Capturing alt-tab event

[billconan]

I want to capture alt-tab event, so that my program will not be switched to other programs, as long as my program is under focus.

to do this, I need to capture the alt-tab event. I'm using nativeEventFilter, but I don't know which native event I need to capture (I'm working on windows, but eventually I need to support linux and mac also).

I tried WM_KEYUP and WM_SYSKEYUP. they won't work.

is there a ALT_TAB event I can capture? or is there any other tricks I can play?

I know that virtual box supports this and its ui seems to be in Qt.

[billconan]

so far haven't found how to achieve this on windows.
this link suggests unregistering the default windows hotkey, but this method won't work on win7 and win8
http://www.codeguru.com/cpp/misc/misc/keyboard/article.php/c433/Disabling-the-AltTab-key-combination.htm

this method looks promising, but requires more code change in the client:
http://stackoverflow.com/questions/11352343/how-can-i-disable-specific-windows-hotkeys-from-inside-a-software-using-c

[billconan]

method mentioned here should work for windows.
http://www.windowsnetworking.com/kbase/WindowsTips/WindowsNT/AdminTips/Miscellaneous/DisableAltTab.html

but I don't know how to do this on mac and linux. need to dig more.

[billconan]

I have successfully captured cmd+tab on mac by using Quartz event service, but there are two serious problems.

http://brianlipkowitz.tumblr.com/post/4881199383/quartz-event-taps

first, the user must run with root privilege. for users without CS background, this could be a bit difficult.

second, the method monitors the key events sent to the entire system. the implementation has to be careful in order to not to break other apps.

[billconan]

ok, I installed virtualbox, and found out that it doesn't seem to require root user to capture alt-tab.

after digging the source code, it seems that they achieved this by disabling default hotkeys.

I need to experiment this myself.

@
/**

• Disables or enabled global hot keys.

• @param fDisable Pass 'true' to disable the hot keys, pass 'false' to re-enable them.
  */
  void DarwinDisableGlobalHotKeys(bool fDisable)
  {
  static unsigned s_cComplaints = 0;

  /*

  • Lazy connect to the core graphics service.
    */
    if (!g_fConnectedToCGS)
    {
    g_CGSConnection = _CGSDefaultConnection();
    g_fConnectedToCGS = true;
    }

  /*

  • Get the current mode.
    */
    CGSGlobalHotKeyOperatingMode enmMode = kCGSGlobalHotKeyInvalid;
    CGSGetGlobalHotKeyOperatingMode(g_CGSConnection, &enmMode);
    if ( enmMode != kCGSGlobalHotKeyEnable
    && enmMode != kCGSGlobalHotKeyDisable
    && enmMode != kCGSGlobalHotKeyDisableExceptUniversalAccess)
    {
    AssertMsgFailed(("%d\n", enmMode));
    if (s_cComplaints++ < 32)
    LogRel(("DarwinDisableGlobalHotKeys: Unexpected enmMode=%d\n", enmMode));
    return;
    }

  /*

  • Calc the new mode.
    */
    if (fDisable)
    {
    if (enmMode != kCGSGlobalHotKeyEnable)
    return;
    enmMode = kCGSGlobalHotKeyDisableExceptUniversalAccess;
    }
    else
    {
    if (enmMode != kCGSGlobalHotKeyDisableExceptUniversalAccess)
    return;
    enmMode = kCGSGlobalHotKeyEnable;
    }

  /*

  • Try set it and check the actual result.
    /
    CGSSetGlobalHotKeyOperatingMode(g_CGSConnection, enmMode);
    CGSGlobalHotKeyOperatingMode enmNewMode = kCGSGlobalHotKeyInvalid;
    CGSGetGlobalHotKeyOperatingMode(g_CGSConnection, &enmNewMode);
    if (enmNewMode != enmMode)
    {
    / If the screensaver kicks in we should ignore failure here. */
    AssertMsg(enmMode == kCGSGlobalHotKeyEnable, ("enmNewMode=%d enmMode=%d\n", enmNewMode, enmMode));
    if (s_cComplaints++ < 32)
    LogRel(("DarwinDisableGlobalHotKeys: Failed to change mode; enmNewMode=%d enmMode=%d\n", enmNewMode, enmMode));
    }
    }
    @

[billconan]

I verified that the above code could work, but it uses undocumented apis from the coregraphics framework:

it turned out that they disabled the system default hotkeys by using undocumented hidden apis from the coregraphics framework.

extern "C" {
CGSConnection _CGSDefaultConnection(void);
CGError CGSGetGlobalHotKeyOperatingMode(CGSConnection Connection, CGSGlobalHotKeyOperatingMode *enmMode);
CGError CGSSetGlobalHotKeyOperatingMode(CGSConnection Connection, CGSGlobalHotKeyOperatingMode enmMode);
}

[billconan]

just tested virtual box's solution for linux:

XGrabKey(QX11Info::display(), AnyKey, AnyModifier, w.winId(), False, GrabModeAsync, GrabModeAsync);

works like a charm