Godot-proposals: Add a way to differentiate Left and Right Shift, Alt, and Control keys

[krscott]

Describe the project you are working on:
A pinball-style game with left and right flippers.

Describe the problem or limitation you are having in your project:
I would like the option of using the left and right Shift keys as left and right paddles for users with tenkeyless or shorter keyboards, however, the Input Map treats these keys both as "Shift", and the InputEventKey scancode is 16777237 for both keys.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
If there was a way to differentiate left and right Shift keys, it would be possible to use these keys for separate functions.

Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:
I can imagine two ways to solve this issue:

1. Add KEY_RIGHT_SHIFT, KEY_RIGHT_ALT, KEY_RIGHT_CONTROL to the KeyList enum.

func _input(ev):
  if ev is InputEventKey:
    match ev.scancode:
      KEY_SHIFT:
        print("left shift")
      KEY_RIGHT_SHIFT:
        print("right shift")

1. Add a location field to InputEventKey with a new enum for left/right. This would preserve the current functionality of KEY_SHIFT, etc., but probably would require more changes to get working with the Input Map menu.

func _input(ev):
  if ev is InputEventKey and ev.scancode == KEY_SHIFT:
    match ev.location:
      MULTIKEY_LOCATION_LEFT:
        print("left shift")
      MULTIKEY_LOCATION_RIGHT:
        print("right shift")

If this enhancement will not be used often, can it be worked around with a few lines of script?:
I'm not aware of any possible way to work around this issue in GDScript.

Is there a reason why this should be core and not an add-on in the asset library?:
This feature would require adding to the GlobalScope KeyList enum or adding an enum to InputEventKey.

[KoBeWi]

The first solution is better and 4.0 is a good chance to add it.
Someone already made an attempt to implement this: https://github.com/godotengine/godot/pull/27991

[bojidar-bg]

Note: As implementing (1) will definitely break compatibility, there is no point in leaving a constant named KEY_SHIFT, instead both constant names should include the location, as in KEY_LEFT_SHIFT and KEY_RIGHT_SHIFT.

[TheDuriel]

There should be all three, KEY_SHIFT, left, and right.
Otherwise you are asking people to do redundant work when they want to use shift, and not a specific side.

(Thus _would_ mean that pressing shift emitts two events, not just one. But that should be fine.)

Also, if any of this is done for shift. It needs to be done for CTL, ALT and mac/win keys as well.

[krscott]

@TheDuriel This would require more work for other cases, though. For instance, an in-game menu that asks a user for a keybinding would need to handle every possible case of double-events, whereas now it only needs to save the scancode. I think that most use cases where the code doesn't care which modifier key is for handling combos (e.g. Ctrl+S), but this would still be possible by reading the modifier value in InputEventWithModifiers.

Maybe these new behaviors could be configurable in the project settings and just let the author decide if they want separate LEFT/RIGHT scancodes or not.

[TheDuriel]

I don't see how this would require more work. Right now the proposal is to split them anyways, and make treating them generally impossible.

What I'm proposing that we let BOTH happen. Pressing a modifier sends the modifer key, and the left or right variant. One press, two events. No compatibility problems.