Skip to content

Once

Lets exactly one pulse through until it is re-armed — a checkpoint, a pickup, a first-time event.

Output: event (one pulse, at the moment of the first trigger)

Inputs

Handle Type Meaning
trigger event the first pulse here passes; every later one is ignored
rearm event lets the next trigger through again

Parameters

Parameter Default Options
reset each round off re-arm by itself at the start of every round — see below
pulse 0.3 how long the output pulse lasts, in seconds (in the ⓘ Params tab, not on the card)

How it behaves

  • The first trigger is remembered and comes out as one pulse. Every trigger after that — from anyone — is ignored while the Once is spent.
  • Rearm forgets that first trigger: the Once is ready again and the next trigger passes.
  • All players work this out from the same shared trigger, so they agree on which press was first with nothing extra sent. A player who joins later is told the Once is already spent, so a door opened before they arrived stays open for them and does not fire again.

Reset each round

With reset each round on, a Once spent in an earlier round counts as armed again when a new round starts — a collectible counts once per round. Between rounds (game menu, round over) a round-scoped Once lets nothing through, and a press there does not re-arm it.

It only takes effect once the scene's game has been started at least once (see Build a game); in a scene without a game it behaves as if the option were off.

Practical example

A treasure chest that pays out only once:

  1. Add an On Click and an Object Selector picking the chest; wire On Click → Object Selector.
  2. Add a Once; wire On Click → Once's trigger.
  3. Add a Counter; wire Once → Counter's pulse.
  4. Add a Key Press (capture R); wire it → Once's rearm.
  5. Press Play and click the chest a few times: the Counter reads 1. Press R and the next click counts again.

On Click on the chest feeding a Once that counts into a Counter, with a Key Press wired to the Once's rearm

Tip

Once is the opposite of a Latch: a Latch holds a value, a Once passes a single pulse. For a pickup that should both count once and disappear, wire the same pulse into a Once (for the score) and a Latch (for the visibility).