I need to build a simple app that takes (click only) input from 4 USB mice connected in addition to the built-in touchpad on a notebook. My preferred operating system for this setup would be Linux.
Any idea how I might be able to discern in an application which mouse a click came from? I'm open to C programming or whatever it takes. It's a simple, one-off project, so nothing too elaborate though.
Check out these links. Also, here you may find a code sample on how to deal with multiple mouse pointers in MPX.
I'm not too sure where to start for this, but it sounds a lot to me like it'd be similar to getting multi-touch to work. Maybe start looking for multi-touch drivers for linux?
Also, luvieere's first link might be helpful.
MPX is where it's at for multiple-mouse and multitouch under Linux, but you'll need to be using xorg xserver 1.7 to get the ‘proper’ version of it; this is generally taken as part of X11R7.5, which has only just come out as ‘stable’ and has not been integrated by the distros yet. (Even xorg-edgers doesn't have it, though that's where you'd keep an eye on if you're an Ubuntu-er.)
GTK+ seems to have had some work put into allowing you to detect which mouse clicked (GdkEvent.gdk_event_get_device), but I don't know what the timetable is for getting this into a full stable release. Nor do I know how far along Qt4 is with it. So in summary the situation is: it works if you're willing to put the time into grabbing, compiling and fixing stuff, but it's not smooth with mainstream Linux, yet.
For what it's worth, I think I found an answer to my question.
bobince's mention of xorg led me to look in /etc/X11/xorg.conf. That turns out to be full of comments like
# commented out by update-manager, HAL is now used
I had heard of HAL before, and not just in 2001. I tried man -k hal and found lshal, which lists 133 (!) HAL devices in my PC. In the entry for one of my mice, I found
linux.sysfs_path = '/sys/devices/pci0000:00/0000:00:0b.0/usb2/2-7/2-7:1.0/input/input6/event6'
which turns out to be a directory in the file system. Exploring from there, I discovered a reference back to /dev/input/mouse3. In fact, all my mice were sitting there in /dev/input!
Wearing my superuser cape, I was able to read /dev/input/mouse3:
root@carl-ubuntu:/dev/input# od -t x1 -w6 mouse3
0000000 09 00 00 08 00 00
*
so it turns out a left mouse click is 09 00 00 08 00 00, consistently and repeatably.
Conclusion: I can read mouse clicks from /dev/input/mouseX. Having done chmod a+r on those files, I can even read them from a normal user account. I need to figure out a way to stop 4 mice running wild in the hands of probably drunk people from actually interacting directly with the GUI, but that's a problem for another day.