Today I realized Gnome has support for XF86XK_TouchpadToggle, i.e. if you press the key in your keyboard that has the touchpad with an X symbol over it, it toggles the enabled state of the touchpad.
This is very useful if you are like me and attach/detach a mouse various times during the day.
Since as far as I know this is not supported in KDE, this afternoon I decided to write a quick kded module that would listen to XF86XK_TouchpadToggle and call the corresponding XInput2 functions to toggle the state of the touchpad.
Investigating XInput2 was supposed to be the difficult part since it is out of my area of comfort, but at the end it resulted it was not that difficult and the desired effect can be achieved with no more than 10 lines of code.
After getting the correct XInput2 calls I started to build the skeleton of my kded module and when I was going to register the global KAction to listen for XF86XK_TouchpadToggle I realized Qt does not have support for this key, which means I can not use a KAction for that. Sad :-/
This has resulted in my getting diverted from my original goal and writing a patch for Qt5 to support the XF86XK_TouchpadToggle key and two other ones. Sadly this does not solve my immediate itch so I will either live with that itch or try to detect the keypress at the X level, but i'm not sure that's something I want to do :D
Update: I went the X11 way and it was not that painful. I now have some code that works, putting it in a git repo as soon as I get one :-)