Re: Physical keyboard events

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 29 Oct 2024 16:07:16 +0100
> Cc: emacs-devel@gnu.org
> From: Cecilio Pardo <cpardo@imayhem.com>
> 
> On 29/10/2024 14:40, Eli Zaretskii wrote:
> 
> >> I'm planning to implement physical key press/release events for emacs.
> >> I would add a new element to 'enum event_kind', that in turn would
> >> send a new input event. This input event will be bound in
> >> 'special-event-map' so that it will not modify the normal flow of
> >> keyboard input. Platform dependent code would send these events
> >> on key press and release.
> > 
> > I hope these new events will not be sent at all times, only when some
> > optional variable is set (similar to track-mouse, perhaps).  I
> > wouldn't want Emacs to start processing press/release events on Shift
> > or Ctrl unless a Lisp program needs that, and I don't think we want to
> > change our processing of keyboard such that instead of a single
> > keypress with modifiers we need to process multiple key-press and
> > key-release events when the user simply types on the keyboard.
> 
> Thats why the events will be bound in special-event-map. Nobody will see 
> them, except for the code that handles them.  We can of course 
> completely disable them with a variable.

Even if no one sees them, bombarding the Emacs event queue with
useless events will have its effect: Emacs will become more sluggish,
some while-no-input loops will unexpectedly exit just because the user
happened to touch the Shift key for some reason, etc.

> > Physical keys also raise the issue of supporting input methods,
> > keyboard layout switches, etc.
> 
> I will define a list of keys: LeftShit, RightShift, LeftControl, etc. 
> The platform dependent code will decide which one was pressed. As events 
> will be invisible, I don't think we will interfere with input methods.

I meant the non-modifier keys.  When some OS feature redefines a key,
low-level events will not know that, and will still consider the key
labeled 'a' as 'a', even though I might have switched the keyboard to
another language, where the key labeled 'a' actually produces a
completely different character, say, 'ש'.

> > However, on what systems and which Emacs configurations will it be
> > possible to provide such a feature?
> 
> I think all GUI systems can use this.

So X (with or without any toolkit we support), PGTK, MS-Windows, and
macOS -- all those let applications access low-level key events?