/* 
 * ashshir.sl
 * Simple surface using Ashikmin-Shirley BRDF
 * Peter Stuart
 * $Id: ashshir.sl,v 1.4 2003/05/05 05:22:41 ophi Exp $
 * description: Ashikmin and Shirley BRDF lighting model as described
 * in "An Anisotropic Phong Light Reflection Model." Most of the work
 * is done in ashShirModel.h by two functions - one for dealing with
 * direct lighting, and the other for dealing with environment lighting.
 *
 * ---- surface parameters ----------
 * rd: diffuse reflectance
 * rs: specular reflectance
 * nu: specular exponent along xdir
 * nv: specular exponent perpendicular to xdir
 * refl: amount of reflection to use
 * envname: name of environment map to use. If this is "" the shader will
 *   try to raytrace the environment if there are samples (envsamp > 0)
 * envsamp: number of samples to use when sampling the environment
*/

#include "ashshirModel.h"

surface ashshir (float rd = 0.5, rs = 0.5; float nu = 10, nv = 10;
		 float refl = 0.1; uniform string envname="";
		 uniform float envsamp = 1;)
{
  normal Nf = normalize(faceforward(N,I));
  vector V = normalize(-I);
  vector xdir = normalize(dPdu);

  // contribution from light sources
  Ci = LocIllumAshShir(Nf, V, xdir, rd, rs, nu, nv);

  // contribution from environment
  if (envsamp > 0)
    Ci += refl*EnvIllumAshShir(Nf, V, xdir, rd, rs, nu, nv, envsamp, envname);

  Ci *= Cs;
}