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Make your own door, switch or lever

This page shows how to build four things of your own. A door that a button or a lever opens. Any other actor that a button or a lever switches. An emitter, such as a pressure plate. And an object the player drags by hand, such as a drawer, a valve or a hatch. If you have not read How interaction works, start there.

  • Doors: Content/MPFriendslop/Blueprints/Environments/Doors/
  • Buttons and levers: Content/MPFriendslop/Blueprints/Environments/Fixtures/
  • The link and the axis: Content/MPFriendslop/Blueprints/ActorComponents/
  • The parent of hand-dragged objects, BP_GrabAxisBase: Content/MPFriendslop/Blueprints/Environments/
Start from Take this one when What it brings
BP_DoorBase A button or a lever opens it The open or closed state, the timing, the link
BPI_Activatable It is not a door, but a button or a lever switches it Two events to fill in
BP_ActivationLinkComponent You make your own emitter: a pressure plate, a zone, a timer A list of targets to switch
BP_GrabAxisBase The player drags it by hand along one axis Everything, with zero graph

A door of your own

BP_DoorBase already knows whether the door is open and how far along it is. Your child only decides how its meshes move. BP_SlidingDoor_Double slides two leaves, and BP_ExtractionTrap swings two leaves down by Open Angle: open either one to copy from.

  1. Right click BP_DoorBase, then Create Child Blueprint Class. Save it in Doors/Childs/.
  2. Add your meshes. Keep the fixed frame and the moving parts as separate components, and put the pivot of a swinging part on its hinge.
  3. Add the variable your movement needs, for example a travel in cm or an angle in degrees, in the category Settings|Door and Instance Editable.
  4. Override ApplyDoorAlpha. Its Alpha input goes from 0 (closed) to 1 (open), already eased. Lerp your part from its closed pose to its open pose with it, and set its relative location or rotation.
  5. Place it and link a button or a lever to it, as in Link a button or a lever to a door.

That is the whole job. You do not add a Timeline or a Tick: the base moves Alpha, and stops ticking once the door has arrived.

Field What it does Shipped default
Is Open The door state. Tick it on a placed door to start it open off
Move Duration Seconds for a full open or close. 0 is instant 0.8
Open Travel On BP_SlidingDoor_Double only: how far each leaf slides, in cm 114

For a sound or an effect when the door moves, bind OnDoorStateChanged on your child.

Dispatcher When it fires Fires on
OnDoorStateChanged Is Open changed. Gives Is Open every player

Let a button or a lever switch your own actor

A button or a lever does not know what it switches. It sends one of two messages from BPI_Activatable to every actor in its Targets:

Message Sent by What your actor does
Toggle BP_InteractButton Flips its state
SetActivated BP_LeverBase Takes the Activated value it receives
  1. Open your actor, then Class Settings, and add BPI_Activatable to Implemented Interfaces.
  2. Keep the state in a variable set to RepNotify, and apply the visual in its OnRep function.
  3. Implement Toggle and SetActivated: they only write that variable.
  4. In Class Defaults, tick Replicates.

The lamps are a good first case, because they do not implement BPI_Activatable when they ship. Make a child of BP_LightBase, add the interface, and in its two events call SetLightActive on its BP_LightComponent: Toggle passes the opposite of Is Light Active, SetActivated passes Activated. The component already keeps the state in a replicated variable, so the lamp needs no variable of its own. More on lamps in Place, switch and make lamps.

Your own emitter: a pressure plate or a zone

Anything can switch targets: add a BP_ActivationLinkComponent to it and call it. The template ships no pressure plate, so here is the recipe.

  1. Make an actor with a Box Collision and a BP_ActivationLinkComponent. Tick Replicates.
  2. On the box's On Component Begin Overlap, call SetTargetsActivated on the link with Activated true.
  3. On On Component End Overlap, call it with Activated false. If several players can stand on it, first check that nothing is left on the box.
  4. Place it, and pick its targets in Targets with the eyedropper.
On BP_ActivationLinkComponent What it does
Targets The actors it switches, picked in the level
ToggleTargets Sends Toggle to every target
SetTargetsActivated Sends SetActivated to every target

Both functions only act on the server. On a player's machine they do nothing. An overlap fires on every machine, so you can call them from it without checking authority yourself.

An object dragged by hand

A drawer, a valve or a hatch is a child of BP_GrabAxisBase with a BP_GrabAxisComponent. The player grabs it with the left mouse button and moves it along one axis. BP_SlidingDoor_Single is built this way, with no variable and no graph of its own.

  1. Right click BP_GrabAxisBase, then Create Child Blueprint Class.
  2. Add the fixed mesh.
  3. Add a BP_GrabAxisComponent under it, placed exactly on the hinge, or at the start of the rail.
  4. Attach the moving mesh under the BP_GrabAxisComponent. Leave it in its closed pose: Min Value and Max Value are measured from that pose.
  5. Fill Settings|Axis on the BP_GrabAxisComponent.
  6. Optional: add a BP_OutlineComponent and list your mesh names in its Mesh Names.
Field What it does Default Lever Single door
Axis Type Angular for a hinge, Linear for a rail Angular Angular Linear
Axis The axis it turns around or slides along, in its parent's space (0,0,1) (-1,0,0) (1,0,0)
Min Value Degrees or cm at the closed end 0 -45 0
Max Value Degrees or cm at the open end 90 115 115
Snap Positions 0 is free. 2 snaps to closed or open, 3 adds a middle notch 0 2 0
Snap Speed How fast it settles into the nearest notch after release 4 4 2
Drag Sensitivity How much it moves for a given gesture. Lower feels heavier 1 0.25 0.7
Follow Speed How closely it follows the hand. Lower lags more 8 6 5
Release Damping Without notches, how fast it slows down after you let go 4 0 4
Smoothing Speed How smoothly the pose is drawn on the other players' screens 12 12 12
Drive Speed When it moves by itself, for example a door that an enemy bumps, how many full strokes per second 1 1 1

To have enemies open it too, see Doors the Warden can open.

To react to the position, bind OnAxisAlphaChanged. GetAxisValue gives the current angle or distance.

Dispatcher When it fires Fires on
OnAxisAlphaChanged The position changed. Gives Alpha, from 0 to 1 every player

To make a handle that switches other things, duplicate BP_LeverBase and swap its meshes. It sends SetTargetsActivated when its Alpha crosses Activation Alpha (0.5).

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