Re: [Qemu-devel] [PATCH v6] ui/cocoa.m: Add ability for user to specify mouse ungrab key

[Gerd Hoffmann]

On Sat, Feb 03, 2018 at 12:17:43PM -0500, John Arbuckle wrote:
> Currently the ungrab keys for the Cocoa and GTK interface are Control-Alt-g.
> This combination may not be very fun for the user to have to enter, so we
> now enable the user to specify their own key(s) as the ungrab key(s). The
> list of keys that can be used is found in the file qapi/ui.json under 
> QKeyCode.
> The max number of keys that can be used is three.
> 
> Syntax: -display cocoa,hotkey-grab=<key-key-key>
> 
> Example usage:  -display cocoa,hotkey-grab=home
>               -display cocoa,hotkey-grab=shift-ctrl
>               -display cocoa,hotkey-grab=ctrl-x
>               -display cocoa,hotkey-grab=pgup-pgdn
>               -display cocoa,hotkey-grab=kp_5-kp_6
>               -display cocoa,hotkey-grab=kp_4-kp_5-kp_6
>               -display cocoa,hotkey-grab=ctrl-alt

Finally found the time for a closer look and some testing.

Problem is the hotkeys are all forwarded to the guest.
So when using -- for example -- the pgup-pgdn hotkey
and you press the combination the guest will see it.

I see basically two options to deal with that:

(a) Make the code more clever.  On pgup keydown event
    the code has to figure this might be part of a hotkey
    sequence, hold back the event to see what comes next.
    - If the next event is pgup keyup -> ok, normal pgup
      keypress, forward both keydown and keyup to the guest.
    - If the next event is pgdn keydown -> hotkey found.
      So do hotkey action, don't forward keydown (and
      following keyup) events to the guest.

(b) Restrict allowed hotkeys to modifier key(s) plus one
    non-modifier key.  Forwarding modifier keydown+keyup
    to the guest has typically effects inside the guest,
    so we only have to hold back that single non-modifier
    key.  That is alot easier to implement.

cheers,
  Gerd