Open the include folder of your GStudio installation, then open default.c. There you will find def_debug() which is the function in question to show the debug panel.

Your problem may be related to other things, for example when you press Alt+Tab to leave your game, (edit a shader, check your e-mails or whatever) then click your game window again, the engine will think that you are still pressing Alt. As a result, when pressing F11 only the following code will be executed:

Code:
void def_debug() 
{
    beep();
    if(key_alt) 
    { 
        diag_status(); 
        return; 
    }
    ...
}

"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual

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