Polygon.java

/*
 *  Copyright (C) 2014  Alfons Wirtz  
 *   website www.freerouting.net
 *
 *   This program is free software: you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, either version 3 of the License, or
 *   (at your option) any later version.
 *
 *   This program 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 General Public License at <http://www.gnu.org/licenses/> 
 *   for more details.
 */

package geometry.planar;

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;

/**
 *
 * A Polygon is a list of points in the plane, where no 2 consecutive
 * points may be equal and no 3 consecutive points collinear.
 *
 * @author Alfons Wirtz#
 */


public class Polygon implements java.io.Serializable
{
    /**
     * Creates a polygon from p_point_arr.
     * Multiple points and points, which are collinear with its previous
     * and next point will be removed.
     */
    public Polygon(Point [] p_point_arr)
    {
        corners = new LinkedList<Point>();
        if (p_point_arr.length == 0)
        {
            return;
        }
        for (int i = 0; i < p_point_arr.length; ++i)
        {
            corners.add(p_point_arr[i]);
        }

        boolean corner_removed = true;
        while (corner_removed)
        {
            corner_removed = false;
            // remove multiple points

            if (corners.isEmpty())
            {
	        return;
            }
            Iterator<Point> i = corners.iterator();
            Point curr_ob = i.next();
            while(i.hasNext())
            {
	        Point next_ob = i.next();
	        if(next_ob.equals(curr_ob))
	        {
	            i.remove();
	            corner_removed = true;
	        }
	        else
	        {
	            curr_ob = next_ob;
	        }
            }

            // remove points which are collinear with  the previous
            // and next point.
            i = corners.iterator();
            Point prev = i.next();
            Iterator<Point> prev_i = corners.iterator();
            if (!i.hasNext())
            {
	        continue;
            }
            Point curr  = i.next();
            prev_i.next();
            while(i.hasNext())
            {
                Point next = i.next();
	        prev_i.next();

	        if(curr.side_of(prev, next) == Side.COLLINEAR)
	        {
	            prev_i.remove();
	            corner_removed = true;
	            break;
            }
	        prev = curr;
	        curr = next;
            }
        }
    }

    /**
     * returns the array of corners of this polygon
     */
    public Point[] corner_array()
    {
        int corner_count = corners.size();
        Point[] result = new Point[corner_count];
        Iterator<Point> it = corners.iterator();
        for (int i = 0; i < corner_count;  ++i)
        {
            result[i] = it.next();
        }
        return result;
    }
    
    /** 
     * Reverts the order of the corners of this polygon.
     */
    public Polygon revert_corners()
    {
        Point [] corner_arr = corner_array();
        Point [] reverse_corner_arr = new Point[corner_arr.length];
        for (int i = 0; i < corner_arr.length; ++i)
        {
           reverse_corner_arr[i] =  corner_arr [corner_arr.length - i - 1];
        }
        return new Polygon(reverse_corner_arr);
    }
    /**
     * Returns the winding number of this polygon, treated as closed.
     * It will be > 0, if the corners are in countercock sense,
     * and < 0, if the corners are in clockwise sense.
     */
    public int winding_number_after_closing()
    {
        Point [] corner_arr = corner_array();
        if (corner_arr.length < 2)
        {
            return 0;
        }
        Vector first_side_vector = corner_arr[1].difference_by(corner_arr[0]);
        Vector prev_side_vector = first_side_vector;
        int corner_count = corner_arr.length;
        // Skip the last corner, if it is equal to the first corner.
        if (corner_arr[0].equals(corner_arr[corner_count - 1]))
        {
            --corner_count;
        }
        double angle_sum = 0;
        for (int i = 1; i <= corner_count; ++i)
        {
            Vector next_side_vector;
            if (i == corner_count - 1)
            {
                next_side_vector = corner_arr[0].difference_by(corner_arr[i]);
            }
            else if (i == corner_count)
            {
                next_side_vector = first_side_vector;
            }
            else
            {
                  next_side_vector = corner_arr[i + 1].difference_by(corner_arr[i]);
            }
            angle_sum +=  prev_side_vector.angle_approx(next_side_vector);
            prev_side_vector = next_side_vector;
        }
        angle_sum /= 2.0 * Math.PI;
        if (Math.abs(angle_sum) < 0.5)
        {
            System.out.println ("Polygon.winding_number_after_closing: winding number != 0 expected");
        }
        return (int) Math.round(angle_sum);
    }

    private final Collection<Point> corners;
}