--- ray/doc/ray.1	2011/02/18 00:40:25	1.18
+++ ray/doc/ray.1	2016/07/10 23:41:37	1.30
@@ -1,8 +1,8 @@
-.\" RCSid "$Id"
+.\" RCSid "$Id: ray.1,v 1.30 2016/07/10 23:41:37 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.
@@ -1156,6 +1170,7 @@ 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 +1567,25 @@ 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,''