Physics

Raycasting

Raycasting casts an invisible ray in a direction to find Colliders — the foundation of shooting, ground checks, mouse picking, and line-of-sight gameplay.

Imagine...

A Raycast is a flashlight in the dark. You shine it one way — the beam travels until it hits something. Then it reports what it hit, how far, where, and which way the surface faces. In a shooter, a Raycast stands in for a real physics bullet — cheaper, faster, more precise.

The concept in detail

Physics.Raycast() takes an origin, a direction, and returns true if the ray hits a Collider. Details land in a RaycastHit: hit position ( .point), surface direction (.normal), distance ( .distance), and the object (.collider).

Unity ships several variants: Physics.RaycastAll() returns every Collider along the path (not just the nearest), Physics.SphereCast() sweeps a sphere (smoother character “snapping”), and Physics.BoxCast() sweeps a box. From Unity 2022+, Physics.RaycastCommand can run raycasts in parallel on the Job System.

Performance: Raycasts are not free — each call walks the broadphase BVH. Always pass a LayerMask and a maxDistance. Avoid looping them every frame — an AI can raycast 4 directions every 0.2s instead of every frame.

Common uses: shooting (hitscan, no Rigidbody bullet), ground check (is the character standing before a jump), mouse picking ( Camera.ScreenPointToRay() turns a click into a 3D ray), line of sight (does anything block the AI from the player).

Raycast variants

Raycast

A straight ray; returns only the nearest Collider. Use it for almost everything.

Physics.Raycast()

SphereCast

A spherical sweep — better for characters, large weapons, and wide-area detection.

Physics.SphereCast()

RaycastAll

Returns all Colliders along the path. Use for armor-piercing bullets, lights through glass.

Physics.RaycastAll()

Hands-on steps

Pick origin and direction

Often Camera.main.transform.position and .forward for FPS, or Vector3.down for a ground check.

Declare a RaycastHit

RaycastHit hit; — then pass out hit into Physics.Raycast(). Keep it outside Update to avoid GC.

Set a LayerMask

Assign it in the Inspector, or LayerMask.GetMask("Enemy", "Ground") so you only test what you need.

Cap maxDistance

Always pass a max range — an infinite ray tests the whole scene. Example: gun range 50f, ground check 1.2f.

Draw a Debug Ray in Scene view

Debug.DrawRay(origin, direction * maxDist, Color.green) — visible while playing, no effect in builds.

Interactive simulator

Move the mouse over the canvas to aim the ray. Drag obstacles around.

Multi-RayMove the mouse...

No hit yet

Code example

Basic

Hitscan shooting — fire without a Rigidbody bullet.

using UnityEngine;

public class HitscanGun : MonoBehaviour
{
  public float range = 50f;
  public int damage = 25;
  public LayerMask shootMask;
  public ParticleSystem muzzleFlash;

  Camera cam;
  RaycastHit hit; // Declare outside Update to avoid GC

  void Start() => cam = Camera.main;

  void Update()
  {
      if (Input.GetButtonDown("Fire1")) Fire();
  }

  void Fire()
  {
      muzzleFlash.Play();

      // Ray from camera center, forward
      if (Physics.Raycast(cam.transform.position,
                         cam.transform.forward,
                         out hit, range, shootMask))
      {
          Debug.Log("Hit: " + hit.collider.name +
                     " at " + hit.distance.ToString("F1") + "m");

          hit.collider.GetComponent<Health>()
             ?.TakeDamage(damage);
      }
  }
}

Code example

Advanced

Accurate ground check plus mouse-to-world picking — the two most common use cases.

using UnityEngine;

public class RaycastUtils : MonoBehaviour
{
  [Header("Ground Check")]
  public float groundCheckDist = 1.2f;
  public LayerMask groundLayer;
  bool isGrounded;

  [Header("Mouse Picking")]
  public LayerMask clickable;

  Camera cam;
  RaycastHit hit;

  void Awake() => cam = Camera.main;

  void Update()
  {
      // Ground check every frame — SphereCast is smoother than Raycast
      isGrounded = Physics.SphereCast(
          transform.position, 0.4f,
          Vector3.down, out hit,
          groundCheckDist, groundLayer
      );

      // Click → world position
      if (Input.GetMouseButtonDown(0))
      {
          Ray ray = cam.ScreenPointToRay(Input.mousePosition);
          if (Physics.Raycast(ray, out hit, 100f, clickable))
          {
              Debug.Log("Clicked: " + hit.collider.name);
              // Move the character to hit.point
              MoveTo(hit.point);
          }
      }
  }

  void OnDrawGizmosSelected()
  {
      Gizmos.color = isGrounded ? Color.green : Color.red;
      Gizmos.DrawLine(transform.position,
          transform.position + Vector3.down * groundCheckDist);
  }
}

📌 Quick recap

▸Always pass a LayerMask + maxDistance
▸Declare RaycastHit once outside Update (avoid GC)
▸Camera.ScreenPointToRay() for mouse-to-3D
▸Debug.DrawRay() to see the ray in Scene view
▸SphereCast is smoother than Raycast for character movement

⚠️ Common mistakes

❌ The ray hits yourself (self-hit)
Origin sits inside the shooter’s Collider — always returns true
✅ Offset the origin (+0.1f along forward), or ignore your own layer
❌ Raycast every frame with no MaxDistance
An infinite ray tests the whole scene and tanks FPS
✅ Always pass a maxDistance that matches the use case