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CBell

OpenGL Adding Menus

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CBell    122
I'm making an OpenGL program for one of my classes, and the prof wants us to add a menu to it. His requirement is: "Function main should call a function that creates the menu (by calling glutCreateMenu, glutAddMenuEntry, and glutAttachMenu) and registers a callback for the keypresses with glutKeyboardFunc (in addition to the mouse callback). The keyboard callback function should simply call the menu callback function." but if I have a menu function called by glutKeyboardFunc() then the values passed to it will be unsigned char, int, int. And I can't call any outside functions from it for glutCreateMenu(), and glutCreateMenu() would pass it an int. In other words, this:
void menu(unsigned char key, int x, int y)
{
    ...//switch case for keypresses...?

    glutCreateMenu(menu);
    glutAddMenuEntry("star/stop", 1);
    glutAddMenuEntry("slow", 1);
    glutAddMenuEntry("med", 2);
    glutAddMenuEntry("fast", 3);
    glutAddMenuEntry("exit", 2);
    glutAttachMenu(GLUT_RIGHT_BUTTON);
}

int main (int argc, char** argv)
{
    ...//needed code, like glutInit and so on...

    glutKeyboardFunc(menu);

    ...//rest of code, like glutMainLoop etc...

}
would not work. And if I changed the menu callback to something else, like glutCreateMenu(makeMenu) then it wouldn't work since makeMenu(int) would be out of scope. The whole "Function main should call a function that creates the menu" thing is throwing me off as everything that I have seen that has a menu in it has glutCreateMenu(), glutAddMenuEntry(), and glutAttachMenu() in main, and not it's own function. Anybody have any idea? This part of the assignment is really confusing me. *scratches head* lol.

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V-man    813
If you download GLUT demos, there are always examples of this.
You need to changed
void menu(unsigned char key, int x, int y)
to
void menu()

and in main, call menu() to create the menu.

Also call
glutKeyboardFunc(OnKeyboard);

The program a keyboard handler
void OnKeyboard(unsigned char key, int x, int y)
{
switch(key)
{
case 0:
......
}

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CBell    122
Ok. I don't know if this is what he is looking for, but this is what I did, and it works. I've only added the exit command so far, but the others would work the same way. Thought I'd share:


void menu(int);

void menu(int n = -1)
{
switch (n)
{
case 1:
break;
case 2:
break;
case 3:
break;
case 4:
break;
case 5:
exit(0);
break;
default: break;
}
glutCreateMenu(menu);
glutAddMenuEntry("start/stop", 1);
glutAddMenuEntry("slow", 2);
glutAddMenuEntry("med", 3);
glutAddMenuEntry("fast", 4);
glutAddMenuEntry("exit", 5);
glutAttachMenu(GLUT_RIGHT_BUTTON);
}

void key(unsigned char key, int x, int y)
{
switch (key){
case 27:
menu(5);
break;
default:
break;
}
}

int main(int argc, char** argv)
{
...//needed things, yada yada yada
menu();
glutKeyboardFunc(key);
...//needed things, blah blah blah
}


Is there anything inherently wrong with this, or is it ok? It works, so if nobody says anything I'm gonna keep it like this, lol.

Thanks for the help, too.

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Gage64    1235
You don't need to call the menu creation functions each time you handle a key press.

You really need two functions: One that will setup the menu, and another that will handle key presses. The first should be called once inside main(), and the second should be called from key(). This will also remove the need for the default argument.

BTW, notice that when the function argument has it's default value, one thing happens, and when it doesn't, another thing happens. That's usually a sign that your function should really be split into two functions (as is the case here).

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