code: function (x1, y1, x2, y2) {
              return Math.atan2(y2 - y1, x2 - x1) * 180 / Math.PI;
          }
docs: Returns the angle of the line defined by two points, and the x axes.
  @param {Integer} x1 x of the first point
  @param {Integer} y1 y of the first point
  @param {Integer} x2 x of the second point
  @param {Integer} y2 y of the second point
  @private
  @return {Number} the angle in degrees ]-180; 180]