Re: [PATCH] ui/gtk: Fix relative mouse with multiple monitors

[Dennis Wölfing]

On 19.07.21 13:31, Marc-André Lureau wrote:
> Hi Dennis
>
> On Tue, Jun 29, 2021 at 5:26 PM Dennis Wölfing <denniswoelfing@gmx.de> wrote:
>
> > To handle relative mouse input the event handler needs to move the mouse
> > away from the screen edges. Failing to do so results in the mouse
> > getting stuck at invisible walls. However the current implementation for
> > this is broken on hosts with multiple monitors.
> >
> > With multiple monitors the mouse can be located outside of the current
> > monitor which is not handled by the current code. Also the monitor
> > itself might be located at coordinates different from (0, 0).
> >
> > Signed-off-by: Dennis Wölfing <denniswoelfing@gmx.de>
>
>
> Looks reasonable to me. In spice-gtk we have slightly different code, we
> wrap at the middle of the monitor instead
> (https://gitlab.freedesktop.org/spice/spice-gtk/-/blob/master/src/spice-widget.c#L1214),
> what do you think?

Indeed, warping to the center of the monitor allows for simpler code and
means that it will take longer until the cursors hits a border again.
I'll send a v2 that warps to the middle of the monitor.

> And also, spice-gtk has special cases for w32 and wayland, which behave
> differently.

I just tested QEMU on a Windows host and relative mouse input is quite
broken both before and after this patch: As soon as the cursor leaves
the window QEMU no longer receives mouse events until the cursor is
moved back into the window. I haven't tested it with Wayland.
So we should perhaps have similar special cases as in spice-gtk. However
I'm not comfortable with writing a patch to fix this as I am not
familiar with the Windows and Wayland APIs.

> Gtk4 is also different, as device_warp() is gone (it will have to handle
> it specifically again for the different platforms:
> https://gitlab.gnome.org/malureau/rdw/-/blob/master/rdw/src/display.rs#L812)

That is unfortunate. The code will need to be rewritten then when it
updated for Gtk4.