There must be an API because I've seen (felt?) it used recently. I can't remember what app it was, one I just have tried one time. It had a knob like control an

There must be an API because I've seen (felt?) it used recently. I can't remember what app it was, one I just have tried one time. It had a knob like control and as you dragged around it made the trackpad click like a real knob might as you turn it. I didn't find this very compelling, would rather a slider.