Status of modifier keys (shift/ctrl/alt)

[Gautier de Montmollin]

Hello!

I am developing a game / navigation framework (*) using GLUT and now
FreeGLUT.
Everything is fine, there is just an annoying detail: the change of status
in modifier keys (shift/ctrl/alt) is noticed only when something else
happens (other keys, or mouse event).
If I call glutGetModifiers from glutDisplayFunc or glutIdleFunc I get this
message on the console (as well as nasty effects):

GLUT: Warning in .\GLOBE_3D_Demo.exe: glutCurrentModifiers: do not call
outside
core input callback.

So, my question: how to get a fresh status of these modifier keys,
independently of the other keys or the mouse ?

Or, is there a new callback function (say, KeyboardModifierFunc) to add to
the wish list ?

TIA - cheers!
Gautier
__
(*) It is called GLOBE_3D, URL:
http://homepage.sunrise.ch/mysunrise/gdm/g3d.htm

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[steve-72]

Gautier de Montmollin wrote:

> So, my question: how to get a fresh status of these modifier keys,
> independently of the other keys or the mouse ?

No - you can't.  That's actually an operating system restriction
under some OS's - so to be portable, GLUT (and therefore freeglut)
doesn't let you read the modifier keys outside of the mouse and
keyboard callbacks.

The reason is that these are MODIFIER keys - they MODIFY the function
of other keys or of the mouse - so it doesn't make sense to read them
other than when other keys/mouse are doing something.

> Or, is there a new callback function (say, KeyboardModifierFunc) to add to
> the wish list ?

Nope - not going to happen because it's not possible for such functions
to be portable.

Sorry!

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[Bill Kelly]

From: "steve" <sjbaker1@...>

>
> Gautier de Montmollin wrote:
>
>> So, my question: how to get a fresh status of these modifier keys,
>> independently of the other keys or the mouse ?
>
> No - you can't.  That's actually an operating system restriction
> under some OS's - so to be portable, GLUT (and therefore freeglut)
> doesn't let you read the modifier keys outside of the mouse and
> keyboard callbacks.
>
> The reason is that these are MODIFIER keys - they MODIFY the function
> of other keys or of the mouse - so it doesn't make sense to read them
> other than when other keys/mouse are doing something.

Sorry for my n00b question - but to clarify: Does that mean
one can't get an event for the modifier keys themselves?
Like, let's say I wanted to bind "left-shift" to make my
character walk instead of run while the left shift key
is pressed.  I want to detect that press/release regardless
of whether other keys are pressed.  Are you implying that
wouldn't be possible, or have I misunderstood?


Thanks!

Bill



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[steve-72]

Bill Kelly wrote:

> Sorry for my n00b question - but to clarify: Does that mean
> one can't get an event for the modifier keys themselves?

Right - there is no X-windows event for one of those keys
changing state.

> Like, let's say I wanted to bind "left-shift" to make my
> character walk instead of run while the left shift key
> is pressed.

You mean that (say) you hold down the left arrow key to
make your character walk to the left - then while the arrow
key is held down, you push the shift key to turn walking
left into running left?

If that's what you mean then that's OK because you get an
event for the arrow key whenever it is pressed or if it changes
from being 'Left arrow' to 'Shifted left arrow'. Once inside
the GLUT key event callback, you can test the status of the
shift key...no problem there.  Ditto with CTRL and ALT.

If, however, you wanted to fire a gun every time the shift
key was pressed (even when no other keys are held down)
then that would be a major problem.

> I want to detect that press/release regardless
> of whether other keys are pressed.  Are you implying that
> wouldn't be possible, or have I misunderstood?

No - that's impossible (in a portable manner at least).


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[Bill Kelly]

From: "steve" <sjbaker1@...>

>
> If, however, you wanted to fire a gun every time the shift
> key was pressed (even when no other keys are held down)
> then that would be a major problem.
>
>> I want to detect that press/release regardless
>> of whether other keys are pressed.  Are you implying that
>> wouldn't be possible, or have I misunderstood?
>
> No - that's impossible (in a portable manner at least).

Whoa.  I had no idea.

Now I wonder how Quake2 is implemented on Linux.

I just chatted with a Linux Q2 engine developer, who
confirmed that Q2 does run under X, and, it does
receive independent events for the shift / alt keys,
even if no other keys are pressed.

