multiply uv.y by the amount of lines you want, then floor it for line indices, then use that as a seed for a random float which determines the lines length, which then goes into a step function against the uv.x
multiply uv.y by the amount of lines you want, then floor it for line indices, then use that as a seed for a random float which determines the lines length, which then goes into a step function against the uv.x