Peter Hutterer authored Nov 22, 2018 and José Expósito committed Aug 31, 2021

Starting with kernel v5.0 two new axes are available for high-resolution wheel
scrolling: REL_WHEEL_HI_RES and REL_HWHEEL_HI_RES. Both axes send data in
fractions of 120 where each multiple of 120 amounts to one logical scroll
event. Fractions of 120 indicate a wheel movement less than one detent.

This commit adds a new API for scroll events. Three new event types that encode
the axis source in the event type name and a new API to get a normalized-to-120
value that also used by Windows and the kernel (each multiple of 120 represents
a logical scroll click).

This addresses a main shortcoming with the existing API - it was unreliable to
calculate the click angle based on the axis value+discrete events and thus any
caller using the axis value alone would be left with some ambiguity. With the
v120 API it's now possible to (usually) calculate the click angle, but more
importantly it provides the simplest hw-independent way of scrolling by a
click or a fraction of a click....