Windows-style `LevelThree` as `Ctrl+Alt`

[wismill]

On Windows the default third-level modifier is actually Ctrl+Alt, while Linux has a dedicated modifier: LevelThree.

While most people would probably use only the AltGr key as third-level modifier, some prefer to use the key combination Ctrl+Alt, either because they do have symmetric Alt keys or because they simply expect AltGr and Ctrl+Alt key combos to be strictly equivalent.

See some use cases on the xkeyboard-config project:

• xkeyboard-config#33
• xkeyboard-config#482
• xkeyboard-config#555

[wismill]

My initial idea to tackle this is to implement a dedicated mechanism:

• Active only on keys that have a key type such that its mask:

  • has LevelThree
  • has at most one of Control or Alt

  The reasoning should be on the modifier encodings.

• Active only when Ctrl+Alt is in the effective modifier mask.

• Generate a sequence of 3 events, similar to RedirectKey():

  1. Save the state; remove Ctr+Alt from the modifiers and add LevelThreee and send the corresponding event.
  2. Send the key event.
  3. Restore the state and send the corresponding event.