xfwm: xinput2 change causes weird scroll event buffering

[André Miranda]

Hi Jan,
I suggest you open an issue at gitlab.xfce.org/xfce/xfwm4 if you haven't
done yet.

Cheers,
Andre Miranda

On Tue, Aug 18, 2020 at 10:36 AM Jan Engelhardt <jengelh at inai.de> wrote:

> Greetings.
>
>
> I have here a Fujitsu U728 laptop, which has the following xinput
> pointy devices:
>
> ⎡ Virtual core pointer                          id=2    [master pointer
> (3)]
> ⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer
> (2)]
> ⎜   ↳ ELAN0D01:00 04F3:3092 Touchpad            id=16   [slave  pointer
> (2)]
> ⎜   ↳ Dell Dell Wired Multimedia Keyboard Mouse id=11   [slave  pointer
> (2)]
> ⎜   ↳ USB Optical Mouse                         id=13   [slave  pointer
> (2)]
> ⎜   ↳ ETPS/2 Elantech Touchpad                  id=18   [slave  pointer
> (2)]
> ⎜   ↳ ELAN0D01:00 04F3:3092 Mouse               id=15   [slave  pointer
> (2)]
>
> Mouse handling has regressed for me since xfwm4 switched to xinput2 in
> commit 6013f1ee9b3831991db6a0fb896f20537532b6ce.
> After changing from 68b6854 to 6013f1, I notice a problem:
>
>  - When a number of scroll events have been issued through either
>    touchpad or USB mouse,
>  - applications such as firefox, inkscape, leafpad,
>  - but _not_ xterm, xev, xfce4-terminal(-0.8.9.2), or gtk3-demo,
>
> something in xfwm "dies" and
>
>  - mouse events (click, scroll) get weirdly "buffered",
>  - mouse movement on screen is possible,
>  - but application receives no practical events, i.e. mouse cursor
>    does not change when changing between plaintext and hyperlinks in
>    firefox / buttons below mouse cursor no longer change color from/to
>    their button highlight.
>
> Then, when an interrupt happens, such as,
>
>  - a keyboard key is pressed
>  - any USB or DP/HDMI cable is (dis)connected
>  - analog audio cable is (dis)connected (there's support for Presence
> Detect),
>
> the most recent 5-or-so events so buffered get delivered.
>
> What I notice is that the U728 touchpad is represented as three
> different xinput devices (15,16,18). For comparison, on a Lenovo X240
> with a similar modern version of xfwm (that uses xinput2), there is
> no issue observable, but the Lenovo touchpad is only present as one
> xinput device. Not sure if that has anything to do with it...
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