,
-offsetting transmitted sample rays by the thickness amount
-to avoid any intervening geometry.
-In this manner, BSDF surfaces may act as simplified stand-ins for detailed
-system geometry, which may still be present and visible in the simulation.
-If the BSDF has back-side reflection data, a parallel surface should be
-specified slightly less than the given thickness away from the front surface
-to enclose the system geometry on both sides.
-A zero thickness implies that the BSDF geomtery is all there is, and
-thickness is ignored if there is no transmitted component, or transmission is
-purely diffuse.
+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).
 .LP
 The second string argument is the name of the BSDF file, which is
 found in the usual auxiliary locations.
@@ -947,8 +961,10 @@ N mod1 mod2 .. modN
 The first modifier will also be used to shade the area leaving the
 antimatter volume and entering the regular volume.
 If mod1 is void, the antimatter volume is completely invisible.
-Antimatter does not work properly with the material type "trans",
-and multiple antimatter surfaces should be disjoint.
+If shading is desired at antimatter surfaces, it is important
+that the related volumes are closed with outward-facing normals.
+Antimatter surfaces should not intersect with other antimatter boundaries,
+and it is unwise to use the same modifier in nested antimatter volumes.
 The viewpoint must be outside all volumes concerned for a correct
 rendering.
 .NH 3
@@ -1156,6 +1172,7 @@ between 0.1 (for tightly spaced characters) and 0.3 (f
 Mixtures
 .PP
 A mixture is a blend of one or more materials or textures and patterns.
+Blended materials should not be light source types or virtual source types.
 The basic types are given below.
 .LP
 .UL Mixfunc
@@ -1552,6 +1569,25 @@ the Ecole Polytechnique Federale de Lausanne (EPFL Uni
 in Lausanne, Switzerland.
 .NH 1
 References
+.LP
+Ward, G., M. Kurt & N. Bonneel,
+``Reducing Anisotropic BSDF Measurement to Common Practice,''
+.I Workshop on Material Appearance Modeling,
+2014.
+.LP
+McNeil, A., C.J. Jonsson, D. Appelfeld, G. Ward, E.S. Lee,
+``A validation of a ray-tracing tool used to generate
+bi-directional scattering distribution functions for
+complex fenestration systems,''
+.I "Solar Energy",
+98, 404-14, November 2013.
+.LP
+Ward, G., R. Mistrick, E.S. Lee, A. McNeil, J. Jonsson,
+``Simulating the Daylight Performance of Complex Fenestration Systems
+Using Bidirectional Scattering Distribution Functions within Radiance,''
+.I "Leukos",
+7(4),
+April 2011.
 .LP
 Cater, K., A. Chalmers, G. Ward,
 ``Detail to Attention: Exploiting Visual Tasks for Selective Rendering,''