How to create mod for unity game

From Nexus Mods Wiki
Revision as of 13:44, 21 February 2019 by Newman55 (talk | contribs) (How to create a mod for unity game)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

Introduction

To begin with, these mods are more focused on creating scripts than content. But still make a new game object or texture, you can. Unity works on the csharp language, so creating a mod may seem hardcore, but you do not need to be a super programmer, it is enough to know the basic knowledge of programming. It will be even more difficult to dig into the game code in search of the necessary game functions.

Project creation

  1. Download and install Microsoft Visual Studio Community 2017 with C#
  2. Open the project creation and select 'Class Library (NET Framework)'. Change name to 'TestMod'. Open the project properties and target platform should be 'Net Framework 3.5' or 'Net Framework 4.0' for the newer Unity version.
  3. You need to add references to game files 'Assembly-CSharp.dll', 'Assembly-CSharp-firstpass.dll', 'UnityEngine.dll', 'UnityEngine.UI.dll' which are located in 'Managed' folder and to UMM files 'UnityModManager.dll', '0Harmony.dll' which are located in 'Managed/UnityModManager' folder. If the unity version is 2017 or higher you need to add additional files 'UnityEngine.CoreModule.dll', 'UnityEngine.IMGUIModule.dll'. Now we can use the game and unity mod manager functions. Note: Unity Mod Manager should already be installed.

Information file

Create an information file 'Info.json' so that the mod manager can read it and determine which files need to load when starting the game. The file is written in json and must be placed in the 'Mods' folder and one more folder e.g. '\Steam\steamapps\common\YourGame\Mods\TestMod\Info.json'.

{
  "Id": "TestMod",
  "DisplayName": "Test Mod",
  "Author": "username",
  "Version": "1.0.0",
  "ManagerVersion": "1.0.0",
  "Requirements": ["SomeMod-1.0.0", "AnotherMod"],
  "AssemblyName": "TestMod.dll",
  "EntryMethod": "TestMod.Main.Load"
}

OR short variant

{
  "Id": "TestMod",
  "Version": "1.0.0",
  "EntryMethod": "TestMod.Main.Load"
}

Id - Unique string. It is desirable to match the folder name. (Required)
DisplayName - Name or Title. (Optional)
Author - (Optional)
Version - Need for dependent mods and to check for updates. (Required)
ManagerVersion - Minimum required version of the mod manager. (Recommended)
Requirements - Minimum required version of mods or just other required mod. (Optional)
AssemblyName - Filename we are creating. Default like 'Id' (e.g. TestMod.dll). (Optional)
EntryMethod - A function that will be called by the mod manager at load game. (Required)
HomePage - Web address. (Optional)
Repository - Web address to check for updates. (Optional)

Assembly file

The mod manager supports several variants of the Entry functions. Use only one. Let's call it Load. The name must be the same as in the EntryMethod.

using UnityEngine;
using UnityModManagerNet;

namespace TestMod
{
    static class Main
    {
        // Simply call.
        static void Load() 
        {
            // Something
        }

        // Transfer a variable with data about the mod.
        static void Load(UnityModManager.ModEntry modEntry) 
        {
            // Something
        }

        // Send a response to the mod manager about the launch status, success or not.
        static bool Load(UnityModManager.ModEntry modEntry)
        {
            // Something
            return true; // If false the mod will show an error.
        }
    }
}

You can add a function that will control on/off mode. This function is optional. If the function is missing, the mod may turn on, but it will turn off only after restarting the game.

using UnityEngine;
using UnityModManagerNet;

namespace TestMod
{
    static class Main
    {
        public static bool enabled;

        static bool Load(UnityModManager.ModEntry modEntry)
        {
            modEntry.OnToggle = OnToggle;
            return true;
        }

