Swapping Menus

GLUT even allows us to change an entire menu in the middle of our application. Two functions are provided: glutSetMenu and glutGetMenu. The syntax for the former is:

void glutSetMenu(int menu);

Parameters:

• menu – the index of a previously created menu

This function allows us to swap a menu, for instance if there is a change in the context of the application.

The syntax for glutGetMenu is as follows:

int glutGetMenu(void);

This function returns the index of the current menu. Next we present an example where we use two menus that are swapped when the user presses F1.

void processSpecialKeys(int c, int x, int y) {

	if (!flag) {
		if (c == GLUT_KEY_F1) {
			int x = glutGetMenu();
			if (x == menu1)
				glutSetMenu(menu2);
			else
				glutSetMenu(menu1);
			// don't forget to attach the menu!!!
			glutAttachMenu(GLUT_RIGHT_BUTTON);
		}
	}
}

void createGLUTMenus() {

	menu2 = glutCreateMenu(processMenuEvents);
	glutAddMenuEntry("Blue",BLUE);
	glutAddMenuEntry("Green",GREEN);
	glutAddMenuEntry("Red",RED);

	menu1 = glutCreateMenu(processMenuEvents);
	glutAddMenuEntry("Red",RED);
	glutAddMenuEntry("Green",GREEN);
	glutAddMenuEntry("Blue",BLUE);
	glutAttachMenu(GLUT_RIGHT_BUTTON);
}