XI2 and MPX released!

It finally happened! After nearly 4 years of development, MPX has been released as part of XI2 in the new X Server 1.7.

The whole thing started when I started my PhD in late 2004. The problem I found was that there was no support for collaboration on a single shared display. All the solutions at the time were hacks at the toolkit or application level. I found that the only way we can get truly collaborative interfaces is by adding it into the windowing system itself. So started hacking on X in late 2005. I went from scratching my head and wondering how some of the stuff could compile (I had never heard of K&R function declarations) to rewriting large parts of the input subsystem and even ended up as release manager. Not in a single day though.

Now we're done. MPX is out, and we have generic low-level support for multiple input devices. You know the whole one keyboard-one mouse paradigm we've had since Doug Engelbart invented the mouse? It's over, you don't have to restrict yourself anymore when writing an app.

Of course, this is a low-level change and when you wake up tomorrow, not a lot will have actually changed. We still need the toolkits to support it, we need apps to pick it up, we need the desktop environments to start thinking about what can be made useful. Nonetheless, basic collaboration features are already there and it can only get better from here.

Let's see what will happen.

compiz with mpx support

Part two of my June work for the Uni/CSIRO was to modify compiz to support multiple input devices.

Get it now from git://people.freedesktop.org/~whot/compiz.git, checkout the mpx branch.

The current state: compiz core supports XI2, and the move, resize and annotate plugin support multiple devices. So you can wobble two windows at once if you feel like it - just for extra bling. Likewise, you can resize a window into 4 directions at once (I think so, only tested it with two).

The approach I took was fairly simple: in core, replace some functions (e.g. pushScreenGrab) with a device-specific one (pushDeviceGrab). This was done throughout the whole of compiz, and instead of core events, compiz now listens for XI events. In the plugins, replace the single variables with arrays/lists large enough for each device.

For the move/resize plugins I had to use an additional hack - the window decorator tells compiz over ICCCM that a resize/move operation has started. The ICCCM message doesn't include device ids and doesn't have any free bytes to stuff them in. The solution I found was to simply query all devices and find the one closest to the reported position - with the button 1 down.

In theory, the mpx-aware compiz should also work on a non-XI2 server but I haven't tested it.
The work is not finished with many details missing, but the core is there. I won't be able to continue on it as it was a project written under quite some time pressure and that time is up now.

I encourage you to take it and finish it off, it would be good to see a real window manager supporting XI2. If you have any questions about how to continue, pop me an email.