GLUT Menu World

This post demonstrates how to create a GLUT menu and add to it sub-menus and menu items.

In the above sample app, clicking on a menu item in the popup menu will log that menu item’s ID to the console window. Below is the function setupMenus() that creates the main menu and adds to it all the sub-menus and menu items. You can change it based on your needs then call it in the init() method.

//-------------------------------------------------------------------------
//  Set up the GLUT Menus.
//-------------------------------------------------------------------------
void setupMenus ()
{
    int subMenuCount;  //  Count of sub menus
    int menuItemCount; //  Count of menu items in a submenu
    int *menuIds;      //  Submenu IDs
    char str[256];     //  The string of the current menu item
    int i, j;          //  Iterators

    //  Generate a random value for submenu count
    subMenuCount = rand() % 20;

    //  Allocate memory for the submenu IDs
    menuIds = (int *) xmalloc (subMenuCount * sizeof (int));

    //  Create all the sub menus
    for (i = 0; i < subMenuCount; i++)
        menuIds[i] = glutCreateMenu (showMenuItem);

    for (i = 1; i < subMenuCount; i++)
    {
        //  Set sub menu string
        sprintf (str, "SubMenu %d", i);

        //  Add the current submenu to previous submenu
        glutSetMenu (menuIds[i-1]);
        glutAddSubMenu (str, menuIds[i]);

        //  New menu item count for the new submenu
        menuItemCount = rand () % 20;

        //  Add menu items to the current submenu
        for (j = 1; j < menuItemCount; j++)
        {
            sprintf (str, "Menu Item %d", j);
            glutAddMenuEntry (str, j);
        }
    }

    //  Set main menu as the current menu
    glutSetMenu (menuIds[0]);

    //  Attach the menu to the RMB
    glutAttachMenu(GLUT_RIGHT_BUTTON);
}

Major GLUT functions briefly explained:

• glutCreateMenu creates the main menu or sub-menu and returns its ID. It takes as a parameter a pointer to a function with the signature void func (int menuItemId). This function is called every time the  user clicks a menu item in the menu and the parameter menuItemId passed to it represents the id of the menu item.
• glutAddSubMenu adds another menu to current menu.
• glutAddMenuEntry adds a menu item to the current menu.
• glutSetMenu sets the current menu. So when we call glutAddSubMenu or glutAddMenuEntry, they get added to the current menu.
• glutAttachMenu(GLUT_RIGHT_BUTTON) attaches the “current” menu to the right click button. So when you right click the mouse, the popup menu will show up.

This is the function that we are passing to glutCreateMenu in our sample app. Every time the user clicks on a menu item, this function is called and it will simply display the menu item id on the console window.

//-------------------------------------------------------------------------
//  Displays the menu item id on the console window
//-------------------------------------------------------------------------
void showMenuItem (int val)
{
    printf ("Menu Item: %d\n", val);
}

Download the full source code on my GitHub page.