ultra-scroll enables fast, smooth, jump-free scrolling for Emacs on
all builds that support varying pixel scroll delta event data.  On
emacs-mac it retains the swipe-to-scroll and pinch-out for tab
overview capabilities of that port.  On all ports, it can scroll
past images or other content taller than the window without issue.

The strongly recommended scroll settings are:

 scroll-margin=0

See also `pixel-scroll-precision-mode' in pixel-scroll.el.