ParticleSystemRenderer.lengthScale

Description

How much are the particles stretched in their direction of motion, defined as the length of the particle compared to its width.

This determines the base length of particles when they don't move. A value of 1 is neutral, causing no stretching or squashing. Use this with a value greater than 1 to make particles always be longer than they are wide.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {

    private ParticleSystem ps;
    private ParticleSystemRenderer psr;
    public ParticleSystemRenderMode renderMode = ParticleSystemRenderMode.Billboard;
    public float cameraScale = 0.0f;
    public float lengthScale = 0.0f;
    public float velocityScale = 1.0f;

    void Start() {

        ps = GetComponent<ParticleSystem>();
        psr = GetComponent<ParticleSystemRenderer>();

        psr.mesh = Resources.GetBuiltinResource<Mesh>("Capsule.fbx");

        var main = ps.main;
        main.startSpeed = new ParticleSystem.MinMaxCurve(0.5f, 1.5f);
        main.startSize = new ParticleSystem.MinMaxCurve(0.1f, 0.8f);
    }

    void Update() {
        psr.renderMode = renderMode;
        psr.cameraVelocityScale = cameraScale;
        psr.lengthScale = lengthScale;
        psr.velocityScale = velocityScale;

        if (renderMode == ParticleSystemRenderMode.Stretch)
            Camera.main.transform.position = new Vector3(Mathf.Sin(Time.time) * 4.0f, 0.0f, -10.0f);    // move the camera so we can see the effect on stretch camera velocity
    }

    void OnGUI() {
        renderMode = (ParticleSystemRenderMode)GUI.SelectionGrid(new Rect(25, 25, 900, 30), (int)renderMode, new GUIContent[] { new GUIContent("Billboard"), new GUIContent("Stretch"), new GUIContent("HorizontalBillboard"), new GUIContent("VerticalBillboard"), new GUIContent("Mesh"), new GUIContent("None") }, 6);

        if (renderMode == ParticleSystemRenderMode.Stretch) {

            GUI.Label(new Rect(25, 80, 100, 30), "Camera Scale");
            GUI.Label(new Rect(25, 120, 100, 30), "Length Scale");
            GUI.Label(new Rect(25, 160, 100, 30), "Velocity Scale");

            cameraScale = GUI.HorizontalSlider(new Rect(125, 85, 100, 30), cameraScale, 0.0f, 10.0f);
            lengthScale = GUI.HorizontalSlider(new Rect(125, 125, 100, 30), lengthScale, 0.0f, 10.0f);
            velocityScale = GUI.HorizontalSlider(new Rect(125, 165, 100, 30), velocityScale, 0.0f, 10.0f);
        }
    }
}