PC World Komputer 1997 May/Pcwk0597.iso/sybase/starbuck/java.z/Polygon.java

Text File | 1996-05-03 | 5KB | 186 lines

/*
 * @(#)Polygon.java    1.8 95/12/14 Sami Shaio
 *
 * Copyright (c) 1995 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and without
 * fee is hereby granted provided that this copyright notice
 * appears in all copies. Please refer to the file "copyright.html"
 * for further important copyright and licensing information.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 */
package java.awt;

/**
 * A polygon consists of a list of x and y coordinates.
 *
 * @version     1.8, 14 Dec 1995
 * @author     Sami Shaio
 * @author      Herb Jellinek
 */
public class Polygon {
    /**
     * The total number of points.
     */
    public int npoints = 0;

    /**
     * The array of x coordinates.
     */
    public int xpoints[] = new int[4];

    /**
     * The array of y coordinates.
     */
    public int ypoints[] = new int[4];

    /*
     * Bounds of the polygon.
     */
    Rectangle bounds = null;

    /**
     * Creates an empty polygon.
     */
    public Polygon() {
    }

    /**
     * Constructs and initializes a Polygon from the specified parameters.
     * @param xpoints the array of x coordinates
     * @param ypoints the array of y coordinates
     * @param npoints the total number of points in the Polygon
     */
    public Polygon(int xpoints[], int ypoints[], int npoints) {
    this.npoints = npoints;
    this.xpoints = new int[npoints];
    this.ypoints = new int[npoints];
    System.arraycopy(xpoints, 0, this.xpoints, 0, npoints);
    System.arraycopy(ypoints, 0, this.ypoints, 0, npoints);
    }

    /*
     * Calculate the bounding box of the points passed to the constructor.
     * Sets 'bounds' to the result.
     */
    void calculateBounds(int xpoints[], int ypoints[], int npoints) {
    int boundsMinX = Integer.MAX_VALUE;
    int boundsMinY = Integer.MAX_VALUE;
    int boundsMaxX = Integer.MIN_VALUE;
    int boundsMaxY = Integer.MIN_VALUE;

    for (int i = 0; i < npoints; i++) {
        int x = xpoints[i];
        boundsMinX = Math.min(boundsMinX, x);
        boundsMaxX = Math.max(boundsMaxX, x);
        int y = ypoints[i];
        boundsMinY = Math.min(boundsMinY, y);
        boundsMaxY = Math.max(boundsMaxY, y);
    }
    bounds = new Rectangle(boundsMinX, boundsMinY,
                   boundsMaxX - boundsMinX,
                   boundsMaxY - boundsMinY);
    }

    /*
     * Update the bounding box to fit the point x, y.
     */
    void updateBounds(int x, int y) {
    bounds.x = Math.min(bounds.x, x);
    bounds.width = Math.max(bounds.width, x - bounds.x);
    bounds.y = Math.min(bounds.y, y);
    bounds.height = Math.max(bounds.height, y - bounds.y);
    }

    /**
     * Appends a point to a polygon.  If inside(x, y) or another
     * operation that calculates the bounding box has already been
     * performed, this method updates the bounds accordingly.

     * @param x the x coordinate of the point
     * @param y the y coordinate of the point
     */
    public void addPoint(int x, int y) {
    if (npoints == xpoints.length) {
        int tmp[];

        tmp = new int[npoints * 2];
        System.arraycopy(xpoints, 0, tmp, 0, npoints);
        xpoints = tmp;

        tmp = new int[npoints * 2];
        System.arraycopy(ypoints, 0, tmp, 0, npoints);
        ypoints = tmp;
    }
    xpoints[npoints] = x;
    ypoints[npoints] = y;
    npoints++;
    if (bounds != null) {
        updateBounds(x, y);
    }
    }

    /**
     * Determines the area spanned by this Polygon.
     * @return a Rectangle defining the bounds of the Polygon.
     */
    public Rectangle getBoundingBox() {
    if (bounds == null) {
        calculateBounds(xpoints, ypoints, npoints);
    }
    return bounds;
    }

    /**
     * Determines whether the point (x,y) is inside the Polygon. Uses
     * an even-odd insideness rule (also known as an alternating
     * rule).

     * @param x the X coordinate of the point to be tested
     * @param y the Y coordinate of the point to be tested
     *
     * <p>Based on code by Hanpeter van Vliet <[e-mail]>.
     */
    public boolean inside(int x, int y) {
    if (getBoundingBox().inside(x, y)) {
        int hits = 0;

        // Walk the edges of the polygon
        for (int i = 0; i < npoints; i++) {
        int j = (i + 1) % npoints;

        int dx = xpoints[j] - xpoints[i];
        int dy = ypoints[j] - ypoints[i];

        // ignore horizontal edges completely
        if (dy != 0) {
            // Check to see if the edge intersects
            // the horizontal halfline through (x, y)
            int rx = x - xpoints[i];
            int ry = y - ypoints[i];

            // Quick and dirty way to deal with vertices
            // that fall exactly on the halfline
            if (ypoints[i] == y) ry--;
            if (ypoints[j] == y) dy++;

            float s = (float)ry / (float)dy;
            if (s >= 0.0 && s <= 1.0) {
            if ((int)(s * dx) > rx) hits++;
            }
        }
        }

        return (hits % 2) != 0;
    }
    return false;
    }
}