Comment 2 for bug 1558498

There's a demo of it here: https://www.youtube.com/watch?v=fiEkCaA_P7c

See about 2:30.

Looking closely at the swipe it seems to be slightly arc shaped, but I don't know if that is strictly neccessary. I'll try and get confirmation on that.

From an api perspective, I think a starting x,y and ending x,y should be sufficent, which is based on the middle touch point. Optional rate and width parameters could be added to control speed and width of the spacing. From the video it looks like the width remains constant and all the 3 touch points move in unison.