The current algorithm triggers a bug in Xwayland when two devices have
different granularity of scrolling. In Xwayland, the scroll increment is
1 and all physical devices scroll through the same (x)wayland pointer
device.
This may cause events to get lost when changing devices:
- mouse scrolls by full increment, current value is 1.0
last scroll button was sent for valuator value 0.0,
delta is 1.0 and we emulate a button event.
- touchpad scrolls by partial increment, current value is 1.3
last scroll button was sent for valuator value 1.0, delta is 0.3
and no button event is emulated
- mouse scrolls by full increment, current value is -0.7,
last scroll button was sent for valuator value 1.0, delta is -0.7
and no button event is emulated
Thus the wheel event appears to get lost. Xwayland cannot reliably
detect this case because we don't see the physical devices.
We can work around this by instead emulating buttons whenever we cross
a multiple of increment. However, this has a drawback:
high-resolution scroll devices can now trigger a button event storm by
jittering across the multiple of increment. e.g. in the example above
the touchpad moving from 1.3 to 1.0 would cause a click, despite this
being a third of an increment.
Fixes#1339
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Olivier Fourdan <ofourdan@redhat.com>
0a22502c34