There are couple of surprises around window interaction:

- Once a cursor starts to resize/move a window, those actions are not possible for the other one.
- One cursor can open a menu, and the other one can use it, that one works pretty well!
- Closing a window with one cursor, while the other drags it, makes the second one *disappear*! :D

I mean, these are really hard UI questions to solve! Often, it's not clear to me what the correct behavior should be!

Okay, let's try some applications, and see how they deal with multiple mice! 😈

First up: Gedit, a GTK application.

Both cursors can place the cursor and select text, but movement from one cursor "interrupts" the selection of the other one. Not very satisfying.

Imagine how cool it would be if both had their own selections + cursors!! That would allow a really neat form of collaboration within the same document!

Next up: Chromium! It has a very pragmatic solution: It just *ignores* all cursors but the first one!

In the video, the arrow-shaped cursor can click on stuff. The turtle has no power here.

In Firefox, it seems like all mouse events are mashed together, and are seen as coming from the same device.

That means that both cursors can click – if the other one "holds still". Otherwise, I guess Firefox is very confused by a click on a link while the mouse is not in it! 😆

Selections feel strange – the last-moving cursor will determine the selection.

Also notice how, if one cursor hovers a link, *both* turn into hand icons!

Of course, we *had* to try a drawing application next!

Here's @tldraw (in Firefox)! 

Collaborative drawing at it's best! 💚

Finally, I tried attaching an additional keyboard and assigned them to a different "seat"!

That worked really well! In Weston, each "seat" has its own keyboard focus, so you can actually work side-by-side with two mice + two keyboards independently!

Also!!! The two seats have their own (independent) clipboards!!!! Whatttt! 🤯

I totally didn't expect this. But multi-seat as a concept seems deeply integrated into libinput + #Wayland! Now it's up to GUI toolkits and compositors to support it!

Tried it again, and the independent clipboards still seem a bit glitchy after all… :(

An issue asking for proper support in GTK was closed five years ago, for example… https://gitlab.gnome.org/GNOME/gtk/-/issues/1574

Very useful when your very long line of code doesn't fit on your screen, for example! :P

(Shout-out to @xssfox, who first did this on X.org! https://sprocketfox.io/xssfox/2021/12/02/xrandr/)

Okay, here's how to set this up!

You need to create a udev rule for the "second" input device that sets ENV{WL_SEAT} to a string other than "default", and then start Weston from a virtual console. (At least, starting it from another Wayland session didn't work for me.) That's it!

The WL_SEAT property is what Wayland refers to as a "logical seat". Assign the same seat name to a mouse and a keyboard to make them work together! The default seat is "default".

Detailed steps:

1. Use `sudo libinput list-devices` to find the device file (like "/dev/input/event12")
2. Use `udevadm info -a /dev/input/event12` to find the parent device with a catchy ATTRS{name}.
3. Create a file /run/udev/rules.d/00-multiseat.rules like this:

ATTRS{name}="Name of your mouse" ENV{WL_SEAT}="second"

4. Run `sudo udevadm trigger` to apply the new rules.

You can check again with `sudo libinput list-devices`. The device's "Seat" should now say "seat0, second"!

You could try this script (requires zenity & possibly more tools? Please read before running!) https://github.com/n3rdopolis/rebeccablackos/blob/master/rebeccablackos_files/usr/bin/configureseats

(Doesn't work on #NixOS, where /etc/udev is read-only. 💀)

I'd love to have a little command line helper tool to help set this up, for an arbitrary number of mice! :D

This was a fun afternoon! Thanks for following along.

Let me know which other programs I should try with multiple mice! :D