code: function(p1, p2) {
  
        var s = this['SCALE'];
        var angle = (TAU + Math.atan2(p2[1] - p1[1], p2[0] - p1[0])) % TAU;
  
        return angle / TAU * s;
      }
docs: What is the angle of two points making a line
  
  @param {Array} p1
  @param {Array} p2
  @returns {number}