Space dust particles

SpaceDust.cs

using UnityEngine;
using System.Collections;

public class SpaceDust : MonoBehaviour
{
    public float m_Size = 1.0f;             // Halfwidth of the particle volume
    public float m_MinBrightness = 0.2f;
    public float m_MaxBrightness = 1.0f;

    protected ParticleEmitter m_ParticleEmitter;
    protected Particle[] m_Particles;
    protected int m_NumParticles;

    protected float m_TotalWidth;

    protected Vector3 m_PreviousPosition;
    protected Vector3 m_Direction;

    protected void Start()
    {
        m_ParticleEmitter = particleEmitter;
        m_NumParticles = (int)m_ParticleEmitter.maxEmission;
        m_Particles = new Particle[m_NumParticles];

        m_TotalWidth = m_Size * 2.0f;
        Vector3 transformPosition = transform.position;
        for(int index = 0; index < m_NumParticles; ++index)
        {
            Particle particle = new Particle();

            particle.position = transformPosition + new Vector3(
                Random.value * m_TotalWidth - m_Size, Random.value * m_TotalWidth - m_Size, Random.value * m_TotalWidth - m_Size);

            particle.energy = 1.0f;
            particle.size = Random.Range(m_ParticleEmitter.minSize, m_ParticleEmitter.maxSize);
            particle.color = Color.white * Random.Range(m_MinBrightness, m_MaxBrightness);

            m_Particles[index] = particle;
        }
    }

    protected void FixedUpdate()
    {
        // This works better than Camera.velocity when the camera is being moved in FixedUpdate:

        m_Direction = m_PreviousPosition - transform.position;
        m_PreviousPosition = transform.position;
    }

    protected void LateUpdate()
    {
        Vector3 transformPosition = transform.position;

        for(int index = 0; index < m_NumParticles; ++index)
        {
            Vector3 particlePosition = m_Particles[index].position;
            Vector3 offset = transformPosition - particlePosition;

            if(offset.x > m_Size)
                particlePosition.x += m_TotalWidth;
            else if(offset.x < -m_Size)
                particlePosition.x -= m_TotalWidth;
            
            if(offset.y > m_Size)
                particlePosition.y += m_TotalWidth;
            else if(offset.y < -m_Size)
                particlePosition.y -= m_TotalWidth;

            if(offset.z > m_Size)
                particlePosition.z += m_TotalWidth;
            else if(offset.z < -m_Size)
                particlePosition.z -= m_TotalWidth;

            m_Particles[index].position = particlePosition;
            m_Particles[index].velocity = m_Direction;
        }

        m_ParticleEmitter.particles = m_Particles;
    }
}