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Question by s-joy-laube · Nov 09, 2020 at 03:37 PM · particlesparticlesystememit

'Swap' a particle from one system to another, keeping it's position

Hello, i am new to particles, so if there is a better way to do this, please point it out. I want a player to attract some particles and have them orbit around him. For this i have created an empty orbitParticleSystem around the player. The position of particles that go within a certain range of the player is saved and applied to a newly emitted particle in the orbitSystem with EmitParams.position. Now I have two problems:

  1. with ParticleSystem.EmitParams.applyShapeToPosition = false, the position is applied perfectly, but ofcourse the new orbit shape isn't applied. With ParticleSystem.EmitParams.applyShapeToPosition = true, the shape is applied properly but it just spawns somewhere on the orbit, not in the given position. I have a video to illustrate this: https://youtu.be/BV7NT8-Xsxs

  2. the old particle is not destroyed, even though it's lifetime is set to -1. By default the particles in that system have an infinite lifetime, but i thought it can be overwritten.

Here is my code:

 using System;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class ParticleAttractor : MonoBehaviour
 {
     public ParticleSystem[] pSystems;
     public float speedFactor = 2f;
     public float orbitStrength = 1f;
     private ParticleSystem.Particle[] particles;
     private int numParticlesAlive;
     public ParticleSystem orbitPSystem;
     private ParticleSystem.Particle particle;
 
     private void Start()
     {
         if (pSystems == null || pSystems.Length == 0)
         {
             Debug.LogError("No particle System assigned");
         }
     }

     void FixedUpdate()
     {    
             foreach (ParticleSystem pSystem in pSystems)
             {
                 //update particles:
                 initializeParticles(pSystem);
                 numParticlesAlive = pSystem.GetParticles(particles);
             
                 for (int i = 0; i < numParticlesAlive; i++)
                 {
                     //lerp particles to this transform:
                     particles[i].position = Vector3.Lerp(particles[i].position, this.transform.localPosition, Time.deltaTime / speedFactor);
                     Vector3 distanceVector = this.transform.localPosition - particles[i].position;
 
                 // if a particle is in range:
                 if (distanceVector.magnitude <= 10)
                 {
                     var emitOverride = new ParticleSystem.EmitParams();
                     emitOverride.position = particles[i].position;
                     // when this is false, the position is applied perfectly (but doesn't behave like it should). If it's true, the particle is spawned somewhere on the new emittor-shape:
                     emitOverride.applyShapeToPosition = true;
                     particle = particles[i]; 
                     //this doesn't seem to delete the particle :
                     particle.remainingLifetime = -1;
                     orbitPSystem.Emit(emitOverride, 1);
                     Debug.LogError("swapped a particle");
                 }                 
             }
             
                 // Apply the particle changes to the Particle System:
                 pSystem.SetParticles(particles, numParticlesAlive);
             }           
     }
 
     private void initializeParticles(ParticleSystem _pSystem)
     {    
         if (particles == null || particles.Length < _pSystem.main.maxParticles)
             particles = new ParticleSystem.Particle[_pSystem.main.maxParticles];
     }    
 }
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