Projectile and Ballistics Systems

# CHAPTER 8

Projectile and Ballistics Systems #

1. Introduction #

2. Learning Objectives #

• Differentiate between Hitscan (Raycast) and Physical Projectile systems.

• Implement a Raycast shooting mechanic for instantaneous firearms.

• Instantiate and apply velocity to physical projectiles (rockets/arrows).

• Handle the "Bullet Through Paper" tunneling issue.

• Apply physics-based radial explosion forces to multiple objects.

3. Hitscan Weapons (The Instant Laser) #

• How it works: The exact frame the player pulls the trigger, the CPU draws an invisible line forward. If the line intersects a collider, it instantly registers a hit.

• Pros: 100% accurate, no tunneling bugs, extremely cheap for the CPU.

• Cons: No bullet drop, no travel time. (Not good for bows or rocket launchers).

void ShootHitscan()
{
    RaycastHit hit;
    // Shoot a ray 1000 meters forward from the camera
    if (Physics.Raycast(cameraPos.position, cameraPos.forward, out hit, 1000f))
    {
        Console.WriteLine("Hit: " + hit.collider.name);
        // Apply damage to what we hit
        Health target = hit.collider.GetComponent<Health>();
        if (target != null) target.TakeDamage(10);
    }
}

4. Physical Projectiles (Rockets and Arrows) #

1. 1. Instantiate a Prefab (the missile).

1. 2. Grab its Rigidbody.

1. 3. Apply velocity or AddForce.

1. 4. Let the physics engine handle the arc (gravity) and the impact (OnCollisionEnter).

public GameObject rocketPrefab;
public float rocketSpeed = 50f;

void ShootProjectile()
{
    // Spawn the rocket
    GameObject rocket = Instantiate(rocketPrefab, gunBarrel.position, gunBarrel.rotation);
    
    // Push it forward
    Rigidbody rb = rocket.GetComponent<Rigidbody>();
    rb.velocity = gunBarrel.forward * rocketSpeed;
}

5. Solving the Tunneling Problem #

• The Engine Fix: In the bullet's Rigidbody settings, change "Collision Detection" from Discrete to Continuous Dynamic. This forces the engine to mathematically sweep the space between Frame 1 and Frame 2 to ensure it didn't pass through anything. (Warning: This is CPU-intensive!)

6. Explosions (Radial Force) #

1. 1. Find all objects within a sphere.

1. 2. Apply a force originating from the center of the explosion.

void Explode(Vector3 center, float radius, float force)
{
    // Find all colliders within the blast radius
    Collider[] hitColliders = Physics.OverlapSphere(center, radius);
    
    foreach (Collider hit in hitColliders)
    {
        Rigidbody rb = hit.GetComponent<Rigidbody>();
        if (rb != null)
        {
            // Push them away!
            rb.AddExplosionForce(force, center, radius, 1.0f, ForceMode.Impulse);
        }
    }
}

7. Visual Learning: Hitscan vs Projectile #

[ HITSCAN (Assault Rifle) ]
Player --------(Instantly hits target on Frame 1)--------> Enemy
*No gravity, no travel time.*

[ PROJECTILE (Arrow) ]
Player
  \ Frame 1
   \ Frame 2
    \ Frame 3 (Gravity pulls it down)
     \
      v Enemy
*Takes 1.5 seconds to arrive. Requires leading the target.*

8. Best Practices #

• Fake Bullet Tracers: When using Hitscan, the player still wants to see a bullet. Instantiate a visual "Tracer" particle effect that flies rapidly toward the hit coordinate. The math calculation is already done instantly, but the visual tracer provides the satisfying illusion of a traveling bullet.

9. Common Mistakes #

• Instantiating 100 Bullets a Second: If you are building a minigun using Physical Projectiles, calling Instantiate and Destroy 100 times a second will cause massive Garbage Collection lag. As learned in previous chapters, you MUST use Object Pooling for fast-firing projectile weapons!

10. Mini Project: Build a Grenade #

using System.Collections;

class Grenade : MonoBehaviour
{
    public float delay = 3.0f;
    public float blastRadius = 5.0f;
    public float explosionForce = 700f;

    void Start()
    {
        StartCoroutine(ExplodeSequence());
    }

    IEnumerator ExplodeSequence()
    {
        yield return new WaitForSeconds(delay);

        // 1. Find overlapping physics objects
        Collider[] objectsToPush = Physics.OverlapSphere(transform.position, blastRadius);

        // 2. Apply Force
        foreach (Collider obj in objectsToPush)
        {
            Rigidbody rb = obj.GetComponent<Rigidbody>();
            if (rb != null)
            {
                rb.AddExplosionForce(explosionForce, transform.position, blastRadius);
            }
        }

        // 3. Delete Grenade
        Destroy(gameObject);
    }
}

11. Practice Exercises #

1. 1. What is the definition of a "Hitscan" weapon, and how is it calculated in code?

1. 2. What Rigidbody setting must be changed to prevent a fast-moving physical sniper bullet from phasing through walls?

12. MCQs with Answers #

13. Interview Questions #

• Q: Contrast the CPU performance cost of an assault rifle using Hitscan Raycasts versus an assault rifle firing 60 Physical Rigidbodies a second.

• Q: Explain the "Bullet Through Paper" phenomenon (Tunneling). How does setting a Rigidbody to Continuous Dynamic solve this, and why don't we use that setting for every object in the game?

• Q: Walk me through the code logic required to create a physics-based explosion. How do you find all the objects affected, and how do you apply the force?

14. FAQs #

15. Summary #

16. Next Chapter Recommendation #