Multi-touch gestures in Mutter-based compositors

A customer has asked for documentation on handling multi-touch gestures in their Mutter-based compositor (see my previous post) and I thought that it could be a good idea to have it in the GNOME wiki, in case it helps when they are added to GNOME Shell:

Multi-touch gestures in Mutter-based compositors

I'm not sure of what would be the best use for multi-touch gestures in the Shell, probably for resizing windows (with a 4-finger pinch gesture) or for switching desktops (with a 3 or 4 finger swipe). Probably some ideas can be taken from the multi-tasking gestures in recent versions of iOS, such as using pinch gestures to activate hidden panels or to switch to another views.

Something I feel strongly is about restricting system-wide gestures to more than 3 fingers, because the user experience and the implementation gets quite complicated if the compositor and the applications need to compete for touch sequences in similar gestures.

It's currently a bit convoluted due to zero support in Mutter for touch events, but once the Shell starts using touch events, I think it will make sense to move some of the setup and boilerplate into Mutter.

Once more, thanks to my employer Collabora for sponsoring this work:

Multi-touch gestures in Gnome Shell

I'm keeping this small branch in which touch event support is added to Mutter. Plug-ins can register to get touch events before any other client and then accept or reject touch sequences depending on whether the shell is interested on the gesture or not.

As can be seen in this example of a mutter plug-in, any subclass of ClutterGestureAction can be used, which includes gesture recognizers for pan, zoom and rotate actions, but creating new recognizers is pretty easy.

The mutter branch is up for reviewing in bugzilla and any comments on the approach will be very welcome. And if anybody wants to play with multi-touch gestures in Gnome Shell, please link to your work from the wiki so we can track it.

If anybody from the design team has already started thinking about this, I would be very glad to hear their thoughts on this.

As always, I'm grateful to my employer Collabora for sponsoring this work, and I hope GNOME benefits from it.

Touch events within Xephyr

As part of my ongoing work on multi-touch, I have been looking at handling touch gestures within Mutter plugins. Developing a X window manager/shell can be quite a hassle because you are likely to want to do that in a separate X display so your testing doesn't disturb the session where you do the actual coding.

In the past I have used Xephyr to run a nested X display so I can run the window manager as I would run any normal application, but this time I found that Xephyr doesn't forward any XInput2 events right now, which is needed for MT. Having a separate machine where to test is an alternative but it has been quite uncomfortable.

My colleague at Collabora Daniel Stone encouraged me to give it a try and it indeed didn't take much work to get something running, though I still haven't tested it much.

So for the code, here is the Xephyr repo: http://cgit.collabora.com/git/user/tomeu/xserver/log/?h=xephyr-touch

And here the Mutter repo: http://cgit.collabora.com/git/user/tomeu/mutter/log/?h=touch-clutter

Remember that these are early proof-of-concepts, but if you give it a try and want to give feedback, it will be welcome.

As usual, thanks to my employee Collabora for sponsoring this work and letting me share it.