sources/org/apache/batik/ext/awt/image/SpotLight.java

/*

   Copyright 2001  The Apache Software Foundation 

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */
package org.apache.batik.ext.awt.image;

import java.awt.Color;

/**
 * A light source which emits a light of constant intensity in all directions.
 *
 * @author <a href="mailto:vincent.hardy@eng.sun.com">Vincent Hardy</a>
 * @version $Id$
 */
public class SpotLight extends AbstractLight {
    /**
     * The light position, in user space
     */
    private double lightX, lightY, lightZ;

    /**
     * Point where the light points to
     */
    private double pointAtX, pointAtY, pointAtZ;

    /**
     * Specular exponent (light focus)
     */
    private double specularExponent;

    /**
     * Limiting cone angle
     */
    private double limitingConeAngle, limitingCos;

    /**
     * Light direction vector
     */
    private final double[] S = new double[3];

    /**
     * @return the light's x position
     */
    public double getLightX(){
        return lightX;
    }

    /**
     * @return the light's y position
     */
    public double getLightY(){
        return lightY;
    }

    /**
     * @return the light's z position
     */
    public double getLightZ(){
        return lightZ;
    }

    /**
     * @return x-axis coordinate where the light points to
     */
    public double getPointAtX(){
        return pointAtX;
    }

    /**
     * @return y-axis coordinate where the light points to
     */
    public double getPointAtY(){
        return pointAtY;
    }

    /**
     * @return z-axis coordinate where the light points to
     */
    public double getPointAtZ(){
        return pointAtZ;
    }

    /**
     * @return light's specular exponent (focus)
     */
    public double getSpecularExponent(){
        return specularExponent;
    }

    /**
     * @return light's limiting cone angle
     */
    public double getLimitingConeAngle(){
        return limitingConeAngle;
    }

    public SpotLight(final double lightX, final double lightY, final double lightZ,
                     final double pointAtX, final double pointAtY, final double pointAtZ,
                     final double specularExponent, final double limitingConeAngle,
                     final Color lightColor){
        super(lightColor);

        this.lightX = lightX;
        this.lightY = lightY;
        this.lightZ = lightZ;
        this.pointAtX = pointAtX;
        this.pointAtY = pointAtY;
        this.pointAtZ = pointAtZ;
        this.specularExponent = specularExponent;
        this.limitingConeAngle = limitingConeAngle;
        this.limitingCos = Math.cos(limitingConeAngle*Math.PI/180.);

        S[0] = pointAtX - lightX;
        S[1] = pointAtY - lightY;
        S[2] = pointAtZ - lightZ;

        double norm = Math.sqrt(S[0]*S[0]
                                + S[1]*S[1]
                                + S[2]*S[2]);

        S[0] /= norm;
        S[1] /= norm;
        S[2] /= norm;
    }

    /**
     * @return true if the light is constant over the whole surface
     */
    public boolean isConstant(){
        return false;
    }

    /**
     * Computes the light vector in (x, y, z)
     *
     * @param x x-axis coordinate where the light should be computed
     * @param y y-axis coordinate where the light should be computed
     * @param z z-axis coordinate where the light should be computed
     * @param L array of length 3 where the result is stored
     */
    public final void getLight(final double x, final double y, final double z,
                               final double L[]){
        // Light Vector, L
        L[0] = lightX - x;
        L[1] = lightY - y;
        L[2] = lightZ - z;

        final double norm = Math.sqrt(L[0]*L[0] +
                                      L[1]*L[1] +
                                      L[2]*L[2]);

        L[0] /= norm;
        L[1] /= norm;
        L[2] /= norm;
        
        double LS = -(L[0]*S[0] + L[1]*S[1] + L[2]*S[2]);
        
        if(LS > limitingCos){
            double Iatt = limitingCos/LS;
            Iatt *= Iatt;
            Iatt *= Iatt;
            Iatt *= Iatt;
            Iatt *= Iatt;
            Iatt *= Iatt;
            Iatt *= Iatt; // akin Math.pow(Iatt, 64)

            Iatt = 1 - Iatt;
            LS = Iatt*Math.pow(LS, specularExponent);
            
            L[0] *= LS;
            L[1] *= LS;
            L[2] *= LS;
        }
        else{
            L[0] = 0;
            L[1] = 0;
            L[2] = 0;
        }
    }
}