How interaction works¶

Anything the player looks at and uses with E goes through one interface and one component. The interface, BPI_Interactable, goes on the thing you use. The component, BP_InteractionComponent, goes on the player.

The interfaces: Content/MPFriendslop/Blueprints/Interfaces/
The components: Content/MPFriendslop/Blueprints/ActorComponents/

The player character never knows what it is looking at. The object answers for itself: its prompt, how it is used, and what happens. So a new kind of interactable never needs an edit on the player.

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

The interface on the object¶

BPI_Interactable has five functions. An actor that implements it can be used. It also needs the two settings listed after the component table.

Function	What the object does in it
`GetInteractionData`	Returns `Prompt` (the line under the ring), `Type` and `Duration`
`CanInteract`	Returns true when the player passed as `Interactor` may use it right now
`Interact`	Does the actual work. Runs on the server
`StartFocus`	The player started looking at it. For a cosmetic highlight only
`EndFocus`	The player stopped looking at it

Type is an E_InteractionType, with three entries:

Type	How the player uses it
`Simple`	One press
`Hold`	Hold the key until the ring fills. `Duration` is the time in seconds. Looking away or stepping out of range cancels it. The player then presses again
`Spam`	Each press adds `Spam Press Gain` to the ring, and it drains on its own between presses. It completes when the total reaches `Duration`. If it drains to empty, the attempt is canceled

There is no Enhanced Input trigger and no timer to add for Hold or Spam. The one IA_Interact action serves all three types, and the object only returns its type and its Duration.

The template ships three interactables you can open as examples: BP_InteractButton (a button that switches a door), BP_ItemPickup (an item lying in the world) and BP_ReviveBay.

The component on the player¶

BP_InteractionComponent sits on BP_FriendslopCharacter. Every Trace Interval it traces from the player's eyes, asks the actor it hits CanInteract, and hands the prompt to the HUD. WBP_Interact, the ring and text at the centre of the screen, finds the component by itself.

Its fields are in Settings|Interaction:

Field	What it does	Shipped default
`Trace Distance`	How far the player reaches, in cm	`250`
`Trace Interval`	Seconds between two traces	`0.1`
`Trace Channel`	The channel the trace uses	`Visibility`
`Spam Press Gain`	How much one press adds on a `Spam` object. The ring is full when the total reaches the object's `Duration`	`0.15`
`Spam Decay Rate`	How much drains per second on a `Spam` object, in the same unit	`0.4`
`Server Distance Tolerance`	The server accepts a use from up to `Trace Distance` times this value	`1.5`

Two settings on the object itself decide whether it can be used at all:

It must block the Trace Channel (Visibility by default). Otherwise it is never looked at and never shows a prompt.
It must have Replicates ticked, even if it has nothing to replicate. The server has to recognise the actor the player sends it.

Who decides¶

The looking is local. Each player traces, draws the ring and fills it on their own machine. When the ring completes, the component asks the server once. The server checks the distance and CanInteract again, and only then calls Interact on the object.

So what Interact changes must be state the object keeps in a Replicated variable. That way every player sees the result, including a player who joins late.

The dispatchers¶

Bind these to build your own prompt, sounds or tutorial without opening the component.

Dispatcher	When it fires	Fires on
`OnFocusChanged`	The aimed object changed. Gives `Focused Actor`, `Prompt`, `Type` and `Duration`. An empty actor means nothing is aimed	owning player
`OnInteractionStarted`	The press began on a target	owning player
`OnInteractionCompleted`	The ring completed, before the server has answered	owning player
`OnInteractionCanceled`	A `Hold` or `Spam` was abandoned	owning player

Warning

Never give a reward from OnInteractionCompleted. It fires on the player's machine before the server has checked anything, and the server may still refuse. The reward goes in the object's Interact.

Buttons, levers and what they switch¶

A button does not open a door by itself. A second interface, BPI_Activatable, is for things a machine switches rather than a player uses. It has two functions: Toggle and SetActivated.

The link between the two is BP_ActivationLinkComponent. It goes on the emitter and holds Targets, a list of actors you pick in the level with the eyedropper. When the emitter fires, every target that implements BPI_Activatable gets the message. A target that does not implement it simply does nothing.

BP_InteractButton calls ToggleTargets from its Interact.
BP_LeverBase is dragged by hand, and calls SetTargetsActivated when it passes its Activation Alpha.
BP_DoorBase implements BPI_Activatable and opens or closes.

The link only acts on the server. Called on a player's machine, it does nothing.

Levers and hand-dragged doors are grabbed, not used with E. That side is in How grabbing works.

Where to go next¶

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