Both dashed and zigzag use Math.atan:

      const alpha = Math.atan((p2[1] - p1[1]) / (p2[0] - p1[0]));

It would seem that a generated vertical line would cause errors. Is there a reason for preferring this over the safer atan2 alternative?

      const alpha = Math.atan2((p2[1] - p1[1]), (p2[0] - p1[0]));