For a mouse with a click angle of 15 degrees things are unchanged. For devices
with angles less than 10, the current code scrolled way too fast. Because the
angle wasn't used anywhere, each tick would count as full scroll wheel event,
a slight movement of the wheel would thus scroll as much as a large movement
on a normal mouse.

Fix this by taking the actual click angle of the device into account. We
calculate some multiple of the angle that's close enough to the default 15
degrees of the wheel and then require that many click events to hit the full
scroll distance. For example, a mouse with a click angle of 3 degrees now
requires 5 clicks to trigger a full legacy scroll button event.

XI2.1 clients get the intermediate events (i.e. in this case five times
one-fifth of the scroll distance) and can thus scroll smoothly, or more
specifically in smaller events than usual.

https://bugs.freedesktop.org/show_bug.cgi?id=92772



Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>