Building a menu of delegates and enums

I like delegates. I also like enums. Furthermore, I happen to be part of a small group of people who actually enjoy the immediate mode GUI system in Unity. And I want you to like it too

So – menus. After having observed quite a few very funky approaches, in the IRC channel, to building main menu functionality and giving advice in there, I decided to sow together those ideas into a short example.

The main idea here is to be able to build and manage a menu system quickly and easily. This line adds a new submenu to the system – designated MyMenuState and implemented in the OnMyMenuGUI method:

m_Menus [MenuState.MyMenuState] = OnMyMenuGUI;

Notice that since we’re using delegates, the GUI method needn’t be implemented in the same script and could even live on an entirely different GameObject. Why is this so clever (besides enums and delegates being cool)? Because managing and switching between menus set up like this is insanely easy. This is the central GUI method for the menu system:

public void OnGUI ()
{
    m_Menus [m_CurrentState] ();
}

And this is GUI code inside a menu GUI method for switching to a different submenu:

m_CurrentState = GUILayout.Button ("Credits") ? MenuState.Credits : m_CurrentState;

So there. Enough talk. Have some example code:

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class Menu : MonoBehaviour
{
    delegate void OnGUIImplementation();
    public enum MenuState {Main,Settings,Credits};
    public struct Settings
    {
        public bool m_ThisSetting, m_ThatSetting, m_TheOtherSetting;
    };
    static Vector2 m_StandardMenuSize = new Vector2 (200.0f, 300.0f);
    static string m_LogoURL = "http://download.unity3d.com/images/top-menu/mm_unity_icon.png";
    static Texture2D m_Logo = null;

    private MenuState m_CurrentState = MenuState.Main;
    private Dictionary<MenuState, OnGUIImplementation> m_Menus;
    private Settings m_Settings;

    void Awake ()
    {
        m_Menus = new Dictionary<MenuState, OnGUIImplementation> ();
        m_Menus [MenuState.Main] = OnMainMenuGUI;
        m_Menus [MenuState.Settings] = OnSettingsGUI;
        m_Menus [MenuState.Credits] = OnCreditsGUI;
        StartCoroutine (GetLogo ());
    }

    IEnumerator GetLogo ()
    {
        WWW www = new WWW (m_LogoURL);

        yield return www;

        if (www.error == null)
        {
            m_Logo = www.texture;
        }
    }

    public void OnGUI ()
    {
        m_Menus [m_CurrentState] ();
    }

    static void BeginStandardMenu (string title)
    {
        GUILayout.BeginArea (new Rect ((Screen.width - m_StandardMenuSize.x) * 0.5f, (Screen.height - m_StandardMenuSize.y) * 0.5f, m_StandardMenuSize.x, m_StandardMenuSize.y));
            GUILayout.BeginVertical (GUI.skin.GetStyle ("Box"));
                GUILayout.Label (title, GUI.skin.GetStyle ("Box"));
    }

    static void EndStandardMenu ()
    {
        Color color;

                GUILayout.BeginHorizontal ();
                    GUILayout.FlexibleSpace ();
                        color = GUI.color;
                        GUI.color = Color.grey;
                        GUILayout.Label ("My game version 2.4X");
                        GUI.color = color;
                    GUILayout.FlexibleSpace ();
                GUILayout.EndHorizontal ();
            GUILayout.EndVertical ();
        GUILayout.EndArea ();
    }

    void OnMainMenuGUI ()
    {
        BeginStandardMenu ("Main menu");
            if (m_Logo != null)
            {
                GUILayout.BeginHorizontal ();
                    GUILayout.FlexibleSpace ();
                        GUILayout.Label (m_Logo);
                    GUILayout.FlexibleSpace ();
                GUILayout.EndHorizontal ();
            }
            if (GUILayout.Button ("New game"))
            {
                Application.LoadLevel ("Level one");
            }
            m_CurrentState = GUILayout.Button ("Settings") ? MenuState.Settings : m_CurrentState;
            m_CurrentState = GUILayout.Button ("Credits") ? MenuState.Credits : m_CurrentState;
            GUILayout.FlexibleSpace ();
        EndStandardMenu ();
    }

    void OnSettingsGUI ()
    {
        BeginStandardMenu ("Settings");
            m_Settings.m_ThisSetting = GUILayout.Toggle (m_Settings.m_ThisSetting, "This setting");
            m_Settings.m_ThatSetting = GUILayout.Toggle (m_Settings.m_ThatSetting, "That setting");
            m_Settings.m_TheOtherSetting = GUILayout.Toggle (m_Settings.m_TheOtherSetting, "The other setting", GUI.skin.GetStyle ("Button"));
            GUILayout.FlexibleSpace ();
            m_CurrentState = GUILayout.Button ("Main menu") ? MenuState.Main : m_CurrentState;
        EndStandardMenu ();
    }

    void OnCreditsGUI ()
    {
        BeginStandardMenu ("Credits");
            GUILayout.Label ("This game was created by some of the most awesomestest people on the planet. Having failed in their mission to Pluto, they started making games, which - as you can see - resulted in much joy and success!");
                GUILayout.Space (20.0f);
                GUILayout.BeginHorizontal ();
                    GUILayout.FlexibleSpace ();
                        GUILayout.Label ("The awesomestest people inc.");
                GUILayout.EndHorizontal ();

            GUILayout.FlexibleSpace ();
            m_CurrentState = GUILayout.Button ("Main menu") ? MenuState.Main : m_CurrentState;
        EndStandardMenu ();
    }
}

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Example project: Menu.zip – built with Unity 2.6.1