Useful function to detect one of side direction by two vectors. This for elements with 8 different sprites for each side. Based on scalar product.

getDirection.js

function getSide(from, to) {
  
  /*
   * For nord returns 0, for east - 2, and so on
   * Lot of things simplified
   * As max and min scalar product is always opposite, than we need to check only some of scalar product
   * For example scalar product for nord:
   * var nord = {x: 0, y: 1}
   * var d0 = x * nord.x + y * nord.y
   * x * 0 + y * 1 = y
   * So scalar product for nord d0 = y, in this case d0 is simplified
   */

    // Direction vector
    var x = to.x - from.x;
    var y = to.y - from.y;

    var d1, d3, d7;

    d1 = (x + y) * 0.71;

    if (d1 > y) {

        if (x <= d1) {
            return 1;
        }

        d3 = (x - y) * 0.71;

        if (d3 <= x) {
            return 2;
        }

        if (-y <= d3) {
            return 3;
        }

        if (-d1 <= -y) {
            return 4;
        }

    } else {

        if (d1 === y) {
            return 0;
        }

        d7 = (y - x) * 0.71;

        if (d7 <= y) {
            return 0;
        }

        if (-x <= d7) {
            return 7;
        }

        if (-d1 <= -x) {
            return 6;
        }

        if (-y <= -d1) {
            return 5
        }

        d3 = (x - y) * 0.71;

        if (d3 <= -y) {
            return 4;
        }
    }
}