Play particles in editor without having the simulation selected.

PlayParticlesInEditorExtension.cs

/* LICENSE
Copyright (c) 2021 Adrian Babilinski
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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The above copyright notice and this permission notice shall be included in all
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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SOFTWARE.
*/
using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

namespace CommonTools.Extensions
{
	public static class ParticlesExtensions
	{
#if UNITY_EDITOR
		private static Dictionary<ParticleSystem, Unity.EditorCoroutines.Editor.EditorCoroutine> _simulationCoroutinesByParticleSystem;
		private static Dictionary<ParticleSystem, bool> _autoRandomSeedByParticleSystem;
#endif


		/// <summary>
		/// Plays the particle system inside the editor without having to select it. (if called during Play Mode, particle system will play as usual)
		/// </summary>
		/// <param name="particleSystem">this</param>
		/// <param name="withChildren">Play all children particles as well</param>
		/// <param name="effectFinishedEditorEvent">action call back when system is finished [Does Not Work Outside Of Unity Editor] </param>
		public static void PlayInEditor(this ParticleSystem particleSystem, bool withChildren, Action effectFinishedEditorEvent)
		{

			if (Application.isPlaying)
			{
				//play system as normal when game is playing
				particleSystem.Play(withChildren);
#if UNITY_EDITOR
				//wait for particleSystem.IsPlaying to equal false
				Unity.EditorCoroutines.Editor.EditorCoroutineUtility.StartCoroutine(DoCallbackWhenFinished(particleSystem), particleSystem);
#endif
				return;
			}
#if UNITY_EDITOR
			//When playing the system in the editor, we have to control each child individually
			var particleSystems = withChildren ? particleSystem.GetComponentsInChildren<ParticleSystem>(true) : new[]{particleSystem.GetComponentInChildren<ParticleSystem>(true)};
			
			var particleCount = particleSystems.Length;
			var finishedParticleCount = 0;

			if (_simulationCoroutinesByParticleSystem == null)
			{
				//Store a dictionary of systems so that we do not start multiple coroutines
				_simulationCoroutinesByParticleSystem = new Dictionary<ParticleSystem, Unity.EditorCoroutines.Editor.EditorCoroutine>();
			}

			if (_autoRandomSeedByParticleSystem == null)
			{
				//Store a dictionary of systems so that we can reset the random seed value after playing
				_autoRandomSeedByParticleSystem = new Dictionary<ParticleSystem, bool>();
			}

			foreach (var childParticleSystem in particleSystems)
			{
				if (!childParticleSystem.gameObject.activeInHierarchy)
				{
					continue;
				}

				if (_simulationCoroutinesByParticleSystem.TryGetValue(childParticleSystem, out Unity.EditorCoroutines.Editor.EditorCoroutine editorCoroutine))
				{
					//if the system is currently playing or the coroutine was interrupted previously, make sure to stop the system and remove the dictionary item
					childParticleSystem.Stop(false, ParticleSystemStopBehavior.StopEmittingAndClear);
					Unity.EditorCoroutines.Editor.EditorCoroutineUtility.StopCoroutine(editorCoroutine);
					_simulationCoroutinesByParticleSystem.Remove(childParticleSystem);

					if (_autoRandomSeedByParticleSystem.TryGetValue(childParticleSystem, out bool isOn))
					{
						//if the system is currently playing or the coroutine was interrupted previously, make sure to set the autoRandomSeed value to the original value
						childParticleSystem.useAutoRandomSeed = isOn;
						_autoRandomSeedByParticleSystem.Remove(childParticleSystem);
					}
				}

				
				var currentEditorCoroutine = Unity.EditorCoroutines.Editor.EditorCoroutineUtility.StartCoroutine(PlaySingleParticleSystemInEditor(childParticleSystem, () =>
																																										{
																																											finishedParticleCount++;
																																											// if we ar playing children, only do master call back once all systems finish
																																											if (finishedParticleCount == particleCount)
																																											{
																																												effectFinishedEditorEvent?.Invoke();
																																											}
																																										}), childParticleSystem);
				_simulationCoroutinesByParticleSystem.Add(childParticleSystem, currentEditorCoroutine);
			}


