Why does my GetActiveParticleCount return 0?

You're querying before the system ticks, or asking the wrong API. Use GetSystemInstanceController()->GetSimulationForHandle and GetParticleCount per emitter, called after the tick (LateTick or PostUpdate).

GPU emitters add a wrinkle?

GPU particle counts come back via async readback with 1-3 frame latency. Don't expect frame-exact counts for GPU. CPU emitters are immediate.

Should I use a User Parameter for cross-emitter awareness?

For decisions inside Niagara, yes — expose a User float, set from script, read in Particle Update. Simpler than querying counts back to script every frame.

Fix: Unreal Niagara System Active Particle Count Not Updating

Quick answer: Query particle count via the SystemInstanceController per emitter, after the tick. CPU emitters return live counts; GPU emitters lag by a few frames due to async readback.

You want to gate gameplay on “all spawned particles done.” GetActiveParticleCount returns 0 even though particles visibly exist.

The Symptom

API call from C++ returns wrong count. Visual count obvious in the Niagara overlay debugger.

The Fix

UNiagaraComponent* Comp = ...;
TSharedPtr<FNiagaraSystemInstanceController> Ctrl = Comp->GetSystemInstanceController();
if (Ctrl.IsValid())
{
    int32 Total = 0;
    for (int32 i = 0; i < Comp->GetAsset()->GetEmitterHandles().Num(); ++i)
    {
        FNiagaraEmitterInstance* Em = Ctrl->GetSimulationForHandle(i).Get();
        if (Em) Total += Em->GetParticleCount();
    }
    UE_LOG(LogTemp, Log, TEXT("Active: %d"), Total);
}

Loop through emitters, sum counts. Call from PostUpdate or after manual Tick to ensure data is fresh.

GPU Emitters

GPU counts use async readback. Expect 1–3 frames of latency. For gating on “completely done,” wait until count is 0 for several consecutive frames.

Verifying

Spawn a known number of particles via Burst Spawn = N. Wait one tick. Query count; should return N. Subsequent frames decrease as particles expire.

“Per-emitter count after tick. GPU has lag. Sum gives total.”

Related Issues

For Niagara CPU/GPU readback, see CPU/GPU readback. For Niagara mesh attribute, see mesh attribute.

Per-emitter, after tick. Counts arrive.