Libgdx Wavy line

Hey, I’m trying to create a line that moves in a wave. Similar to the “milk” in Cookie Clicker (see: http://orteil.dashnet.org/cookieclicker/). I also want a color to be filled underneath the wave, I can only think of drawing a box under the line (obviously that wouldn’t look right);

I’d like to do it with ShapeRender, but I cannot think of the math needed or how to make a line bend.

Hopefully you understand what I’m trying to say.
Thanks.