ParticleSystem.TrailModule.ratio

Description

Choose what proportion of particles will receive a trail.

Use a value between 0 and 1, where 0 will add trails to no particles, and 1 will add trails to all particles.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    private ParticleSystem ps;
    public float hSliderValueRatio = 1.0f;

    void Start()
    {
        ps = GetComponent<ParticleSystem>();

        var main = ps.main;
        main.startColor = new ParticleSystem.MinMaxGradient(Color.red, Color.yellow);
        main.startSize = 0.1f;

        var trails = ps.trails;
        trails.enabled = true;

        var psr = GetComponent<ParticleSystemRenderer>();
        psr.trailMaterial = new Material(Shader.Find("Sprites/Default"));
    }

    void Update()
    {
        var trails = ps.trails;
        trails.ratio = hSliderValueRatio;
    }

    void OnGUI()
    {
        GUI.Label(new Rect(25, 40, 100, 30), "Ratio");

        hSliderValueRatio = GUI.HorizontalSlider(new Rect(55, 45, 100, 30), hSliderValueRatio, 0.0f, 1.0f);
    }
}