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A modified version of some JGraph files
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/*
 * @(#)Spline2D.java
 * 
 * Copyright (c) 2003 Martin Krueger
 * Copyright (c) 2005 David Benson
 *  
 */
package org.jgraph.util;

import java.awt.geom.Point2D;

/**
 * Interpolates points given in the 2D plane. The resulting spline
 * is a function s: R -> R^2 with parameter t in [0,1].
 * 
 * @author krueger
 */
public class Spline2D {

	/** 
	 *	Array representing the relative proportion of the total distance
	 *	of each point in the line ( i.e. first point is 0.0, end point is
	 *	1.0, a point halfway on line is 0.5 ).
	 */
	private double[] t;
	private Spline splineX;
	private Spline splineY;
	/**
	 * Total length tracing the points on the spline
	 */
	private double length;
	
	/**
	 * Creates a new Spline2D.
	 * @param points
	 */
	public Spline2D(Point2D[] points) {
		double[] x = new double[points.length];
		double[] y = new double[points.length];
		
		for(int i = 0; i< points.length; i++) {
			x[i] = points[i].getX();
			y[i] = points[i].getY(); 
		}
		
		init(x, y);
	}

	/**
	 * Creates a new Spline2D.
	 * @param x
	 * @param y
	 */
	public Spline2D(double[] x, double[] y) {
		init(x, y);
	}

	private void init(double[] x, double[] y) {
		if (x.length != y.length) {
			throw new IllegalArgumentException("Arrays must have the same length.");
		}
		
		if (x.length < 2) {
			throw new IllegalArgumentException("Spline edges must have at least two points.");
		}

		t = new double[x.length];
		t[0] = 0.0; // start point is always 0.0
		
		// Calculate the partial proportions of each section between each set
		// of points and the total length of sum of all sections
		for (int i = 1; i < t.length; i++) {
			double lx = x[i] - x[i-1];
			double ly = y[i] - y[i-1];
			// If either diff is zero there is no point performing the square root
			if ( 0.0 == lx ) {
				t[i] = Math.abs(ly);
			} else if ( 0.0 == ly ) {
				t[i] = Math.abs(lx);
			} else {
				t[i] = Math.sqrt(lx*lx+ly*ly);
			}
			
			length += t[i];
			t[i] += t[i-1];
		}
		
		for(int i = 1; i< (t.length)-1; i++) {
			t[i] = t[i] / length;
		}
		
		t[(t.length)-1] = 1.0; // end point is always 1.0
		
		splineX = new Spline(t, x);
		splineY = new Spline(t, y);
	}

	/**
	 * @param t 0 <= t <= 1
	 */
	public double[] getPoint(double t) {
		double[] result = new double[2];
		result[0] = splineX.getValue(t);
		result[1] = splineY.getValue(t);

		return result;
	}
	
	/**
	 * Used to check the correctness of this spline
	 */
	public boolean checkValues() {
		return (splineX.checkValues() && splineY.checkValues());
	}

	public double getDx(double t) {
		return splineX.getDx(t);
	}
	
	public double getDy(double t) {
		return splineY.getDx(t);
	}
	
	public Spline getSplineX() {
		return splineX;
	}
	
	public Spline getSplineY() {
		return splineY;
	}
	
	public double getLength() {
		return length;
	}

}