He suggested I run `xev`, an event reporting tool for
X, saying that he also gets independent shift and alt
key events there.
(I don't have a linux box with X installed at present,
so I couldn't try it personally.)

So I guess the question is, do `xev` and Quake2 get
their events in some non-portable fashion... I dunno.
:-(

(I'll be interested to see what SDL does, as well...
I wouldn't harp on the matter, except I was planning
to be able to bind the modifier keys in my FreeGLUT
app, as they can be in Q2...)


Regards,

Bill



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[Bill Kelly]

From: "Bill Kelly" <billk@...>
>
> Now I wonder how Quake2 is implemented on Linux.
>
> I just chatted with a Linux Q2 engine developer, who
> confirmed that Q2 does run under X, and, it does
> receive independent events for the shift / alt keys,
> even if no other keys are pressed.

Just an addendum, for what it's worth: He pointed me
at the code, where the x11 keys are being translated
into values quake likes.  
(Line 436 is handling left/right shift.)
http://jdolan.dyndns.org/trac/browser/quetoo/src/vid_glx.c#L436



Regards,

Bill



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[steve-72]

Bill Kelly wrote:

> Now I wonder how Quake2 is implemented on Linux.

Not portably I suspect!

I confess I'm not 100% clear on where the problems
lie - but having talked this over with Mark Kilgard
(who wrote the original GLUT) some years ago, I was
convinced that GLUT's design is good in this regard.

At any rate, I'm highly resistant to adding significant
features to freeglut.  It's supposed to be a GLUT clone
and that's that.  If you need more features, there are
MUCH better libraries out there.

Personally - I think that game designers should either
go with SDL (if you need more sophistication) - or
with something yet simpler and easier to use than
GLUT such as the PW library that comes with PLIB.

freeglut is here to provide an opensourced way to
deliver OpenGL demos and sample programs - and as
a lingua franca between developers when providing
little programs to show small features or to report
bugs.  In order to fit into that niche, freeglut
needs to be as GLUT-compatible as it can be and
adding more features can only make it harder to
maintain and risk a loss of that vital compatibility.



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[Bill Kelly]

From: "steve" <sjbaker1@...>

>
> At any rate, I'm highly resistant to adding significant
> features to freeglut.  It's supposed to be a GLUT clone
> and that's that.  If you need more features, there are
> MUCH better libraries out there.
>
> Personally - I think that game designers should either
> go with SDL (if you need more sophistication) - or
> with something yet simpler and easier to use than
> GLUT such as the PW library that comes with PLIB.

I see.  OK.  Actually I wanted to use SDL, but the problem
with SDL (and apparently also PW) is that they allow only
a single OpenGL window per process.

I'm not writing a game per se; more of a game-flavored
peer-to-peer 3D browser of sorts, which will need multiple
windows open.

Thanks for the pointer to PLIB, though - that looks quite
nice!

Hmm... Looking at the web page for PLIB::PUI, I see it
allows PU_USE_FLTK .... ?  It would seem FLTK is likely
to allow opening multiple OpenGL windows; however I can't
guess yet how it might behave with regard to modifier
keys.  <grin>


Oh well, I'll keep looking.  Thanks for the info.


Regards,

Bill



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[Bram Stolk-2]

steve wrote:
> Bill Kelly wrote:
>
>> Sorry for my n00b question - but to clarify: Does that mean
>> one can't get an event for the modifier keys themselves?
>
> Right - there is no X-windows event for one of those keys
> changing state.

Yes there is.
You get a KeyPress/KeyRelease event if you press or release Shift, or Ctrl,
or any other key.

You can test this very easily: start up 'xev' (comes standard with x11)
and press the Shift key. You will see the generated event on stdout.

I once hacked in better key handling support in glut, because I
was annoyed by the fact that I could not, e.g. use the default
Quake key 'Ctrl' which is fire, in my own programs.
Unfortunately, this was a x11-only hack, so completely non-portable.

