point-in-triangle/index.js

test whether a point is inside a triangle

//http://www.blackpawn.com/texts/pointinpoly/
module.exports = function pointInTriangle(point, triangle) {
    //compute vectors & dot products
    var cx = point[0], cy = point[1],
        t0 = triangle[0], t1 = triangle[1], t2 = triangle[2],
        v0x = t2[0]-t0[0], v0y = t2[1]-t0[1],
        v1x = t1[0]-t0[0], v1y = t1[1]-t0[1],
        v2x = cx-t0[0], v2y = cy-t0[1],
        dot00 = v0x*v0x + v0y*v0y,
        dot01 = v0x*v1x + v0y*v1y,
        dot02 = v0x*v2x + v0y*v2y,
        dot11 = v1x*v1x + v1y*v1y,
        dot12 = v1x*v2x + v1y*v2y

    // Compute barycentric coordinates
    var b = (dot00 * dot11 - dot01 * dot01),
        inv = b === 0 ? 0 : (1 / b),
        u = (dot11*dot02 - dot01*dot12) * inv,
        v = (dot00*dot12 - dot01*dot02) * inv
    return u>=0 && v>=0 && (u+v < 1)
}