how to determine if CapsLock is on [crossplatform]

[papius_vtualetius]

hi all!
i'll tell you how to determine the state of CapsLock (this code can be modifyed for NumLock/ScrollLock, but you are to do that by yourself)

note: this will work under windows and any system that uses X11.

the function is simple:



bool QMyClass::checkCapsLock()
{
// platform dependent method of determining if CAPS LOCK is on
#ifdef Q_OS_WIN32 // MS Windows version
return GetKeyState(VK_CAPITAL) == 1;
#else // X11 version (Linux/Unix/Mac OS X/etc...)
Display * d = XOpenDisplay((char*)0);
bool caps_state = false;
if (d)
{
unsigned n;
XkbGetIndicatorState(d, XkbUseCoreKbd, &n);
caps_state = (n & 0x01) == 1;
}
return caps_state;
#endif
}


but we must have some includes:



#ifdef Q_OS_WIN32
# include <windows.h>
#else
# include <X11/XKBlib.h>
#endif


to use X11/XKBLib.h, you have to install libx11-dev and link with -lX11

but there are some troubles!

for example, let's see eventFilter:



bool QMyClass::eventFilter(QObject* obj, QEvent* event)
{
if (event->type() == QEvent::KeyPress) {
// ...
}
}


look's good, but won't work under X11:



error: expected token ':' got '2'


why? what happened?
everything is simple. just look at X11/X.h:



[186] #define KeyPress 2


so that's that! we need to #undef those defines that conflicts with QEvent::Type enum:



#ifdef Q_OS_WIN32
# include <windows.h>
#else
# include <X11/XKBlib.h>
# undef KeyPress
# undef KeyRelease
# undef FocusIn
# undef FocusOut
// etc...
#endif


this will make some troubles if you want to use some specific X11 features, but i think if you are using Qt, you don't need that ;]

that's all, see ya =)

PS: sorry for my bad english

[Lesiok]

Just read Qt docs (http://doc.trolltech.com/4.6/qapplication.html#keyboardModifiers)

[MaikoID]

Hi, I've a similar problem. I need to check which is the physical modifiers' positions, Control, Shift and Alt. On Windows I did it handling the winEvents I'm trying to do the same in linunx handling the x11events but I can't check if the current XEvent is a KeyPress event. One of the problems is what you mentioned, I needed to undef the X11 KeyPress macro. I have tried to compare the XEvent type with 2 because this is the constant declared in X11/X.h but didn't work.


maiko@cits-d530:~/Projetos/Positivo$ grep -i keypress /usr/include/X11/X.h
#define KeyPressMask (1L<<0)
#define KeyPress 2

this is my current code


bool MainWindow::x11Event(XEvent *xe)
{
//TODO: remove #undef KeyPress
if(xe->type == 2)
{
switch (xe->xkey.keycode)
{
case 37://Control_L
keyPressEvent(xe->xkey.keycode, "Key_ControlL");
break;
case 105://Control_R
keyPressEvent(xe->xkey.keycode, "Key_ControlR");
break;
case 50://Shift_L
keyPressEvent(xe->xkey.keycode, "Key_ShiftL");
break;
case 62://Shift_R
keyPressEvent(xe->xkey.keycode, "Key_ShiftR");
break;
default:
return false;
}
return true;
}
return false;
}


Bye and thx.

[d_stranz]

Just read Qt docs (http://doc.trolltech.com/4.6/qapplication.html#keyboardModifiers)

Looked at QApplication::keyboardModifiers(). I don't see anything there that you could use to tell the state of the NumLock, CapsLock, or ScrollLock keys. My interpretation of this method is that if I had pressed Shift, Alt, or one of the other modifier keys while pressing another key, this would tell me that. The "Lock" keys are not modifier keys.

[dswartz]

I am also curious about num, scroll, and kana locks. If

XkbGetIndicatorState(d, XkbUseCoreKbd, &n);
caps_state = (n & 0x01) == 1;

will give us caps lock's state, and I know that

num_state = (n & 0x02) == 2;

will give us number lock's state, and I believe that

scroll_state = (n & 0x04) == 4;

should give us the scroll lock's state, but what about Kana lock? 0x08????