Recent window managers have a feature called "focus stealing prevention", which is wonderful in theory. But in practice... well, do a Google search, and see how many people don't like it. The problem is that it's a whole bunch of guesswork, and so it may cause problems when it guesses wrong.
Take, for example, GNUstep applications. GNUstep applications have their menu in a separate window (like on MacOS X), and the menu disappears when the application is inactive. If the application has no other windows, then it tries to give focus to the menu. But then focus stealing prevention kicks in and takes away the focus. The application then detects that it lost focus, deactivates itself, and hides the main menu, making it hard to interact further with the application.
That was the cause for one of the window focusing issues that I was looking at for my GSoC project.
So how do you steal focus and get away with it? Simple: ask nicely first, before you steal. The EWMH spec has an atom called _NET_ACTIVE_WINDOW, which allows windows to request focus. It turns out, if I use that, then steal focus, then the window manager will let me.
However, KWin/KDE (or at least some versions of it) needs a bit more coercing, and we need to set _NET_USER_TIME, while _NET_ACTIVE_WINDOW doesn't seem to do anything.
The final solution:
- set _NET_USER_TIME property
- send _NET_ACTIVE_WINDOW message
- call XSetInputFocus