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   this work for additional information regarding copyright ownership.
   The ASF licenses this file to You 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,
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   See the License for the specific language governing permissions and
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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:
Vincent Hardy
Version:
$Id: SpotLight.java 1733416 2016-03-03 07:07:13Z gadams $/**
 * 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: SpotLight.java 1733416 2016-03-03 07:07:13Z gadams $
 */
public class SpotLight extends AbstractLight {
    
The light position, in user space
/**
     * The light position, in user space
     */
    private double lightX, lightY, lightZ;

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

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

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

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

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

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

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

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

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

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

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

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

    public SpotLight(double lightX, double lightY, double lightZ,
                     double pointAtX, double pointAtY, double pointAtZ,
                     double specularExponent, double limitingConeAngle,
                     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( Math.toRadians( limitingConeAngle ) );

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

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

        S[0] *= invNorm;
        S[1] *= invNorm;
        S[2] *= invNorm;
    }

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

    
Computes the light vector in (x, y, z)
Params:
x – x-axis coordinate where the light should be computed
y – y-axis coordinate where the light should be computed
z – z-axis coordinate where the light should be computed
L – array of length 3 where the result is stored
Returns:
the intensity factor for this light vector./**
     * 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
     * @return the intensity factor for this light vector.
     */
    public final double getLightBase(final double x, final double y,
                                     final double z,
                                     final double[] L){
        // Light Vector, L
        double L0 = lightX - x;
        double L1 = lightY - y;
        double L2 = lightZ - z;

        final double invNorm = 1.0/Math.sqrt( L0*L0 + L1*L1 + L2*L2 );

        L0 *= invNorm;
        L1 *= invNorm;
        L2 *= invNorm;

        double LS = -(L0*S[0] + L1*S[1] + L2*S[2]);

        // copy the work-variables into return-array
        L[0] = L0;
        L[1] = L1;
        L[2] = L2;

        if(LS <= limitingCos){
            return 0;
        } else {
            double Iatt = limitingCos/LS;
            Iatt *= Iatt;
            Iatt *= Iatt;
            Iatt *= Iatt;
            Iatt *= Iatt;
            Iatt *= Iatt;
            Iatt *= Iatt; // akin Math.pow(Iatt, 64)

            Iatt = 1 - Iatt;
            return Iatt*Math.pow(LS, specularExponent);
        }
    }

    
Computes the light vector in (x, y, z)
Params:
x – x-axis coordinate where the light should be computed
y – y-axis coordinate where the light should be computed
z – z-axis coordinate where the light should be computed
L – array of length 3 where the result is stored,
         x,y,z are scaled by light intensity./**
     * 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,
     *          x,y,z are scaled by light intensity.
     */
    public final void getLight(final double x, final double y,
                               final double z,
                               final double[] L){
        final double s = getLightBase(x, y, z, L);
        L[0] *= s;
        L[1] *= s;
        L[2] *= s;
    }

    
computes light vector in (x, y, z).
Params:
x – x-axis coordinate where the light should be computed
y – y-axis coordinate where the light should be computed
z – z-axis coordinate where the light should be computed
L – array of length 4 where result is stored.
         0,1,2 are x,y,z respectively of light vector (normalized).
         3 is the intensity of the light at this point./**
     * computes 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 4 where result is stored.
     *          0,1,2 are x,y,z respectively of light vector (normalized).
     *          3 is the intensity of the light at this point.
     */
    public final void getLight4(final double x, final double y, final double z,
                               final double[] L){
        L[3] = getLightBase(x, y, z, L);
    }

    public double[][] getLightRow4(double x, double y,
                                  final double dx, final int width,
                                  final double[][] z,
                                  final double[][] lightRow) {
        double [][] ret = lightRow;
        if (ret == null)
            ret = new double[width][4];

        for(int i=0; i<width; i++){
            getLight4(x, y, z[i][3], ret[i]);
            x += dx;
        }

        return ret;
    }

}