* Java Modular Image Synthesis Toolkit (JMIST)

* Copyright (C) 2008-2013 Bradley W. Kimmel

*

* Permission is hereby granted, free of charge, to any person

* obtaining a copy of this software and associated documentation

* files (the "Software"), to deal in the Software without

* restriction, including without limitation the rights to use,

* copy, modify, merge, publish, distribute, sublicense, and/or sell

* copies of the Software, and to permit persons to whom the

* Software is furnished to do so, subject to the following

* conditions:

*

* The above copyright notice and this permission notice shall be

* included in all copies or substantial portions of the Software.

*

* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,

* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES

* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND

* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT

* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,

* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR

* OTHER DEALINGS IN THE SOFTWARE.

*/

* @author Brad

*

*/

  /** Serialization version ID. */

  private static final long serialVersionUID = 58334131261636901L;

  private final Painter diffuse;

  private final Painter specular;

  private final double alpha;

  /**

   *

   * @param diffuse

   * @param specular

   * @param alpha

   */

  public IsotropicWardMaterial(Painter diffuse, Painter specular, double alpha) {

    this.diffuse = diffuse;

    this.specular = specular;

    this.alpha = alpha;

  }

  /**

   *

   * @param diffuse

   * @param specular

   * @param alpha

   */

  public IsotropicWardMaterial(Spectrum diffuse, Spectrum specular, double alpha) {

    this(new UniformPainter(diffuse), new UniformPainter(specular), alpha);

  }

  /* (non-Javadoc)

   * @see ca.eandb.jmist.framework.material.AbstractMaterial#bsdf(ca.eandb.jmist.framework.SurfacePoint, ca.eandb.jmist.math.Vector3, ca.eandb.jmist.math.Vector3, ca.eandb.jmist.framework.color.WavelengthPacket)

   */

  @Override

  public Color bsdf(SurfacePoint x, Vector3 in, Vector3 out,

      WavelengthPacket lambda) {

    Vector3 N = x.getNormal();

    if (-N.dot(in) <= 0.0 || N.dot(out) <= 0.0) {

      return lambda.getColorModel().getBlack(lambda);

    }

    in = in.unit();

    out = out.unit();

    Color d = diffuse.getColor(x, lambda);

    Color s = specular.getColor(x, lambda);

    Vector3 n = x.getShadingNormal();

    Color D = d.divide(Math.PI);

    double ci = -n.dot(in);

    double co = n.dot(out);

    Vector3 h = out.minus(in).unit();

    double ch = n.dot(h);

    double ch2 = ch * ch;

    double sh2 = 1.0 - ch2;

    double th2 = sh2 / ch2;

    double alpha2 = alpha * alpha;

    double k = (1.0 / Math.sqrt(co * ci))

        * Math.exp(-th2 / alpha2) / (4.0 * Math.PI * alpha2);

    Color S = s.times(k);

    return D.plus(S);

  }

  /* (non-Javadoc)

   * @see ca.eandb.jmist.framework.material.AbstractMaterial#getScatteringPDF(ca.eandb.jmist.framework.SurfacePoint, ca.eandb.jmist.math.Vector3, ca.eandb.jmist.math.Vector3, boolean, ca.eandb.jmist.framework.color.WavelengthPacket)

   */

  @Override

  public double getScatteringPDF(SurfacePoint x, Vector3 in, Vector3 out,

      boolean adjoint, WavelengthPacket lambda) {

    Vector3 N = x.getNormal();

    if (-N.dot(in) <= 0.0 || N.dot(out) <= 0.0) {

      return 0.0;

    }

    in = in.unit();

    out = out.unit();

    double d = ColorUtil.getMeanChannelValue(diffuse.getColor(x, lambda));

    double s = ColorUtil.getMeanChannelValue(specular.getColor(x, lambda));

    double total = d + s;

    Vector3 n = x.getShadingNormal();

    double D = d / Math.PI;

    double ci = -n.dot(in);

    double co = n.dot(out);

    Vector3 h = out.minus(in).unit();

    double ch = n.dot(h);

    double ch2 = ch * ch;

    double sh2 = 1.0 - ch2;

    double th2 = sh2 / ch2;

    double alpha2 = alpha * alpha;

    double k = (1.0 / Math.sqrt(co * ci))

        * Math.exp(-th2 / alpha2) / (4.0 * Math.PI * alpha2);

    double S = s * k;

    if (D < 0 || S < 0) {

      throw new RuntimeException("crap");

    }

    return (D + S) / total;

  }

  /* (non-Javadoc)

   * @see ca.eandb.jmist.framework.material.AbstractMaterial#scatter(ca.eandb.jmist.framework.SurfacePoint, ca.eandb.jmist.math.Vector3, boolean, ca.eandb.jmist.framework.color.WavelengthPacket, ca.eandb.jmist.framework.Random)

   */

  @Override

  public ScatteredRay scatter(SurfacePoint x, Vector3 v, boolean adjoint,

      WavelengthPacket lambda, double ru, double rv, double rj) {

    Vector3 n = x.getNormal();

    if (n.dot(v) > 0.0) {

      return null;

    }

    Color d = diffuse.getColor(x, lambda);

    Color s = specular.getColor(x, lambda);

    double davg = ColorUtil.getMeanChannelValue(d);

    double savg = ColorUtil.getMeanChannelValue(s);

    double total = davg + savg;

    Basis3 basis = x.getShadingBasis();

    Vector3 out;

    if (RandomUtil.bernoulli(davg / total, rj)) { // diffuse

      do {

        out = RandomUtil.diffuse(ru, rv).toCartesian(basis);

      } while (n.dot(out) <= 0.0);

    } else { // specular

      do {

        SphericalCoordinates sc = new SphericalCoordinates(

            Math.atan(alpha * Math.sqrt(-Math.log(1.0 - ru))),

            2.0 * Math.PI * rv);

        Vector3 h = sc.toCartesian(basis);

        out = Optics.reflect(v, h);

      } while (n.dot(out) <= 0.0);

    }

    Ray3 ray = new Ray3(x.getPosition(), out);

    double pdf = getScatteringPDF(x, v, out, true, lambda);

    Color value = bsdf(x, v, out, lambda).divide(pdf);

    return ScatteredRay.diffuse(ray, value, pdf);

  }

}