#endif

		}

		/* ---------------------------------------------------------------------------------------- */
		/* ------------------------ Shorthand Methods --------------------------------------------- */
		/* ---------------------------------------------------------------------------------------- */
		#region Shorthand
/// <summary>
/// Plays the particle system inside the editor without having to select it. (if called during Play Mode, particle system will play as usual)
/// </summary>
/// <param name="particleSystem">this</param>
/// <param name="withChildren">Play all children particles as well</param>
public static void PlayInEditor(this ParticleSystem particleSystem, bool withChildren)
		{
			particleSystem.PlayInEditor(withChildren, null);
		}

		/// <summary>
		/// Plays the particle system and it's children inside the editor without having to select it. (if called during Play Mode, particle system will play as usual)
		/// </summary>
		/// <param name="particleSystem">this</param>
		public static void PlayInEditor(this ParticleSystem particleSystem)
		{
			particleSystem.PlayInEditor(true, null);
		}

		/// <summary>
		/// Plays the particle system and it's children inside the editor without having to select it. (if called during Play Mode, particle system will play as usual)
		/// </summary>
		/// <param name="particleSystem">this</param>
		/// <param name="effectFinishedEditorEvent">action call back when system is finished [Does Not Work Outside Of Unity Editor] </param>
		public static void PlayInEditor(this ParticleSystem particleSystem, Action effectFinishedEditorEvent)
		{
			particleSystem.PlayInEditor(true, effectFinishedEditorEvent);
		}
		#endregion

		/* ---------------------------------------------------------------------------------------- */
		/* --------------------------------- Worker Coroutines ------------------------------------ */
		/* ---------------------------------------------------------------------------------------- */
		#region Editor Coroutines
		static IEnumerator DoCallbackWhenFinished(ParticleSystem particleSystem, Action effectFinished = null)
		{
			//[always check if the state of the system changes or if we exit play mode]
			
			
			float curTime = 0;
			while (curTime<particleSystem.time && particleSystem != null&& particleSystem.isPlaying)
			{
				curTime = particleSystem.time;

				yield return null;
			}

			if (particleSystem != null &&  particleSystem.isPlaying)
			{
				effectFinished?.Invoke();
			}
		}
		static IEnumerator PlaySingleParticleSystemInEditor(ParticleSystem particleSystem, Action effectFinished=null)
		{
			
			bool isAutoRandomSeed = particleSystem.useAutoRandomSeed;
			_autoRandomSeedByParticleSystem.Add(particleSystem, isAutoRandomSeed);
			particleSystem.Stop(false,ParticleSystemStopBehavior.StopEmittingAndClear);
			
			yield return null;
			var mainSystem = particleSystem.main;
			var totalTime = mainSystem.startLifetimeMultiplier * mainSystem.duration;
			particleSystem.randomSeed = (uint) UnityEngine.Random.Range(0, int.MaxValue);
			var curTime = 0.0f;

			yield return null;
			//update system to play state
			particleSystem.Play(false);
			//Time.deltaTime does not work in editor so we use the Unity Time Since Startup
			var initialTime = (float) UnityEditor.EditorApplication.timeSinceStartup;

			while (curTime < totalTime && particleSystem != null && particleSystem.gameObject.activeInHierarchy)
			{

				// in order to play in edit mode, both Simulate and time have to be changed. 
				particleSystem.Simulate(curTime, false, true);
				particleSystem.time = curTime;
				//track delta between start and current Unity Time Since Startup
				curTime = (float) UnityEditor.EditorApplication.timeSinceStartup- initialTime;


				yield return null;
			}

			if (particleSystem != null)
			{
				//update system to stop state
				particleSystem.Stop(false, ParticleSystemStopBehavior.StopEmittingAndClear);

				yield return null;

				if (isAutoRandomSeed)
				{
					//restore random seed value back to original value
					particleSystem.randomSeed = 0;
					particleSystem.useAutoRandomSeed = isAutoRandomSeed;
				}
				//remove item from dictionary when system finishes
				_autoRandomSeedByParticleSystem.Remove(particleSystem);
				_simulationCoroutinesByParticleSystem.Remove(particleSystem);
				yield return null;

				effectFinished?.Invoke();


			}
			
		}

		#endregion

	}
}

Adds the ability to play particles in editor without having to have the simulation selected.

Adds:

• CommonTools.Extensions.PlayInEditor() - Plays the particle system inside the editor without having to select it. (if called during Play Mode, particle system will play as usual)

Params:

• WithChildren - Play all children particles as well
• EffectFinishedEditorEvent - action call back when system is finished [Does Not Work Outside Of Unity Editor]