Why does my burst stop emitting partway through?

A Spawn Context input wired to an exposed property may evaluate to 0 if the property changes mid-burst (e.g. Speed = 0 when player stops). Use Single Burst block for one-shot bursts so the rate isn't continuously evaluated.

Single Burst vs Constant Spawn Rate?

Single Burst: spawns N particles once. Constant Spawn Rate: continuously emits at the rate. For an explosion, Single Burst. For continuous fire, Constant.

Should I cache the rate in a property?

For varying rate driven by gameplay, yes. Pass via vfx.SetFloat from script and clamp to a sensible minimum. Don't let the property go below 1 if you expect particles.

Fix: Unity VFX Graph Spawn Rate Drops to Zero Mid-Burst

Quick answer: For one-shot bursts, use Single Burst block (spawn N at once, then done). Constant Spawn Rate continuously evaluates inputs and may go to zero if a property dips. Cache rate or use Single Burst.

VFX system spawns sparks correctly when player presses a button, then stops mid-burst because Speed went to 0 in the spawn rate expression.

The Symptom

Burst spawn produces fewer particles than expected, or stops abruptly. Re-triggering doesn’t restore expected count.

The Fix

Single Burst for one-shot.

Spawn Context:
  + Single Burst
      Count:           50
      Delay:           0

Single Burst fires count then stops. Doesn’t depend on continuous rate evaluation.

Continuous with cached rate.

Spawn Context:
  + Constant Spawn Rate
      Rate:  Property "_SpawnRate" (cached, not derived from Speed)

Set _SpawnRate from script with a stable value:

vfx.SetFloat("_SpawnRate", Mathf.Max(10f, currentRate));

Verifying

Trigger the effect. Count particles in the Niagara/VFX overlay. Single Burst always emits count; Constant runs at the rate as expected.

“Single Burst for explosions. Cached rate for continuous. No mid-burst dropout.”

Related Issues

For VFX Graph events, see events. For VFX Graph attribute mapping, see attribute mapping.

Single Burst owns count. Cached rate stays steady.