ParticleSystemRenderer.flip

Description

Flip a percentage of the particles, along each axis.

Set between 0 and 1, where higher values cause a higher proportion of the particles to be flipped, and 1 causes all particles to be flipped.

using UnityEngine;
using UnityEditor;
using System.Collections;

public class ExampleClass : MonoBehaviour {

    private ParticleSystemRenderer psr;
    public Vector3 flip;

    void Start() {

        psr = GetComponent<ParticleSystemRenderer>();

        psr.material = AssetDatabase.GetBuiltinExtraResource<Material>("Default-Diffuse.mat");  // square material so we can see the pivot more easily
        psr.mesh = Resources.GetBuiltinResource<Mesh>("Capsule.fbx");
    }

    void Update() {

        psr.flip = flip;
    }

    void OnGUI() {

        GUI.Label(new Rect(25, 40, 100, 30), "X");
        GUI.Label(new Rect(25, 80, 100, 30), "Y");
        GUI.Label(new Rect(25, 120, 100, 30), "Z");

        flip.x = GUI.HorizontalSlider(new Rect(65, 25, 100, 30), flip.x, 0.0f, 1.0f);
        flip.y = GUI.HorizontalSlider(new Rect(65, 65, 100, 30), flip.y, 0.0f, 1.0f);
        flip.z = GUI.HorizontalSlider(new Rect(65, 105, 100, 30), flip.z, 0.0f, 1.0f);
    }
}