Question

I’d like to write a program to remap user input for stuff like changing keyboard layouts, but also more complex things like making a shorthand program (i.e. “t qk fx jmps ovr t lzy dg” outputs as “the quick fox jumps over the lazy dog”). I’d prefer to do this at the X level or below.

Can I make some kind of virtual keyboard based on actual user output? Ideally I’d like some kind of simple interface (i.e. standard input to the program is a series of real user input events, output is the user input events for the virtual keyboard), but if that’s not possible I’d still be interested in pointers to how this can be done. I don’t know anything about Linux hardware devices, low-level X stuff, or the kernel right now; in fact I’m fairly new to Linux. Links to “Basics” tutorials would not be unappreciated.

Answer 1

You can use the Linux event subsystem to do this:

• Use the Linux input event interface (evdev) to receive events from any input device. See also the input.h header file for more information on the actual API.

• Use the EVIOCGRAB ioctl to grab the keyboard device, so that no other userspace applications but your daemon will receive any input events.

• Use the uinput interface to create a new virtual keyboard with any features that you need. See also the uinput.h header file for more information on the uinput API and this for a readable walkthrough.

There are a few applications that could serve as an example, such as EvRouter, ESE Key Daemon and my own evmapd.