src/main/java/eu/svjatoslav/sixth/e3d/geometry/Polygon.java

   1 /*
   2  * Sixth 3D engine. Copyright ©2012-2019, Svjatoslav Agejenko, svjatoslav@svjatoslav.eu
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of version 3 of the GNU Lesser General Public License
   6  * or later as published by the Free Software Foundation.
   7  *
   8  */
   9
  10 package eu.svjatoslav.sixth.e3d.geometry;
  11
  12 public class Polygon {
  13
  14     private static boolean intersectsLine(final Point2D point, Point2D p1,
  15                                           Point2D p2) {
  16
  17         if (p1.y > p2.y) {
  18             final Point2D tmp = p1;
  19             p1 = p2;
  20             p2 = tmp;
  21         }
  22
  23         if (point.y < p1.y)
  24             return false;
  25         if (point.y > p2.y)
  26             return false;
  27
  28         final double xp = p2.x - p1.x;
  29         final double yp = p2.y - p1.y;
  30
  31         final double yp2 = point.y - p1.y;
  32
  33         final double crossX = p1.x + ((xp * yp2) / yp);
  34
  35         return point.x >= crossX;
  36
  37     }
  38
  39     public static boolean pointWithinPolygon(final Point2D point,
  40                                              final Point2D p1, final Point2D p2, final Point2D p3) {
  41
  42         int intersectionCount = 0;
  43
  44         if (intersectsLine(point, p1, p2))
  45             intersectionCount++;
  46
  47         if (intersectsLine(point, p2, p3))
  48             intersectionCount++;
  49
  50         if (intersectsLine(point, p3, p1))
  51             intersectionCount++;
  52
  53         return intersectionCount == 1;
  54
  55     }
  56
  57 }