Wikis / Unreal Wiki / Legacy:Mod Authoring/The Anatomy Of Mutator

So now you've had your first exposure to writing a simple UT mod. Clearly this isn't enough to shake the world or get a job in the industry. Let's take a close look at the methods inside the Mutator base class. This will give you a better idea of what you can do with them. It only scratches the surface, however, because you have the power to use a multitude of inherited functions as well as interact with other objects.

ModifyPlayer 

We'll skip the PostRender function for now and look at ModifyPlayer. This is called by the game whenever a Pawn (UT) is respawned. It gives you a chance to modify the pawn's variables or perform some game logic on the pawn. Remember to call Super.ModifyPlayer() if you override this function. That will call the parent class' version of the function.

ScoreKill 

is called whenever a pawn kills another pawn. This lets you influence the score rules of the game, preventing point gains in certain situations or awarding more points in others. Remember to call Super.ScoreKill() if you override this function.

MutatedDefaultWeapon 

gives you an opportunity to give a different default weapon to a player that enters a game or respawns. In UT, the default weapon is the Enforcer. If you just want to change the default weapon, you don't need to override this function. Instead, just add a DefaultWeapon definition to the defaultproperties of your mutator. (See the bottom of PulseArena for an example).

MyDefaultWeapon, AddMutator 

You don't need to mess with MyDefaultWeapon or AddMutator.

ReplaceWith, AlwaysKeep 

allow you to interdict objects that the game wants to add to the world. You can replace objects on the fly with other objects as they appear. The Botpack.Arena mutators are a great example of this. They take all the weapons in a game and replace them with one other weapon. If you are adding a new weapon to the game, you might want to add an Arena mutator for it.

IsRelevant 

is called when the game wants to add an object to the world. You can override it with special code and return true, to keep the object, or false, to reject it. If you say false, the object will be destroyed.

Mutate 

is cool. It lets your mutator define new commands that player's can bind to keys. If a player binds "mutate givehealth" to a key and then uses that key, every mutator will get a mutate call with a "givehealth" parameter. Your mutator might look for this string and give the player who sent the message some extra health.

MutatorTakeDamage 

as described above, is called on DamageMutators. It lets damage mutators do some kind of game logic based on a pawn taking damage. It also tells you where the pawn was hit, the type of damage, and how much force the damage imparted.

RegisterHUDMutator 

is used to tell the game that this mutator should get PostRender calls. PostRender passes you a Canvas every frame. You can use the Canvas to draw stuff on the HUD. Look in the Botpack.ChallengeHUD class for extensive examples of abusing the Canvas. Hehe.

The best way to learn mutators is to read the code in the mutators that ship with UT. In fact, you'll probably want to spend a lot of time just pooring over the massive amount of code that comes with the game. Trace execution paths and look at how the various classes override and interact with each other. It can be very intimidating at first, but with time you'll get more experienced with where things are and what things do. Don't be afraid to go online and ask questions either or read other mod authors code. If you spend the time it takes to learn, you will be rewarded with the ability to take on larger, more difficult projects.

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