macOS: Command key intercepted by Java menu accelerators, cannot be sent to VNC session as Meta/Alt

[John Ruttenberg]

 Environment:    
  - TurboVNC Viewer v3.3 (build 20260206), macOS, connecting to TurboVNC 3.3 server on Ubuntu 20.04
  - Mac display: 3840x2160
  - Full-screen mode with -DesktopSize Auto -Tunnel

  Problem:

  On macOS, the Command key is intercepted by Java's menu accelerator system before TurboVNC's keyboard handling can
  process it. This means Command-key combinations are never sent to the VNC session.

  This is a blocker for emacs users on macOS who rely on Command as Meta (e.g., Cmd-X for M-x). This is the standard
  muscle memory for Mac emacs users ? in many cases, decades of it.

  Specific issues:

  1. Cmd-X triggers "Tile All Viewer Windows" instead of sending Meta-X to the VNC session. This is in the Connection
  menu.
  2. GrabKeyboard=Always does not help ? Java intercepts Cmd before the grab takes effect.
  3. NoHotkeys=1 does not help ? menu accelerators are separate from TurboVNC's hotkey system.
  4. Other VNC viewers (e.g., RealVNC Viewer) handle this correctly, sending Command as Alt/Meta to the VNC session.

  Expected behavior:

  When the viewer window is focused (especially in full-screen mode), Command-key combinations should be sent to the VNC
  session as Alt/Meta, not consumed by the viewer's Java menu bar. At minimum, there should be a configuration option to
  control this behavior.

  Workaround attempted:

  Karabiner-Elements can remap Command to Option at the OS level per-application, but requiring a third-party kernel
  extension to work around a key mapping issue is not ideal.

[DRC]

There is a separate parameter (NoMacHotkeys) for disabling the macOS menu accelerators.  Referring to https://github.com/TurboVNC/turbovnc/issues/162, this takes care of all of the Command- key combinations except for:

Command-Q
Command-Comma
- If such is desired, I can probably intercept and transmit these as well whenever NoMacHotkeys is set.

Command-Space
- This can be disabled under System Settings-->Keyboard-->Keyboard Shortcuts-->Spotlight.

Command-Tab
Command-H
- Not much I can do about these without extending the TurboVNC Viewer's keyboard grabbing feature to macOS, and thus far my attempts at that have been unsuccessful.  (Refer also to https://github.com/TurboVNC/turbovnc/issues/162.)

DRC

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[John Ruttenberg]

Command-Q would be especially good to intercept.  It's an emacs keybinding from when dinosaurs ruled the earth.  Command-H is very unfortunate.  It's also an ancient emacs keybinding.

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[DRC]

It is possible to remap the accelerator in System Settings-->Keyboard-->Keyboard Shortcuts-->App Shortcuts.  (Add TurboVNC Viewer as an app, "Hide VncViewer" as a menu title, then select a key combination other than Command-H.)  In practice, however, this doesn't prevent macOS from intercepting Command-H.  :(  macOS keyboard grabbing is the best solution, but I spent a lot of time trying to figure it out and failed.  The TigerVNC Viewer has such a feature, but porting their implementation into the TurboVNC Viewer didn't work for some reason.  If someone else wants to look into it, I'm happy to share my progress so far.

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[John Ruttenberg]

I could not even find TurboVNC Viewer in the applications list for keyboard app shortcuts.

[DRC]

You have to click "Other" and select it manually.  Maybe the problem is that it needs to register itself with the operating system in some way, but I have no idea how to do that.

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