Instead of relying on release events not getting lost, every event now signals the opponent
to release its pointer grab.
There is one case that requires a Leave event:
Consider a Sending client A and receiving Client B.
If B enters the dead-zone of client A, it will send an enter event towards A but before
A receives the Release event, it may still send additional events towards B that should not cause
B to immediately revert to Receiving state again.
Therefore B puts itself into AwaitingLeave state until it receives a Leave event coming from A.
A responds to the Enter event coming from B with a leave event, to signify that it will no longer
send any events and releases it's pointer.
To guard against packet loss of the leave events, B sends additional enter events while it is in AwaitingLeave
mode until it receives a Leave event at some point.
This is still not resilient against possible packet reordering in UDP but in the (rare) case where a leave event arrives before some other event coming from A, the user would simply need to move the pointer into the dead-zone again.
* macos: initial support
- adapted conditional compilation
- moved lan-mouse socket to ~/Library/Caches/lan-mouse-socket.sock instead of XDG_RUNTIME_DIR
- support for mouse input emulation
TODO: Keycode translation, input capture
