content: // ===============================================================================
  // Authors: AFRL/RQQD
  // Organization: Air Force Research Laboratory, Aerospace Systems Directorate, Power and Control Division
  // 
  // Copyright (c) 2017 Government of the United State of America, as represented by
  // the Secretary of the Air Force.  No copyright is claimed in the United States under
  // Title 17, U.S. Code.  All Other Rights Reserved.
  // ===============================================================================
  
  /*
   * GRAL: GRAphing Library for Java(R)
   *
   * (C) Copyright 2009-2013 Erich Seifert <dev[at]erichseifert.de>,
   * Michael Seifert <mseifert[at]error-reports.org>
   *
   * This file is part of GRAL.
   *
   * GRAL is free software: you can redistribute it and/or modify
   * it under the terms of the GNU Lesser General Public License as published by
   * the Free Software Foundation, either version 3 of the License, or
   * (at your option) any later version.
   *
   * GRAL is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public License
   * along with GRAL.  If not, see <http://www.gnu.org/licenses/>.
   */
  package de.erichseifert.gral.plots.colors;
  
  import java.awt.Color;
  import java.awt.Paint;
  import java.util.Iterator;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.Random;
  
  import de.erichseifert.gral.util.MathUtils;
  
  /**
   * Class that generates pseudo-random colors for specified index values.
   */
  public class RandomColors extends IndexedColorMapper {
  	/** Version id for serialization. */
  	private static final long serialVersionUID = -4518470000665474457L;
  
  	/** Number of comparisons that will be done before accepting two similar
  	random values. */
  	private static final int NUM_COMPARISONS = 4;
  	/** Minimal distance the causes a random values to be to re-generated. */
  	private static final double MIN_DIST = 0.3;
  
  	/** Cache for colors that have already been generated. */
  	private final Map<Integer, Color> colorCache;
  	/** Object for generating random values. */
  	private final Random random;
  	/** Variance settings for hue, saturation and brightness. */
  	//FIXME duplicate code! See QuasiRandomColors
  	private final float[] colorVariance;
  
  	/**
  	 * Creates a new RandomColors object with default seed.
  	 */
  	public RandomColors() {
  		random = new Random();
  		colorCache = new LinkedHashMap<Integer, Color>();
  		colorVariance = new float[] {
  			0.00f, 1.00f,  // Hue
  			0.75f, 0.25f,  // Saturation
  			0.25f, 0.75f   // Brightness
  		};
  	}
  
  	/**
  	 * Creates a new instances with the specified seed.
  	 * @param seed Random number seed.
  	 */
  	public RandomColors(long seed) {
  		this();
  		random.setSeed(seed);
  	}
  
  	/**
  	 * Returns the Paint associated to the specified index value.
  	 * @param index Numeric index.
  	 * @return Paint.
  	 */
  	@Override
  	public Paint get(int index) {
  		Integer key = Integer.valueOf(index);
  		if (colorCache.containsKey(key)) {
  			return colorCache.get(key);
  		}
  
  		// Use the same random numbers for the same input value
  		//long seed = Double.doubleToRawLongBits(value);
  		//random.setSeed(seed);
  
  		// Generate a new color that is distant enough from previous colors
  		boolean match = false;
  		Color r;
  		do {
  			r = getRandomColor();
  			match = true;
  			Iterator<Color> colors = colorCache.values().iterator();
  			for (int i=0; i<NUM_COMPARISONS && colors.hasNext(); i++) {
  				Color prev = colors.next();
  				if (distanceSq(r, prev) < MIN_DIST*MIN_DIST) {
  					match = false;
  					break;
  				}
  			}
  		} while (!match);
  
  		// Remember previous colors to avoid similarities
  		colorCache.put(key, r);
  
  		return r;
  	}
  
  	/**
  	 * Generates a random color with the current color variance.
  	 * @return Color.
  	 */
  	private Color getRandomColor() {
  		float[] colorVariance = getColorVariance();
  		float hue = colorVariance[0] + colorVariance[1]*random.nextFloat();
  		float saturation = colorVariance[2] + colorVariance[3]*random.nextFloat();
  		float brightness = colorVariance[4] + colorVariance[5]*random.nextFloat();
  		return Color.getHSBColor(
  			hue,
  			MathUtils.limit(saturation, 0f, 1f),
  			MathUtils.limit(brightness, 0f, 1f)
  		);
  	}
  
  	/**
  	 * Calculates the square of the distance between the two specified
  	 * Colors.
  	 * @param a Color.
  	 * @param b Color.
  	 * @return Square of distance.
  	 */
  	private static double distanceSq(Color a, Color b) {
  		double rMean = (a.getRed() + b.getRed()) / 256.0 / 2.0;
  		double dr = (a.getRed()   - b.getRed())   / 256.0;
  		double dg = (a.getGreen() - b.getGreen()) / 256.0;
  		double db = (a.getBlue()  - b.getBlue())  / 256.0;
  		double d = (2.0 + rMean)*dr*dr + 4.0*dg*dg + (2.0 + 1.0-rMean)*db*db;
  		return d / 9.0;
  	}
  
  	/**
  	 * Returns the current color variance.
  	 * @return Range of hue, saturation and brightness a color can have.
  	 */
  	public float[] getColorVariance() {
  		return colorVariance;
  	}
  
  	/**
  	 * Sets the current color variance.
  	 * @param colorVariance Range of hue, saturation and brightness a color
  	 *        can have.
  	 */
  	public void setColorVariance(float[] colorVariance) {
  		System.arraycopy(colorVariance, 0, this.colorVariance, 0, this.colorVariance.length);
  	}
  }
  