glutChangeToMenuEntry changes the specified menu item in the current menu into a menu entry.
void glutChangeToMenuEntry(int entry, char *name, int value);
glutChangeToMenuEntry changes the specified menu entry in the current menu into a menu entry. The entry parameter determines which menu item should be changed, with one being the topmost item. entry must be between 1 and glutGet(GLUT_MENU_NUM_ITEMS) inclusive. The menu item to change does not have to be a menu entry already. The string name will be displayed for the newly changed menu entry. The value will be returned to the menu's callback if this menu entry is selected.