In libinput 1.19, three new pointer axis events were added in order to provide support for high-resolution scrolling.
LIBINPUT_EVENT_POINTER_AXIS is de-facto deprecated and new users of libinput should use instead SCROLL_WHEEL, SCROLL_FINGER, and SCROLL_CONTINUOUS.
Discrete deltas were replaced with v120 delta values. 120 corresponds to a single discrete delta. Smaller values correspond to "partial" wheel ticks.