Invert ParticleEffect Velocity

파티클 이펙트를 런타임 중에 방향을 반전 시키는 간단한 스크립트.

생성 될 때 방향을 반전시키기 위해서 ParticleSystem.startSpeed 를 반전 시키고,

이미 생성 된 파티클은 ParticleSystem.Particle.velocity 를 반전 시켜 줌.

using UnityEngine;
using System.Collections;

public class InvertParticleEffect : MonoBehaviour
{
    ParticleSystem m_System;
    ParticleSystem.Particle[] m_Particles;


    void InitializeIfNeeded()
    {
        if (m_System == null)
            m_System = GetComponent();

        if (m_Particles == null || m_Particles.Length < m_System.maxParticles)
            m_Particles = new ParticleSystem.Particle[m_System.maxParticles];
    }

    public void Invert()
    {
        InitializeIfNeeded();

        // 생성될 때, 파티클 Speed 방향 반전
        var vel = m_System.startSpeed *= -1f;

        // GetParticles is allocation free because we reuse the m_Particles buffer between updates
        int numParticlesAlive = m_System.GetParticles(m_Particles);

        // Change only the particles that are alive
        for (int i = 0; i < numParticlesAlive; i++)
        {
            // 이미 생성된 파티클은 velocity 반전해서 반대로 가도록..
            m_Particles[i].velocity *= -1f;
        }

        // Apply the particle changes to the particle system
        m_System.SetParticles(m_Particles, numParticlesAlive);
    }

}

[참조] https://docs.unity3d.com/ScriptReference/ParticleSystem.GetParticles.html

[참조] https://docs.unity3d.com/ScriptReference/ParticleSystem-startSpeed.html