where does Alt become Meta?

where does Alt become Meta?

[Will Parsons]

I use Emacs on a variety of systems and circumstances, and on just about
all of them I'm used to using the Alt key as Meta, so I was surprised 
recently to find that in an Emacs session running on FreeBSD, but accessed
on a Windows system via TightVNC, A-q was unbound.  Esc-q was bound as
expected to fill-paragraph, but since I find the Alt combinations a lot
more convenient, I would like to fix that, but have no idea where to look.
Where does Emacs map Alt combinations to Meta combinations?

- Will

Re: where does Alt become Meta?

[Eli Zaretskii]

> From: Will Parsons <oudeis@nodomain.invalid>
> Date: 20 Jul 2007 21:06:00 GMT
> 
> I use Emacs on a variety of systems and circumstances, and on just about
> all of them I'm used to using the Alt key as Meta, so I was surprised 
> recently to find that in an Emacs session running on FreeBSD, but accessed
> on a Windows system via TightVNC, A-q was unbound.

I think you might be confusing two different issues: Emacs does
recognize an Alt prefix, and it is different from the Meta prefix.
A-q is always unbound in Emacs by default.

> Where does Emacs map Alt combinations to Meta combinations?

Nowhere.  This is done outside Emacs's keymaps.  In your case, you
should set up TightVNC to send the Meta modifier when you press the
Alt key.

Re: where does Alt become Meta?

[Johan Bockgård]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Will Parsons <oudeis@nodomain.invalid>
[...]
> I think you might be confusing two different issues: Emacs does
> recognize an Alt prefix, and it is different from the Meta prefix.
> A-q is always unbound in Emacs by default.

Emacs only recognizes Alt if there is a separate Meta.

>> Where does Emacs map Alt combinations to Meta combinations?
>
> Nowhere.  This is done outside Emacs's keymaps.

Unless there are Meta keys, Emacs reinterprets Alt as Meta.

  [xterm.c]

  /* If we couldn't find any meta keys, accept any alt keys as meta keys.  */
  if (! dpyinfo->meta_mod_mask)
    {
      dpyinfo->meta_mod_mask = dpyinfo->alt_mod_mask;
      dpyinfo->alt_mod_mask = 0;
    }

  /* If some keys are both alt and meta,
     make them just meta, not alt.  */
  if (dpyinfo->alt_mod_mask & dpyinfo->meta_mod_mask)
    {
      dpyinfo->alt_mod_mask &= ~dpyinfo->meta_mod_mask;
    }


cf. http://www.emacswiki.org/cgi-bin/wiki/MetaKeyProblems

-- 
Johan Bockgård

Re: where does Alt become Meta?

[Eli Zaretskii]

> From: bojohan+news@dd.chalmers.se (Johan =?utf-8?Q?Bockg=C3=A5rd?=)
> Date: Sun, 22 Jul 2007 02:16:43 +0200
> 
> >> Where does Emacs map Alt combinations to Meta combinations?
> >
> > Nowhere.  This is done outside Emacs's keymaps.
> 
> Unless there are Meta keys, Emacs reinterprets Alt as Meta.
> 
>   [xterm.c]

xterm.c is a low-level infrastructure, below the Emacs keymap
machinery.

Anyway, the OP uses VNC on Windows, where there's no separate Meta
key.  So I don't think the cited fragment from xterm.c applies.

Re: where does Alt become Meta?

[Will Parsons]

Eli Zaretskii wrote:
>> From: Will Parsons <oudeis@nodomain.invalid>
>> Date: 20 Jul 2007 21:06:00 GMT
>> 
>> I use Emacs on a variety of systems and circumstances, and on just about
>> all of them I'm used to using the Alt key as Meta, so I was surprised 
>> recently to find that in an Emacs session running on FreeBSD, but accessed
>> on a Windows system via TightVNC, A-q was unbound.
> 
> I think you might be confusing two different issues: Emacs does
> recognize an Alt prefix, and it is different from the Meta prefix.
> A-q is always unbound in Emacs by default.
> 
>> Where does Emacs map Alt combinations to Meta combinations?
> 
> Nowhere.  This is done outside Emacs's keymaps.  In your case, you
> should set up TightVNC to send the Meta modifier when you press the
> Alt key.

Thanks.  I found the right way to configure TightVNC to set Alt to Meta.
I thought that Emacs must handle Alt somehow, since I can use Alt combos
on the console too, but I guess that the console driver handles it somehow?

- Will

Re: where does Alt become Meta?

[Eli Zaretskii]

> From: wbp@nodomain.invalid (Will Parsons)
> Date: 23 Jul 2007 13:52:15 GMT
> 
> I thought that Emacs must handle Alt somehow, since I can use Alt combos
> on the console too, but I guess that the console driver handles it somehow?

Either the console driver or the low-level code in Emacs that has
intimate knowledge of the console behavior and keyboard.