In short, my hack came down to something like this:
< #ifndef NO_BRAM_HACK
<         /* This section was added by Bram Stolk (bram.s at chello.nl) */
<         /* to accomodate a complete keypress detection of */
<         /* all keys known to x11. We will avoid GLUT_KEY_XXX */
<         /* usage, by using the X11 key description. */
<         if (window->x11_keyboard)
<         {
<           KeySym ks;    /* x11 key symbol */
<           char *desc;   /* a descriptive string for the key */
<  
<           ks = XLookupKeysym((XKeyEvent *) & event, 0);
<           desc = XKeysymToString(ks);
<           window->x11_keyboard(desc, (event.type == KeyPress));
<         }
< #endif

This enabled me to detect a press or release of all 101 keys on my keyboard.
Even the weird windows key, and a 'menu' key :-)

   Bram


--
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"Windows is a 32-bit extension to a 16-bit graphical shell for an 8-bit
 operating system originally coded for a 4-bit microprocessor by a 2-bit
 company that can't stand 1 bit of competition."

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[Gautier de Montmollin]

[X-Window - portability - modifier key event]

So there is some hope...

Even if it is not portable, why not something like:
KeyboardModifierEventsAvailable
- gives True or False to inform the program of availability on target system
KeyboardModifierFunc
- get modifier key events
If the KeyboardModifierFunc is erroneously set up on a system where it
cannot work, FreeGLUT could issue a warning like the one issued when calling
GetModifiers outside input callbacks.

And no thank you for SDL...

Gautier

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[Larry E. Ramey]

Some parts of this message have been removed. Learn more about Nabble's security policy.

I'm with Bram on this. We can do it in X11. We can do it in Windows. (Otherwise CounterStrike would not work) Mac-X is based on FreeBSD and I'd bet you 50$ we can do it there.

Maybe there wasn't an X event back in 1992 (I'm making that date up) when GLUT was first coded up, but there sure is now.

Is there any reason besides stubborness not to send the Meta keys to the user?


Add GLUT_KEY_SHIFT, GLUT_KEY_ALT, GLUT_KEY_META1, GLUT_KEY_META2 or whatever...  ON my Linux box, the "windows" button fires off as keycode=115

This is not all that hard to do.

Larry E. Ramey.

(Hey Bram! Still plugging away at SARA I see.... would you believe I have the performer archives open to one of your old questions about pfTexture? Of course you didn't get an answer either.....)

----- Original Message ----
From: Bram Stolk <bram@...>
To: FreeGLUT developers list <freeglut-developer@...>
Sent: Wednesday, October 25, 2006 3:01:26 AM
Subject: Re: [Freeglut-developer] Status of modifier keys (shift/ctrl/alt)

steve wrote:
> Bill Kelly wrote:
>
>> Sorry for my n00b question - but to clarify: Does that mean
>> one can't get an event for the modifier keys themselves?
>
> Right - there is no X-windows event for one of those keys
> changing state.

Yes there is.
You get a KeyPress/KeyRelease event if you press or release Shift, or Ctrl,
or any other key.

You can test this very easily: start up 'xev' (comes standard with x11)
and press the Shift key. You will see the generated event on stdout.

I once hacked in better key handling support in glut, because I
was annoyed by the fact that I could not, e.g. use the default
Quake key 'Ctrl' which is fire, in my own programs.
Unfortunately, this was a x11-only hack, so completely non-portable.

In short, my hack came down to something like this:
< #ifndef NO_BRAM_HACK
<         /* This section was added by Bram Stolk (bram.s at chello.nl) */
<         /* to accomodate a complete keypress detection of */
<         /* all keys known to x11. We will avoid GLUT_KEY_XXX */
<         /* usage, by using the X11 key description. */
<         if (window->x11_keyboard)
<         {
<           KeySym ks;    /* x11 key symbol */
<           char *desc;   /* a descriptive string for the key */
<  
<           ks = XLookupKeysym((XKeyEvent *) & event, 0);
<           desc = XKeysymToString(ks);
<           window->x11_keyboard(desc, (event.type == KeyPress));
<         }
< #endif

This enabled me to detect a press or release of all 101 keys on my keyboard.
Even the weird windows key, and a 'menu' key :-)

   Bram


--
Bram Stolk, VR Engineer SARA, Amsterdam.   tel [phone]

"Windows is a 32-bit extension to a 16-bit graphical shell for an 8-bit
operating system originally coded for a 4-bit microprocessor by a 2-bit
company that can't stand 1 bit of competition."

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