Particle collision in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this OnParticleCollision method?

Consider this Unity C# script snippet attached to a GameObject with a Particle System. What will be printed when a particle collides with another GameObject?

Unity

void OnParticleCollision(GameObject other) {
    Debug.Log($"Collided with: {other.name}");
}

A The console prints: "Collided with: " followed by the name of the other GameObject.

B Nothing is printed because OnParticleCollision is never called automatically.

C The console prints "Particle collided" regardless of the other GameObject's name.

D A runtime error occurs because OnParticleCollision requires a ParticleSystem parameter.

💡 Hint

OnParticleCollision is a Unity event method triggered automatically when particles collide with other GameObjects.

The method OnParticleCollision(GameObject other) is called by Unity when particles from the Particle System collide with another GameObject. The parameter other is the GameObject collided with, so the Debug.Log prints its name.

🧠 Conceptual

intermediate

Which component must be enabled for particle collisions to trigger OnParticleCollision?

In Unity, to detect particle collisions and trigger the OnParticleCollision method, which setting must be enabled on the Particle System?

A Set the Particle System's 'Play On Awake' to false.

B Add a Rigidbody component to the Particle System GameObject.

C Enable the 'Collision' module in the Particle System and set 'Send Collision Messages' to true.

D Enable the 'Trigger' module in the Particle System.

💡 Hint

Look for the module that controls particle interactions with other objects.

The 'Collision' module must be enabled and 'Send Collision Messages' checked to allow the Particle System to send collision events that call OnParticleCollision.

🔧 Debug

advanced

Why does this OnParticleCollision method never print anything?

Examine the following code attached to a GameObject with a Particle System. Despite particles colliding with other objects, nothing is printed in the console. What is the most likely cause?

Unity

void OnParticleCollision() {
    Debug.Log("Particle collided");
}

A The Debug.Log statement is inside the wrong method; it should be in Update().

B The Particle System's emission rate is set to zero.

C The Particle System is missing a Collider component.

D The method signature is incorrect; it must have a GameObject parameter to be called.

💡 Hint

Check the method signature required by Unity for particle collision callbacks.

Unity requires the OnParticleCollision method to have a GameObject parameter to be called properly. Without it, the method is not recognized as a collision callback.

📝 Syntax

advanced

Which option correctly implements OnParticleCollision to count collisions?

You want to count how many particles collided with other objects. Which code correctly increments a collision count each time a particle collides?

Unity

int collisionCount = 0;

// Your OnParticleCollision method here

A

void OnParticleCollision(GameObject other) {
    collisionCount++;
}

B

void OnParticleCollision() {
    collisionCount++;
}

C

void OnParticleCollision(GameObject other) {
    collisionCount += other.GetInstanceID();
}

D

void OnParticleCollision(Collider other) {
    collisionCount++;
}

💡 Hint

Check the required method signature and parameter types for OnParticleCollision.

The correct signature is void OnParticleCollision(GameObject other). Option A uses this and increments the count correctly. Option A lacks the parameter, C misuses the parameter, and D uses wrong parameter type.

🚀 Application

expert

How to detect which particles collided and get their positions?

You want to detect each individual particle that collided and get its position during the collision event. Which approach correctly achieves this in Unity?

A Use <code>ParticleSystem.EmitParams.position</code> inside OnParticleCollision to get collided particle positions.

B Use <code>ParticleSystem.GetCollisionEvents(GameObject, List&lt;ParticleCollisionEvent&gt;)</code> inside OnParticleCollision to get collision details including positions.

C Use <code>OnParticleCollision(GameObject other)</code> and access <code>other.transform.position</code> for particle positions.

D Add a Collider to each particle and use OnCollisionEnter to get positions.

💡 Hint

Look for a ParticleSystem method that provides detailed collision event info.

The method GetCollisionEvents returns a list of ParticleCollisionEvent objects, each containing info about individual particle collisions, including the collision point.