Physically Based Rendering

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## Supplement to the FAR, clause 52.227-7013 (c)(1)(ii), Rights in
## Technical Data and Computer Software.
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#   template: CookTorranceSC.slim
#   author: Scott Eaton
#   description: template for a Cook-Torrance shading component.
#   Supports tutorial on writing a BRDF template in the RenderMan Courseware. 
#   $Revision: 1

slim 1 extensions scotte {
extensions courseware pxsl {		
template shadingcomponent CookTorranceSC {
label cookTorrance
description {
Returns the result of the specular shading operator. Samples
all incoming lights along the specular direction of the surface.
}
parameter float Intensity {
description "Intensity of specular component"
range {0 1 .001}
default .8
detail varying
}
parameter color Color {
description {
Surface specularColor. Use for metallic surfaces
to obtain a filtered highlight color.
}
detail varying
default {1 1 1}
}
parameter float Roughness {
description {
Size or roughness of highlight
}
range {0 1 .001}
default .4
detail varying
}
parameter float IndexOfRefraction {
description {
index of refraction of material
}
range {0 100 .01}
default 1.3
detail varying
}
parameter float gaussianMultiplier {
description {
multiplier for the gaussian microfacet distribution. 
effectively makes the specular highlight brighter. 
}
range {1 500 1}
default 100
detail varying
}
parameter float lightType {
label Use
description {
Whether to respond to traditional CG lights,
lighting from environment maps, or both.
}		    
subtype selector
range {
"Lights" -1
"Environments" 1
"Lights + Environments" 0
}
default 0
}
parameter normal Normal {
detail mustvary "pixar,ShadingNormal"
}
parameter vector ViewDirection {
detail mustvary "pixar,ViewDirection"
display hidden
}

collection shadingcomponent result {
access output
display hidden
parameter color col {
access output
}
eval [::aovOutputParameterMacro]
}
RSLInclude "pxslAOV.h"
RSLSource StaticFunction {
void pxslCookTorranceSC(
float Ks;
color specularColor;
float roughness;
float IOR;
float gaussConstant;
uniform float lightType;
normal Ns;
vector V;
output color col;
DECLARE_AOV_OUTPUT_PARAMS
)
{
INIT_AOV_OUTPUT_PARAMS

#if SLIM_SHADERTYPEID != SLIM_TYPEID_light
extern point P;
normal Nn = normalize(Ns);
vector Vn = normalize(V);
float F, Ktransmit;
float m = roughness;
fresnel( -Vn, Nn, 1/IOR, F, Ktransmit);

color cook = 0;			
if (lightType <= 0)
{
float NdotV = Nn.Vn;
illuminance("-environment", P, Ns, 1.57,
"lightcache", "reuse")
{

float nonspec = 0;
color inshadow = 0, Cl_noshd = 0, Cl_diff;
lightsource("__nonspecular", nonspec);
if (nonspec < 1)
{
vector Ln = normalize(L);
vector H = normalize(Vn+Ln);

float NdotH = Nn.H;
float NdotL = Nn.Ln;
float VdotH = Vn.H;

float alpha = acos(NdotH);
float D = gaussConstant*exp(-(alpha*alpha)/(m*m));
float G = min(1, min((2*NdotH*NdotV/VdotH), (2*NdotH*NdotL/VdotH)));
color k = (1-nonspec)*(F*D*G)/(PI);

if( 0 != lightsource("_shadow", inshadow) )
o_OcclusionDirect += inshadow;
if( 0 == lightsource("_cl_noshadow", Cl_noshd) )
Cl_noshd = Cl;
Cl_diff = Cl_noshd - Cl;
o_SpecularDirect += k * Cl_noshd;
o_SpecularDirectShadow += k * Cl_diff;
}
}
}

// illumination from environments
// unlike diffuse, this (currently) does not contain any
// object-based calculations
if (lightType >= 0)
{
float nonspec = 0;
color envCol = 0;
float cone = 1.55 * pow(roughness,2);
illuminance ("environment", P, Ns, 1.57,
"lightcache", "refresh",
"send:light:__coneangle", cone,
"send:light:__coneaxis", reflect(-V, Ns),
"light:__nonspecular", nonspec)
{
if (nonspec < 1)
{
o_SpecularEnvironment += (1-nonspec) * Cl;
}
}
}

// scale by Ks
color ks = specularColor * Ks;
o_SpecularDirect *= ks;
o_SpecularDirectShadow *= ks;
o_SpecularEnvironment *= ks;
#endif
col = o_SpecularDirect - o_SpecularDirectShadow +
o_SpecularEnvironment;
o_SpecularColor = specularColor;
}
}
}
}
}

Quote:www.garagegames.com/community/blogs/view/22764 is a good starting point for updating the materials.