Skip to content

Make any actor grabbable

By the end of this page, players can pick up your actor with the left mouse button, carry it with physics and drop it again, the same way they carry loot. You need one physics mesh, a few settings, and the BPI_Grabbable interface. You do not need to change the player.

If you have not read How grabbing works, and tuning the weight, start there.

  • The interface: Content/MPFriendslop/Blueprints/Interfaces/BPI_Grabbable
  • The ready-made loot: Blueprints/Environments/Loot/BP_LootBase and its children in Blueprints/Environments/Loot/Childs/

The quick way: a child of the loot base

If your object is loot, do not build it from scratch. Duplicate the BP_Loot_* child closest to yours, or make a new child of BP_LootBase.

  1. Set the Static Mesh on Mesh.
  2. On Mesh, in the Physics section, type the weight in Mass (kg). The override is already ticked on BP_LootBase.
  3. Fill Loot Data on its BP_LootValueComponent.

BP_LootBase already implements BPI_Grabbable and has every setting from the next section. A child sets only its mesh, its mass and its loot data. The loot side is covered in Add a loot item.

Your own actor

Use this when the object is not loot: a prop, a key part, a body. BP_PlayerHead in Blueprints/PlayerCharacter/ is the example that ships: it is grabbable without being a child of BP_LootBase.

  1. Make a Blueprint with parent Actor. Put your Static Mesh component at the root.
  2. On the mesh, tick Simulate Physics.
  3. In the Physics section, tick the override next to Mass (kg) and set the weight.
  4. In Collision, set a Custom profile with Collision Enabled on Query and Physics, object type PhysicsBody, Visibility on Block and Pawn on Ignore.
  5. Still in Collision, set Can Character Step Up On to No and tick Use CCD.
  6. In the actor's Class Defaults, under Replication, tick Replicates and Replicate Movement, and set Physics Replication Mode to Predictive Interpolation.
  7. In Class Settings, add BPI_Grabbable to Implemented Interfaces.
  8. Add a variable Current Holder of type Actor, set to Replicated.
  9. Fill in the interface functions from the table below.

That copies the collision of BP_LootBase. Pawn on Ignore is what lets players walk through the object instead of kicking it or standing on it.

The interface functions

Function What to return or do If you leave it empty
CanGrab true when nobody holds the object, or when Grabber is already the holder. BP_PlayerHead also refuses once the head sits in a revive bay. Returns false: nobody can ever grab it.
GetGrabMode Free, for a physics carry. Returns Free, which is what you want.
Grab Set Current Holder to Grabber. Nothing remembers who holds it.
Release If Current Holder is Grabber, clear it. The holder never clears.
GetGrabHolder Return Current Holder. Returns nothing. A melee weapon never finds who swings it, so it deals no damage.
GetGrabUpright Align Upright true, an Upright Offset and a Max Lean Angle, when the object must stay upright in the hand. BP_LootBase returns its own three fields of the same names. The object keeps the angle it had when you grabbed it.
GetGrabMotionComponent Nothing. The mesh you grabbed is used.

UpdateGrabAim is only for the Axis mode of levers and drawers, covered in Make your own door, switch or lever.

The settings that break it

Setting Where If it is wrong
Simulate Physics the mesh The server refuses the grab.
Visibility on Block the mesh collision The player's trace never sees the object: no open hand, no grab.
Replicates the actor What the server does to the object never reaches the clients.
Physics Replication Mode the actor Clients see the object stutter.
CanGrab the interface Left empty, it answers false.

Warning

Physics Replication Mode is not set for you by the grab component. BP_LootBase and BP_PlayerHead set it to Predictive Interpolation. Your own actor keeps the engine default until you change it, and nothing in the log tells you.

To turn your new grabbable into a weapon, see Turn any grabbable object into a melee weapon.

Join the Discord