JavaScript implementation of winding number algorithm to determine whether a point is inside a polygon

point_in_polygon_using_winding_number.js

//JavaScript implementation of winding number algorithm to determine whether a point is inside a polygon
//Based on C++ implementation of wn_PnPoly() published on http://geomalgorithms.com/a03-_inclusion.html

function pointInPolygon(point, vs) {    
    var x = parseFloat(point[0]), y = parseFloat(point[1]);

    var wn = 0;

    for (var i = 0, j = vs.length - 1; i < vs.length; j = i++) {
      var xi = parseFloat(vs[i][0]), yi = parseFloat(vs[i][1]);
      var xj = parseFloat(vs[j][0]), yj = parseFloat(vs[j][1]);

      if (yj <= y) {
        if (yi > y) {
          if (isLeft([xj, yj], [xi, yi], [x,y]) > 0) {
            wn++;
          }
        }
      } else {
        if (yi <= y) {
          if (isLeft([xj, yj], [xi, yi], [x, y]) < 0) {
            wn--;
          }
        }
      }
    }

    return wn != 0;
};


function isLeft(P0, P1, P2)
{
    var res = ( (P1[0] - P0[0]) * (P2[1] - P0[1])
            - (P2[0] -  P0[0]) * (P1[1] - P0[1]) );
    return res;
}

You are awesome :)

Can you tell me how to use it please!?

You are awesome! I needed this magic :)

@SebaMederos

point is an array of size 2 containing the x and y co-ordinates of the point you want to test, i.e. point[0] is x and point[1] is y.

vs is an array containing the vertices of the polygon, each element is an array of size 2 containing the vertex's x and y co-ordinates.

Take this example in which we want to test if two points pointA and pointB are contained inside the square mySquare which is centred around 0,0 and has a side length of two.

mySquare = [[-1,1], [1,1], [1,-1], [-1,-1]];

pointA = [0.5,0.5];
pointB = [2,2];

pointInPolygon(pointA, mySquare) will return true;
pointInPolygon(pointB, mySquare) will return false;