🕹️ Lesson 10.4: 2D Physics — A Platformer Base (Mini-Project)

2D Physics Is a Separate Engine

Unity ships two physics engines: 3D (Rigidbody, Collider, Physics) and 2D (Rigidbody2D, Collider2D, Physics2D). They don't interact — a 3D collider won't stop a 2D body. Everything in the 2D track uses the 2D variants, and mixing them up is the most common beginner slip here.

Rigidbody2D & Body Types

A Rigidbody2D hands an object to the physics simulation. Its Body Type decides how:

• Dynamic — fully simulated: gravity, forces, collisions. Your player is Dynamic.
• Kinematic — moved only by script (MovePosition), not by gravity/forces, but still detects collisions. Good for moving platforms and some controllers.
• Static — never moves; the cheap default for level geometry (a Tilemap Collider is effectively static).

Colliders & Feel

Add a Collider2D so the body actually touches things. A Capsule Collider 2D (vertical) is the platformer favourite — its rounded bottom slides over tile seams that a Box collider would snag on. Your tilemap already has a Tilemap Collider 2D + Composite Collider 2D from Lesson 10.3, so the ground is ready.

💡 Physics Materials 2D: assign one with friction = 0 to the player to stop it "sticking" to walls, and tune bounciness if you want springy surfaces.

Moving & Jumping

Read input with the new Input System (Module 3): a Move Vector2 and a Jump button. Set horizontal velocity directly for crisp control, and jump by setting upward velocity. Do physics writes in FixedUpdate:

using UnityEngine;
using UnityEngine.InputSystem;

[RequireComponent(typeof(Rigidbody2D))]
public class PlatformerController2D : MonoBehaviour
{
    [SerializeField] float moveSpeed = 8f;
    [SerializeField] float jumpForce = 14f;

    [Header("Ground Check")]
    [SerializeField] Transform groundCheck;      // an empty at the feet
    [SerializeField] float groundRadius = 0.15f;
    [SerializeField] LayerMask groundLayer;      // set to your "Ground" layer

    Rigidbody2D rb;
    float moveInput;
    bool jumpQueued;
    bool isGrounded;

    void Awake() => rb = GetComponent<Rigidbody2D>();

    // Hooked up via a PlayerInput component (Invoke Unity Events)
    public void OnMove(InputAction.CallbackContext ctx) => moveInput = ctx.ReadValue<Vector2>().x;
    public void OnJump(InputAction.CallbackContext ctx) { if (ctx.performed) jumpQueued = true; }

    void FixedUpdate()
    {
        isGrounded = Physics2D.OverlapCircle(groundCheck.position, groundRadius, groundLayer);

        // horizontal: set velocity directly for responsive control
        rb.linearVelocity = new Vector2(moveInput * moveSpeed, rb.linearVelocity.y);

        if (jumpQueued && isGrounded)
            rb.linearVelocity = new Vector2(rb.linearVelocity.x, jumpForce);

        jumpQueued = false;
    }
}

The Ground Check

You only want to jump when standing on something. The robust way is a tiny overlap circle at the character's feet: if it overlaps anything on the Ground layer, you're grounded. Put an empty child called GroundCheck at the feet and reference it.

The decision each physics step is simple:

Figure 2: Ground check gating the jump.

💡 Feel bonus: add a short coyote time (allow a jump for ~0.1s after leaving a ledge) and jump buffering (remember a press for ~0.1s before landing). These two tricks are what make a platformer feel "tight" instead of stiff.

Mini-Project: The Platformer Base

Summary

🚀 What's Next?

Your character moves — but it's a static sprite sliding around. In Module 11: 2D Animation & Lighting we bring it to life, starting with Lesson 11.1: Frame-Based Sprite Animation — and you'll see the very same Animator state machine from Module 1 driving 2D frames.