Collision detection is at the heart of every physics-based game in Unity. If you don’t understand it, fast-moving objects may pass through walls, or physics may feel “off.”

Unity provides two main collision detection modes for Rigidbodies: Discrete and Continuous. Choosing the right one is essential for both performance and accuracy.

Discrete Collision Detection

This is the default mode. Unity checks for collisions only at each physics update (FixedUpdate).

• Very efficient
• Perfect for slow-moving objects
• May miss collisions if an object moves too fast → tunneling

Example usage:

Rigidbody rb = GetComponent<Rigidbody>();
rb.collisionDetectionMode = CollisionDetectionMode.Discrete;

Use discrete for most objects that move at moderate speeds or are static most of the time.

Continuous Collision Detection

Continuous mode tells Unity to predict movement between physics steps to catch collisions that might otherwise be missed.

• Prevents fast objects from tunneling through colliders
• More computationally expensive than discrete
• Best for bullets, fast vehicles, or any high-speed Rigidbody

Types of continuous collision detection:

• Continuous: Rigidbody predicts collisions with static colliders.
• Continuous Dynamic: Rigidbody predicts collisions with other dynamic rigidbodies.

Rigidbody rb = GetComponent<Rigidbody>();
rb.collisionDetectionMode = CollisionDetectionMode.Continuous;

When to Use Each Mode

Example: Prevent a Bullet from Passing Through Walls

Rigidbody bulletRb = GetComponent<Rigidbody>();
bulletRb.collisionDetectionMode = CollisionDetectionMode.Continuous;

Without Continuous mode, the bullet might skip the wall entirely if it moves faster than the physics timestep allows.

Performance Considerations

• Discrete is faster and less CPU-intensive
• Continuous increases CPU usage per object
• Use continuous only on objects where tunneling is possible
• Combine with proper Fixed Timestep and physics settings for best results

Common Mistakes

1. Using Continuous on Every Rigidbody

Unnecessary. Only fast-moving objects need it. Overuse can hurt performance.

2. Ignoring Timestep

Even with continuous collision detection, extremely fast objects combined with high physics step intervals can still tunnel.

3. Forgetting Layer Collision Settings

Ensure the fast object’s layer can collide with the target collider.

Debug Checklist

• Is the Rigidbody set to Continuous or Continuous Dynamic?
• Is the object moving fast enough to risk tunneling?
• Is the Fixed Timestep low enough for high-speed physics?
• Are colliders thick enough?

Quick Summary

• Discrete: fast, efficient, may miss collisions → use for most objects
• Continuous: predicts collisions → prevents tunneling, use for fast objects
• Continuous Dynamic: predicts collisions with other moving Rigidbodies
• Balance performance with accuracy

Final Thoughts

Understanding the difference between discrete and continuous collision detection is crucial for high-quality physics in Unity. Fast-moving objects, bullets, vehicles, or anything that could skip colliders must use continuous collision detection.

When combined with proper Rigidbody settings, Fixed Timestep, and good collider design, your game’s physics will be reliable and smooth, without tunneling artifacts.