tools-unity-physics

Unity Physics

Overview

Unity physics handles collision detection, rigidbody simulation, and character movement. This skill covers patterns to prevent common issues like floor penetration.

When to Use

• Character movement and controllers
• Projectile physics
• Collision detection
• Trigger zones
• Ragdoll systems

Character Controller Safety

Preventing Floor Penetration

public class SafeCharacterController : MonoBehaviour
{
    [SerializeField] private float _moveSpeed = 5f;
    [SerializeField] private float _gravity = -20f;
    [SerializeField] private float _groundCheckDistance = 0.1f;
    [SerializeField] private LayerMask _groundLayer;
    
    private CharacterController _controller;
    private Vector3 _velocity;
    private bool _isGrounded;
    
    private void Awake()
    {
        _controller = GetComponent<CharacterController>();
    }
    
    private void Update()
    {
        // Ground check with spherecast for reliability
        _isGrounded = Physics.SphereCast(
            transform.position + Vector3.up * (_controller.radius + 0.1f),
            _controller.radius * 0.9f,
            Vector3.down,
            out _,
            _groundCheckDistance + 0.1f,
            _groundLayer
        );
        
        if (_isGrounded && _velocity.y < 0)
        {
            // Small negative to keep grounded
            _velocity.y = -2f;
        }
        
        // Movement
        Vector3 move = GetMoveInput() * _moveSpeed;
        _controller.Move(move * Time.deltaTime);
        
        // Gravity
        _velocity.y += _gravity * Time.deltaTime;
        _controller.Move(_velocity * Time.deltaTime);
        
        // CRITICAL: Clamp to ground if penetrating
        ClampToGround();
    }
    
    private void ClampToGround()
    {
        if (Physics.Raycast(transform.position + Vector3.up, Vector3.down, out var hit, 2f, _groundLayer))
        {
            if (transform.position.y < hit.point.y)
            {
                transform.position = new Vector3(
                    transform.position.x,
                    hit.point.y,
                    transform.position.z
                );
            }
        }
    }
    
    private Vector3 GetMoveInput()
    {
        float h = Input.GetAxis("Horizontal");
        float v = Input.GetAxis("Vertical");
        return new Vector3(h, 0, v).normalized;
    }
}