X11: Mouse motion events sometimes contain garbage

[valaphee]

While printing out events on X11, I noticed that sometimes (not always), the motion events are invalid:

DeviceEvent { device_id: DeviceId(X(DeviceId(2))), event: Motion { axis: 0, value: -1.0 } }
DeviceEvent { device_id: DeviceId(X(DeviceId(2))), event: Motion { axis: 1, value: 7.1e-322 } }
DeviceEvent { device_id: DeviceId(X(DeviceId(2))), event: MouseMotion { delta: (-1.0, 7.1e-322) } }

Only one axis gets reported and the second axis is just an unrelated value (most likely smth not belonging to the event).

for i in 0..xev.valuators.mask_len * 8 {
    if !xinput2::XIMaskIsSet(mask, i) {
        continue;
    }
    let x = unsafe { *value };

The easiest way I found to reproduce this is just moving the cursor between two monitors. It might also just be a x11 problem.

I'm running natively latest Arch Linux with Gnome using X11.

[notgull]

7.1e-322 is really close to zero, which makes me think this is an error in interpreting the data from the X11 server.

Can you reproduce this issue while running xtrace, then attach the logs?

[valaphee]

XIRawEvent raw_values are used instead of XIRawEvent valuators values:

winit/src/platform_impl/linux/x11/event_processor.rs

Line 1418 in e61a732

let mut value = xev.raw_values;

Replacing raw values with values yields way higher precision, (raw values only indicate if a value is zero, positive or negative at least with mouse devices) and doesn't has this problem.

I'll try to get a trace.