For Xwayland windows we observed that passing pointer focus to another
window does not trigger proper leave events on X. Which results in e.g.
tooltip windows to show after the pointer moved to a completely
different position on a completely different surface.
From an X perspective that's kind of correct: the pointer is still at
the same position and the x11 api to query the cursor position is still
on the last known position passed to Xwayland. Whether this problem can
or should be fixed in Xwayland is not obvious.
To circumvent this problem KWin warps the xcb pointer to 0/0 whever an
X window loses pointer focus. That way the X window gets a proper leave
through the X protocol.
This created a problem though: when giving focus back to the X window it
started to warp the pointer for maximized windows as KWin got pointer
motion events through the X11 event filter for positions on the window
decoration. These are passed into the screen edge filter which pushes
the pointer back and warps our Wayland pointer. To solve this problem
KWin no longer performs any actions for pointer motion in the X11 event
filter if not on X11. The event filter needs to be reworked and most of
it should be moved into the Platform API, if possible.