OpenGL key down and key up on CTRL key

Question

I've found a lot of information about using GLUT to detect whether the control key is pressed using the GLUT_ACTIVE_CTRL macro. This macro only works, apparently, within a keyboard or mouse callback function. I need to know whether or not the control key is pressed at a point in my main loop, but GLUT_ACTIVE_CTRL doesn't seem to work in this context.

So, is there a way to detect key up and key down events on the control key (without any other keys being typed) in a platform independent OpenGL-ish way?

EDIT: The keyboard callback is not fired (at least for a default setup) when the control key is pressed. This is the basic problem, that I can only test whether the control key is or isn't pressed when another key is pressed and thus fires the keyboard callback.

My setup is something like:

// ... in main function:
glutKeyboardFunc(keyboard);

//later in the code: 

void keyboard(unsigned char key, int _x, int _y)
{
    printf("keydown \n");

    if (glutGetModifiers() == GLUT_ACTIVE_CTRL) {
            printf("control key is pressed.\n");
    }
    //etc.

When I press any normal character "keydown " is printed to stdout. When I press the ctrl key, nothing happens. If I press ctrl+c, "keydown control key is pressed." is printed.

However, in my main loop I added:

if (glutGetModifiers() == GLUT_ACTIVE_CTRL) {
    printf("Control key down.\n");
} else {
    printf("Control key up.\n");
}

and it always prints "Control key up." regardless of whether I am pressing the control key or not.

Answer 1

In the event handler record the setting of the key. You can then expose that storage to be read from your main loop.

Answer 2

Not using GLUT as specced. You may wish to check out GLFW.