I need two particle systems to behave identically to each other – Unity

Symptoms

When I create two or more particle systems, they behave differently to each other even when I have the same properties set.

Cause

This only occurs when random ranges are used in a particle system. The random ranges are created by a Particle random seed.

Resolution

You can solve this by creating a script (or using the example script below) to set the Random Seed manually via ParticleSystem.randomSeed. This will ensure that any random ranges will match up to each other.

In this GIF, the particles that look like shadows are a duplicate of the particles in the air, but both use the same seed.

You can use this script to set the Random Seed on the particle systems assigned to setSeedParticles.

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class SetParticleSeed : MonoBehaviour {

    public ParticleSystem[] setSeedParticles;
    public int ParticleSeed;
    public bool forceNewSeed;

    void Start () {
        if (setSeedParticles.Length > 0) {
            for(int i = 0; i < setSeedParticles.Length; i++) {
                setSeedParticles[i].randomSeed = (uint) ParticleSeed;
            }
        }  
    }

     void Update () {
        if (forceNewSeed) {
            ParticleSeed = Random.Range(0,int.MaxValue);
            Debug.Log("Particle seed: " + ParticleSeed);

            if (setSeedParticles.Length > 0) {
                for(int i = 0; i < setSeedParticles.Length; i++) {
                    setSeedParticles[i].randomSeed = (uint) ParticleSeed;
                }
            }

             forceNewSeed = false;
        }
    }
}

More Information

Random Particle Seed - http://docs.unity3d.com/ScriptReference/ParticleSystem-randomSeed.html

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