Bends the picture into ripples, like a reflection in disturbed water or a badly tracking video tape.
It is one line of arithmetic. Each pixel looks at its horizontal position, feeds that to a sine wave, and shifts where it reads from vertically by the result. Move across the picture and the shift rises and falls, so straight lines come out wavy.
scale sets how many ripples fit across the frame and strength how far they bend. speed sends them travelling, in whole cycles so the motion loops seamlessly.
rotation is the useful one and it works in an indirect way: the coordinates are turned before the ripple is applied and turned back afterwards, so the wave runs at whatever angle you like while the picture itself stays upright. wrap decides what fills the strip at the top and bottom that the bending pushes out of frame.