Triggers module

Particle Systems have the ability to trigger a Callback whenever they interact with one or more Colliders in the Scene. The Callback can be triggered when a particle enters or exits a Collider, or during the time that a particle is inside or outside of the Collider.

You can use the Callback as a simple way to destroy a particle when it enters the Collider (for example, to prevent raindrops from penetrating a rooftop), or it can be used to modify any or all particles’ properties.

The Triggers module also offers the Kill option to remove particles automatically, and the Ignore option to ignore collision events, shown below.

To use the module, first add the Colliders you wish to create triggers for, then select which events to use.

You can elect to trigger an event whenever the particle is:

• Inside a Collider’s bounds
• Outside a Collider’s bounds
• Entering a Collider’s bounds
• Exiting a Collider’s bounds

Inside the Callback, use ParticlePhysicsExtensions.GetTriggerParticles() (along with the ParticleSystemTriggerEventType you want to specify) to determine which particles meet which criteria.

The example below causes particles to turn red as they enter the Collider, then turn green as they leave the Collider’s bounds.

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

[ExecuteInEditMode]
public class TriggerScript : MonoBehaviour
{
    ParticleSystem ps;

    // these lists are used to contain the particles which match
    // the trigger conditions each frame.
    List<ParticleSystem.Particle> enter = new List<ParticleSystem.Particle>();
    List<ParticleSystem.Particle> exit = new List<ParticleSystem.Particle>();

    void OnEnable()
    {
        ps = GetComponent<ParticleSystem>();
    }

    void OnParticleTrigger()
    {
        // get the particles which matched the trigger conditions this frame
        int numEnter = ps.GetTriggerParticles(ParticleSystemTriggerEventType.Enter, enter);
        int numExit = ps.GetTriggerParticles(ParticleSystemTriggerEventType.Exit, exit);

        // iterate through the particles which entered the trigger and make them red
        for (int i = 0; i < numEnter; i++)
        {
            ParticleSystem.Particle p = enter[i];
            p.startColor = new Color32(255, 0, 0, 255);
            enter[i] = p;
        }

        // iterate through the particles which exited the trigger and make them green
        for (int i = 0; i < numExit; i++)
        {
            ParticleSystem.Particle p = exit[i];
            p.startColor = new Color32(0, 255, 0, 255);
            exit[i] = p;
        }

        // re-assign the modified particles back into the particle system
        ps.SetTriggerParticles(ParticleSystemTriggerEventType.Enter, enter);
        ps.SetTriggerParticles(ParticleSystemTriggerEventType.Exit, exit);
    }
}

The result of this is demonstrated in the images below: