bug#14661: 24.3.50; `C-<scroll>' is seen as `C-<pause>'

bug#14661: 24.3.50; `C-<scroll>' is seen as `C-<pause>'

[Drew Adams]

Dunno whether this is an Emacs bug or a keyboard problem.

When I use `C-h k' and then press Control and hit the Scroll Lock key,
Emacs takes that as `C-<pause>', not `C-<scroll>'.  However, every other
combination of a modifier with the Scroll Lock key, and use of no
modifier with it, acts as I would expect: Emacs sees
`<scroll>',`M-<scroll>', `C-M-<scroll>', `C-S-<scroll>', `S-<scroll>',
`M-S-<scroll>', and `C-M-S-<scroll>'.

In GNU Emacs 24.3.50.1 (i686-pc-mingw32)
 of 2013-06-17 on ODIEONE
Bzr revision: 113024 eliz@gnu.org-20130617163040-8hmzci370q4argze
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/Devel/emacs/binary --enable-checking=yes,glyphs
 CFLAGS=-O0 -g3 LDFLAGS=-Lc:/Devel/emacs/lib
 CPPFLAGS=-Ic:/Devel/emacs/include'

bug#14661: 24.3.50; `C-<scroll>' is seen as `C-<pause>'

[Eli Zaretskii]

> Date: Tue, 18 Jun 2013 19:53:02 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> 
> Dunno whether this is an Emacs bug or a keyboard problem.

Neither.

> When I use `C-h k' and then press Control and hit the Scroll Lock key,
> Emacs takes that as `C-<pause>', not `C-<scroll>'.  However, every other
> combination of a modifier with the Scroll Lock key, and use of no
> modifier with it, acts as I would expect: Emacs sees
> `<scroll>',`M-<scroll>', `C-M-<scroll>', `C-S-<scroll>', `S-<scroll>',
> `M-S-<scroll>', and `C-M-S-<scroll>'.

This is a conundrum whose way out I don't know, nor whether it at all
exists.  Windows gives us the same virtual key code VK_CANCEL for both
C-<scroll> and C-<pause> (for reasons of backward compatibility).  We
want to produce a "normal" Ctrl-modified key from this, but we don't
know which one of the two was pressed.  So we arbitrarily choose to
produce C-<pause>.

If someone has a way out of this that doesn't require a complete
rewrite of the keyboard reading code, please speak up.  Otherwise,
this will remain a very distant wishlist.

bug#14661: 24.3.50; `C-<scroll>' is seen as `C-<pause>'

[Juanma Barranquero]

On Wed, Jun 19, 2013 at 4:34 PM, Eli Zaretskii <eliz@gnu.org> wrote:

> This is a conundrum whose way out I don't know, nor whether it at all
> exists.  Windows gives us the same virtual key code VK_CANCEL for both
> C-<scroll> and C-<pause> (for reasons of backward compatibility).

According to this:

http://blogs.msdn.com/b/oldnewthing/archive/2008/02/11/7596539.aspx

there's no way to fix it:

«Even though the enhanced keyboard moved the Pause and Break functions
to their own key, pressing the Pause key internally generated scan
codes that simulated a press of Ctrl+NumLock. In other words, when you
pressed Pause, the keyboard hardware actually tells the computer, "The
user pressed the Ctrl key and then pressed the NumLock key."
Similarly, when you pressed Ctrl+Break, the keyboard hardware tells
the computer, "The user pressed the Ctrl key and then pressed the
ScrollLock key."

Therefore, Ctrl+ScrollLock acts like Ctrl+Break because at the
hardware level, they are the same thing. That the two functions exist
on separate keys is just a fake-out by the keyboard hardware.»

bug#14661: 24.3.50; `C-<scroll>' is seen as `C-<pause>'

[Juanma Barranquero]

On Wed, Jun 19, 2013 at 4:44 PM, Juanma Barranquero <lekktu@gmail.com> wrote:

> there's no way to fix it:

Or perhaps there's one, after all:

http://en.wikipedia.org/wiki/Break_key

«Pressing the dedicated Pause key on 101/102-key keyboards sends the
same scancodes as pressing Ctrl, then NumLock, then releasing them in
the reverse order would do; additionally, an E1hex prefix is sent
which enables 101/102-key aware software to discern the two
situations, while older software usually just ignores the prefix.»

Very distant wishlist, indeed.

bug#14661: 24.3.50; `C-<scroll>' is seen as `C-<pause>'

[Drew Adams]

Thanks to you both for clarifying this (and so promptly).
I'm OK with your closing the bug, or I can do so if you prefer.

I think you're saying that this is a Windows-only problem.
(If not, perhaps it is worth documenting somewhere?)

bug#14661: 24.3.50; `C-<scroll>' is seen as `C-<pause>'

[Juanma Barranquero]

On Wed, Jun 19, 2013 at 4:48 PM, Drew Adams <drew.adams@oracle.com> wrote:

> Thanks to you both for clarifying this (and so promptly).
> I'm OK with your closing the bug, or I can do so if you prefer.

I would suggest closing it.

> I think you're saying that this is a Windows-only problem.

Not Window-specific, it's the keyboard hardware.

> (If not, perhaps it is worth documenting somewhere?)

Don't think so. It is not an Emacs-specific limitation either.

bug#14661: 24.3.50; `C-<scroll>' is seen as `C-<pause>'

[Drew Adams]

> I would suggest closing it.

Done.