        // Called when the mod is turned to on/off.
        // With this function you control an operation of the mod and inform users whether it is enabled or not.
        static bool OnToggle(UnityModManager.ModEntry modEntry, bool value /* active or inactive */)
        {
            SomeAction();
            enabled = value;
            return true; // If true, the mod will switch the state. If not, the state will not change.
        }
    }
}

Details of ModEntry

Info - Contains all fields from the 'Info.json' file.
Path - The path to the mod folder e.g. '\Steam\steamapps\common\YourGame\Mods\TestMod\'.
Active - Active or inactive.
Logger - Writes logs to the 'Log.txt' file.
OnToggle - The presence of this function will let the mod manager know that the mod can be safely disabled during the game.
OnGUI - Called to draw UI.
OnSaveGUI - Called while saving.
OnUpdate - Called by MonoBehaviour.Update.
OnLateUpdate - Called by MonoBehaviour.LateUpdate.
OnFixedUpdate - Called by MonoBehaviour.FixedUpdate.

Examples

A simple example of how to bind any action to keys.

using UnityEngine;
using UnityModManagerNet;

namespace TestMod
{
    static class Main
    {
        public static bool enabled;

        static bool Load(UnityModManager.ModEntry modEntry)
        {
            modEntry.OnUpdate = OnUpdate;
            return true;
        }

        static void OnUpdate(UnityModManager.ModEntry modEntry, float dt)
        {
            if (Input.GetKeyDown(KeyCode.F1))
            {
                 Player.health = 9999f;
                 Player.weapon.ammo = 9999f;
            }
        }
    }
}

An example of how to draw a mod menu for a UMM UI. Some IMGUI documentation.

using UnityEngine;
using UnityModManagerNet;
using UnityEngine.UI;

namespace TestMod
{
    static class Main
    {
        public static bool enabled;
        public static string health;
        public static string ammo;

        static bool Load(UnityModManager.ModEntry modEntry)
        {
            modEntry.OnGUI = OnGUI;
            return true;
        }

        static void OnGUI(UnityModManager.ModEntry modEntry)
        {
            GUILayout.Label("God mode");
            health = GUILayout.TextField(health, GUILayout.Width(100f));
            ammo = GUILayout.TextField(ammo, GUILayout.Width(100f));
            if (GUILayout.Button("Apply") && int.TryParse(health, out var h) && int.TryParse(ammo, out var a))
            {
                 Player.health = h;
                 Player.weapon.ammo = a;
            }
        }
    }
}

Harmony

With harmony patches, you can completely take control of game functions. How to do this better to read the official Wiki. Here is an example.

using UnityEngine;
using Harmony;
using UnityModManagerNet;

namespace TestMod
{
    static class Main
    {
        public static bool enabled;

        static bool Load(UnityModManager.ModEntry modEntry)
        {
            modEntry.OnToggle = OnToggle;

            var harmony = HarmonyInstance.Create(modEntry.Info.Id);
            harmony.PatchAll(Assembly.GetExecutingAssembly());

            return true;
        }

        static bool OnToggle(UnityModManager.ModEntry modEntry, bool value) 
        {
            enabled = value;
            modEntry.Logger.Log(Application.loadedLevelName);

            return true;
        }
    }

    [HarmonyPatch(typeof(Application), "loadedLevelName", MethodType.Getter)]
    static class Application_loadedLevelName_Patch
    {
        static void Postfix(ref string __result)
        {
            if (!Main.enabled)
                return;

            __result = "New Level Name";
        }
    }
}

Now the function 'Application.loadedLevelName' will always return "New Level Name" string. Similarly, we can change any value in the game.

Finally

Last, compile this code and copy the 'TestMod.dll' file to the 'Info.json' file. After starting the game, you will see messages in the 'Log.txt' file. Also detailed log can be found in 'YourGame\YourGame_Data\output_log.txt' or 'c:\Users%USERNAME%\AppData\LocalLow\YourGame\output_log.txt'.

Additionally

You can explore the game code using the dnspy tool. Also available source code of my mods.