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How weapons work

The template has two kinds of weapon. A gun is an inventory item with a BP_WeaponComponent on its held actor. A melee weapon is a grabbed object with a BP_MeleeComponent on it. Both are tuned by a Data Asset, and both deal Unreal's own damage, so anything that listens to engine damage can be hurt by either.

  • The components: Content/MPFriendslop/Blueprints/ActorComponents/
  • The gun Data Assets: Blueprints/DataAssets/Weapon/Childs/
  • The melee Data Assets: Blueprints/DataAssets/Melee/Childs/

This page is the mental model. The pages after it are the recipes.

What one gun is made of

A gun is three assets that point at each other:

Asset What it is The shipped one
The item A DA_Item_* like any other item. Its Max Charge is the clip size DA_Item_Shotgun_SawedOff, Max Charge 2
The held actor A child of BP_WieldedItem, named in the item's Wield Actor Class. It carries the BP_WeaponComponent BP_WieldedShotgun
The weapon data A DA_Weapon_*, set in the component's Weapon Data DA_Weapon_Shotgun_SawedOff

One gun ships, the sawed-off shotgun. Items in general are on How items and the inventory work.

The Data Asset is a child of BP_WeaponDataAsset. Its fields sit in five categories under Settings:

Category Fields Shotgun
Fire Fire Mode, Rounds Per Minute, Burst Count, Pellets Per Shot, Spread Degrees, Range, Damage Per Pellet, Ammo Per Shot, and three fire montages: Fire Montage FPS, Fire Montage TPS, Fire Montage World Single, 200 rpm, 8 pellets of 9 damage, 5 degrees, 3000 cm
Reload Reload Seconds and three reload montages: Reload Montage FPS, Reload Montage TPS, Reload Montage World 3.2 s
Recoil Recoil Pitch, Recoil Yaw, Recoil Recovery Speed, Camera Shake 4, 1.2, 6, CS_WeaponFire
Effects Muzzle Socket Name, Muzzle FX, Impact FX Muzzle, NS_Shotgun_Fire, NS_Weapon_Impact
Audio Fire Sound, Dry Fire Sound, Impact Sound CUE_ShotgunFire, CUE_DryFire, CUE_Impact_Metal

Fire Mode comes from E_FireMode: Single, Burst or Auto. The shotgun uses Single. Burst and Auto are built into the component, but no shipped gun uses them.

Firing, ammo and reload

  • Fire. Right Mouse uses the selected item, and for a gun a use is a shot. Each pellet is a line trace on the Weapon trace channel, spread inside a cone of Spread Degrees, and deals Damage Per Pellet.
  • Ammo. The ammo is the item's charge. Each shot removes Ammo Per Shot from the slot. The HUD slot draws it as the charge strip. At zero, the gun plays Dry Fire Sound for the shooter only.
  • Reload. R refills the slot to Max Charge after Reload Seconds. It does nothing when the gun is already full. The reserve is infinite: there is no ammo item to find.
  • Recoil. Recoil kicks your aim up by Recoil Pitch and sideways by a random amount up to Recoil Yaw, then comes back at Recoil Recovery Speed.

The charge belongs to the slot. Drop the shotgun with one shell left, and whoever picks it up has one shell.

Each shot plays three montages: Fire Montage FPS on the weapon you see in your hands, Fire Montage TPS on your body for the other players, and Fire Montage World on the weapon they see. The reload does the same with Reload Montage FPS, Reload Montage TPS and Reload Montage World. When the gun is put away or dropped in the middle of one, the two weapon montages end with the weapon, and BP_WeaponComponent stops its TPS montages on the body, on every machine. An emote playing at the same time is left alone. A new gun is covered step by step on Add a new gun.

What one melee weapon is made of

Any grabbed object can hit. The baseball bat and the hammer are loot, BP_Loot_BaseballBat and BP_Loot_Hammer, each with a BP_MeleeComponent whose Melee Data points at DA_Melee_BaseballBat or DA_Melee_Hammer. There is no key for a hit: you grab the object with Left Mouse and swing the mouse.

  • A swing. Your view has to turn fast, at least Swing Turn Speed degrees per second over Swing Turn Window seconds. The swing then stays open for Swing Duration seconds. Walking or running with the object does not strike.
  • The strike zone. The segment between two mesh sockets, Strike Start Socket and Strike End Socket, swept with spheres of Strike Radius. It hits only the object types in Strike Object Types: Pawn and PhysicsBody on the shipped weapons.
  • The damage. The faster the tip moves, the harder it hits: from Min Damage at Min Strike Speed to Max Damage at Max Strike Speed. Below Min Strike Speed nothing happens. Knockback pushes the victim.

The fields are in Settings|Swing, Settings|Strike, Settings|Damage, Settings|Audio and Settings|Effects of BP_MeleeDataAsset. The full table and the recipe are on Turn any grabbable object into a melee weapon.

Two limits worth knowing: an inventory item in your hand, the shotgun included, cannot be swung as a melee weapon. And a victim takes the damage and the push, with no hit reaction animation.

Make your actor take damage

A gun and a melee weapon both call Unreal's Apply Point Damage on the server. So your actor takes damage when two things are true:

  1. It can be hit. For a gun, its collision must block the Weapon trace channel. The channel blocks by default. So this only fails when you set your actor's collision to ignore it. For a melee weapon, its object type must be in the Data Asset's Strike Object Types.
  2. It listens to engine damage. Add BP_VitalsSystem, like the player and the Warden. Or bind On Take Any Damage on your actor and handle the amount yourself, on the server.

With BP_VitalsSystem, the actor loses health, flashes with the Impact Flash Material, and at 0 health the component calls OnDeath from BPI_VitalManagerInterface on its owner. The Warden implements it and disappears. That event is where a ragdoll or a drop of your own goes. The component's fields are on Health, damage and new vitals.

Warning

Nothing tells you that a trace went through your actor. If a gun never hurts it, check its collision against the Weapon channel first, not your damage code.

Where to go next

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