C++ Mutator Tutorial - Epic Wiki

C++ Mutator Tutorial

Contents

• 1 C++ Mutator Tutorial
  • 1.1 Requirements
  • 1.2 Directory Structure
  • 1.3 UPlugin File
  • 1.4 Build.cs File
  • 1.5 Header File
  • 1.6 Plugin Module Interface
  • 1.7 The Mutator
  • 1.8 Building your Mutator
  • 1.9 Testing your Mutator

C++ Mutator Tutorial

This tutorial will teach you how to make a simple mutator for UT using C++. We'll be making a UE4 plugin that defines a child class of AUTMutator.

Requirements

• Engine version: 4.3
• Skill level: intermediate C++ knowledge

Directory Structure

• If UnrealTournament\Plugins does not already exist, create it
• Create a directory inside of UnrealTournament\Plugins to hold our mutator, in this case it would be "SampleMutator"
• Create a "Source" directory inside of the SampleMutator directory
• Create a "SampleMutator" directory inside of the "Source" directory
• Finally create a "Public" directory and a "Private" directory inside of the last "SampleMutator" directory that we made

UPlugin File

• We need to create SampleMutator.uplugin to let UE4 know we have a plugin it should load.
• On Windows, one way to do this is to create a new text file and rename the file extension to .uplugin. Copying an existing .uplugin file and editing it may not work!
• It should live at the same level that the Source directory does

SampleMutator.uplugin - Plugin defintion

{ "FileVersion" : 3,   "FriendlyName" : "Sample Mutator", "Version" : 1, "VersionName" : "1.0", "CreatedBy" : "Epic Games, Inc.", "CreatedByURL" : "http://epicgames.com", "EngineVersion" : "4.3.0", "Description" : "Sample Mutator", "Category" : "UnrealTournament.Mutator", "EnabledByDefault" : false,   "Modules" : [ { "Name" : "SampleMutator", "Type" : "Runtime", "WhitelistPlatforms" : [ "Win32", "Win64" ] } ] }

Build.cs File

• We need to create SampleMutator.Build.cs so that Unreal Build tool knows how to generate our dll file
• It should live at the same level that the Public and Private directories do
• We'll use the PrivateIncludesPaths array to make #include cleaner throughout our source files

SampleMutator.Build.cs - Unreal Build Tool definitions

namespace UnrealBuildTool.Rules { public class SampleMutator : ModuleRules { public SampleMutator(TargetInfo Target) { PrivateIncludePaths.Add("SampleMutator/Private");   PublicDependencyModuleNames.AddRange( new string[] { "Core", "CoreUObject", "Engine", "UnrealTournament", } ); } } }

Header File

• Unreal Build Tool requires that we have a shared header file as the first include in every cpp source file in the plugin.
• We'll put the SampleMutator.h header file inside of the Private directory
• We need to #include Core.h, Engine.h and UTMutator.h to have enough defintions to make a child class from AUTMutator
  1. include "SampleMutator.generated.h" is required by Unreal Header Tool
• We're only overriding CheckRelevance_Implemenation in this example, but more powerful mutators will overload more of the functions exposed by AUTMutator

SampleMutator.h - Sample Mutator class definition

#pragma once   #include "Core.h" #include "Engine.h" #include "UTMutator.h" #include "UTWeapon.h"   #include "SampleMutator.generated.h"   UCLASS(Blueprintable, Meta = (ChildCanTick)) class ASampleMutator : public AUTMutator { GENERATED_UCLASS_BODY()   bool CheckRelevance_Implementation(AActor* Other) OVERRIDE;     UPROPERTY() TSubclassOf<AUTWeapon> RocketLauncherClass; };

Plugin Module Interface

• Create SampleMutatorPlugin.cpp inside of the Public directory
• There's not much interesting in this file, it just provides UE4 a way to load this mutator as a plugin so I'm going to gloss over this file
• Note that SampleMutator.h must be the first #include and the IMPLEMENT_MODULE macro does all the heavy lifting

SampleMutatorPlugin.cpp - Plugin Module Interface

#include "SampleMutator.h"   #include "Core.h" #include "Engine.h" #include "ModuleManager.h" #include "ModuleInterface.h"   class FSampleMutatorPlugin : public IModuleInterface { /** IModuleInterface implementation */ virtual void StartupModule() override; virtual void ShutdownModule() override; };   IMPLEMENT_MODULE( FSampleMutatorPlugin, SampleMutator )   void FSampleMutatorPlugin::StartupModule() {   }     void FSampleMutatorPlugin::ShutdownModule() {   }

The Mutator

• This sample is going to replace all weapon pickups with Rocket Launcher pickups
  • We'll accomplish that by overriding the CheckRelevance_Implementation function and watching for AUTPickupWeapon
  • When we find a AUTPickupWeapon, we'll replace its WeaponType reference with a reference to BP_RocketLauncher_C
• Our mutator is going to live in SampleMutator.cpp inside the Public directory
• Note that once again SampleMutator.h has to be the first #include
• Our constructor is blank, but feel free to put initialization code in there in a future plugin
• StaticLoadClass is used to get the reference to Blueprint'/Game/RestrictedAssets/Weapons/RocketLauncher/BP_RocketLauncher.BP_RocketLauncher_C'
  • The use of a hardcoded reference here is very brittle and not considered good design, a mutator that requires direct blueprint references might be more easily implemented in blueprints
• Calling Super::CheckRelevance_Implementation(Other) is highly recommended as failing to do so won't call other mutators in the mutator list

SampleMutator.cpp - Replace all weapon pickups with rocket launcher pickups

#include "SampleMutator.h"   #include "UTPickupWeapon.h"   ASampleMutator::ASampleMutator(const FPostConstructInitializeProperties& PCIP) : Super(PCIP) { }   bool ASampleMutator::CheckRelevance_Implementation(AActor* Other) { // Find the rocket launcher blueprint if (RocketLauncherClass == nullptr) { RocketLauncherClass = StaticLoadClass(AUTWeapon::StaticClass(), nullptr, TEXT("Blueprint'/Game/RestrictedAssets/Weapons/RocketLauncher/BP_RocketLauncher.BP_RocketLauncher_C'")); }   // If a weapon pickup has a current weapon type, replace it with the rocket launcher AUTPickupWeapon *PickupWeapon = Cast<AUTPickupWeapon>(Other); if (PickupWeapon) { if (PickupWeapon->WeaponType != nullptr) { PickupWeapon->WeaponType = RocketLauncherClass; } }   return Super::CheckRelevance_Implementation(Other); }

Building your Mutator

• Right click your UnrealTournament.uproject in Window Explorer and select "Generate Visual Studio project files"
• Open up the Unreal Tournament solution file in Visual Studio
• Build the Unreal Tournament project in Development Editor configuration
• You will notice that in addition to UE4Editor-UnrealTournament.dll, UnrealTournament\Plugins\SampleMutator\Binaries\Win64\UE4Editor-SampleMutator.dll was generated

Testing your Mutator

• Run from a commandline "UE4Editor.exe UnrealTournament -game Example_Map?mutator=SampleMutator.SampleMutator"
• You should notice that the weapon pickups in the map have been replaced by Rocket Launchers

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Categories:

• Unreal Tournament
• UT Content Creation