Java Geometry Polygon inside_polygon(float[] xpts, float[] ypts, double ptx, double pty)

Description

Tests if a point is inside a polygon.

License

Open Source License

Parameter

Parameter	Description
xpts	horizontal pixel window points of polygon.
ypts	vertical pixel window points of polygon.
ptx	horizontal pixel window points of location
pty	vertical pixel window points of location.

Return

boolean

Declaration

public final static boolean inside_polygon(float[] xpts, float[] ypts, double ptx, double pty) 

Method Source Code

//package com.java2s;

import java.awt.geom.Point2D;

public class Main {
    /**/*from w ww  . j  av a 2 s  .  c  om*/
     * Tests if a point is inside a polygon.
     * <p>
     * 
     * @param xpts horizontal pixel window points of polygon.
     * @param ypts vertical pixel window points of polygon.
     * @param ptx horizontal pixel window points of location
     * @param pty vertical pixel window points of location.
     * @return boolean
     */
    public final static boolean inside_polygon(float[] xpts, float[] ypts, double ptx, double pty) {

        int j, inside_flag = 0;
        int numverts = xpts.length;
        if (numverts <= 2)
            return false;
        Point2D vtx0 = new Point2D.Float(), vtx1 = new Point2D.Float();
        double dv0; // prevents OVERFLOW!!
        int crossings = 0;
        boolean xflag0 = false, yflag0 = false, yflag1 = false;

        vtx0.setLocation(xpts[numverts - 1], ypts[numverts - 1]);
        // get test bit for above/below Y axis
        yflag0 = ((dv0 = vtx0.getY() - pty) >= 0);

        for (j = 0; j < numverts; j++) {
            if ((j & 0x1) != 0) { // HACK - slightly changed
                vtx0.setLocation(xpts[j], ypts[j]);
                yflag0 = ((dv0 = vtx0.getY() - pty) >= 0);
            } else {
                vtx1.setLocation(xpts[j], ypts[j]);
                yflag1 = (vtx1.getY() >= pty);
            }

            /*
             * check if points not both above/below X axis - can't hit ray
             */
            if (yflag0 != yflag1) {
                /* check if points on same side of Y axis */
                if ((xflag0 = (vtx0.getX() >= ptx)) == (vtx1.getX() >= ptx)) {
                    if (xflag0)
                        crossings++;
                } else {
                    crossings += ((vtx0.getX()
                            - dv0 * (vtx1.getX() - vtx0.getX()) / (vtx1.getY() - vtx0.getY())) >= ptx) ? 1 : 0;
                }
            }
            inside_flag = crossings & 0x01;
        }
        return (inside_flag != 0);
    }
}

Related

1. boundingTest(Polygon p, int x, int y, int w, int h)
2. makeArea(Polygon polygon, int steps, int dX, int dY)
3. polyArea(Polygon target)
4. regularPolygon(int sides, double x, double y, double width, double height)
5. sparsifyPolygon(java.awt.Polygon p, double minDistance)