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FreeHEP GraphicsIO Base Library
There is a newer version: 2.4
// Copyright 2001 FreeHEP.
package org.freehep.graphicsio;

import java.awt.geom.Point2D;
import java.io.IOException;
import java.util.Stack;

/**
 * Implements cubics by approximating them using a polyline. Useful class for
 * output formats that do NOT implement bezier curves at all, or if you need
 * only straight lines.
 * 
 * @author Mark Donszelmann
 * @version $Id: freehep-graphicsio/src/main/java/org/freehep/graphicsio/CubicToLinePathConstructor.java db80b97becbb 2006/03/09 01:16:21 duns $
 */
public abstract class CubicToLinePathConstructor extends
        QuadToCubicPathConstructor {

    private double resolution;

    protected CubicToLinePathConstructor() {
        this(0.025);
    }

    protected CubicToLinePathConstructor(double resolution) {
        this.resolution = Math.abs(resolution);
    }

    public void cubic(double x1, double y1, double x2, double y2, double x3,
                      double y3) throws IOException {

        // ControlSets are written at the end
        Stack/**/ controls = new Stack/**/();

        // System.out.println("Cubic "+x1+" "+y1+" "+x2+" "+y2+" "+x3+" "+y3);
        Point2D p0 = new Point2D.Double(currentX, currentY);
        Point2D p1 = new Point2D.Double(x1, y1);
        Point2D p2 = new Point2D.Double(x2, y2);
        Point2D p3 = new Point2D.Double(x3, y3);

        // ControlSets to create the controls
        Stack/**/ temps = new Stack/**/();
        temps.push(new ControlSet(p0, p1, p2, p3));

        while (!temps.empty()) {
            ControlSet control = temps.pop();
            if (control.breadth() > resolution) {
                temps.push(control);
                temps.push(control.bisect());
            } else {
                controls.push(control);
            }
        }

        /*tempSet[l++] = new ControlSet(p0, p1, p2, p3);
        while (l > 0) {
            ControlSet control1 = tempSet[--l];
            double b = control1.breadth();
            if (b > resolution) {
                ControlSet control3 = control1.bisect();
                tempSet[l++] = control1;
                tempSet[l++] = control3;
            } else {
                controls.push(control1);
            }
        }*/

        // write out control sets
        // System.out.println(k);
        while (!controls.empty()) {
            Point2D p = controls.pop().getPoint();
            line(p.getX(), p.getY());
            // System.out.println(control2.getPoint());
        }

        // store currentX and currentY
        super.cubic(x1, y1, x2, y2, x3, y3);
    }

    class ControlSet {
        private Point2D point0;

        private Point2D point1;

        private Point2D point2;

        private Point2D point3;

        public ControlSet(Point2D p0, Point2D p1, Point2D p2, Point2D p3) {
            point0 = p0;
            point1 = p1;
            point2 = p2;
            point3 = p3;
        }

        public double breadth() {
            double f0 = point0.getX();
            double f4 = point0.getY();
            double f1 = point1.getX();
            double f5 = point1.getY();
            double f2 = point2.getX();
            double f6 = point2.getY();
            double f3 = point3.getX();
            double f7 = point3.getY();
            if ((Math.abs(f0 - f3) < resolution)
                    && (Math.abs(f4 - f7) < resolution)) {

                double f8 = Math.abs(f1 - f0) + Math.abs(f5 - f4);
                double f10 = Math.abs(f2 - f0) + Math.abs(f6 - f4);
                return Math.max(f10, f8);

            } else {

                double d0 = f4 - f7;
                double d1 = f3 - f0;
                double f12 = Math.sqrt(d0 * d0 + d1 * d1);
                double d2 = f3 * f4 - f0 * f7;
                double f9 = Math.abs((d0 * f2 + d1 * f6) - d2) / f12;
                double f11 = Math.abs((d0 * f1 + d1 * f5) - d2) / f12;
                return Math.max(f9, f11);
            }
        }

        public ControlSet bisect() {
            Point2D p0 = average(point0, point1);
            Point2D p1 = average(point1, point2);
            Point2D p2 = average(point2, point3);
            Point2D p3 = average(p0, p1);
            Point2D p4 = average(p1, p2);
            Point2D p5 = average(p3, p4);
            ControlSet controlset = new ControlSet(p5, p4, p2, point3);
            point1 = p0;
            point2 = p3;
            point3 = p5;
            return controlset;
        }

        public Point2D average(Point2D p1, Point2D p2) {
            return new Point2D.Double((p1.getX() + p2.getX()) / 2.0,
                    (p1.getY() + p2.getY()) / 2.0);
        }

        public Point2D getPoint() {
            return point3;
        }
    }

}