Physics-compliant 2D Platformer Movement in Unity using Rigidbody2D

Movement.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[RequireComponent(typeof(Rigidbody2D))]
public class Movement : MonoBehaviour
{
    // Rigidbody contained on the object this script is attached to.
    private Rigidbody2D rb;

    // Player size and ground detection for jumping.
    public Vector2 PlayerSize = new Vector2(1f, 1f);
    public float GroundDetectionLength = 0.1f;

    // Movement settings.
    public float Acceleration = 2;
    public float MaxSpeed = 8;
    public float GroundFriction = 1;
    public float JumpHeight = 3f;

    // Transfers jump button to fixedUpdate.
    private bool JumpPressed = false;

    void Start()
    {
        // Get the rigidbody.
        rb = GetComponent<Rigidbody2D>();
    }

    void Update()
    {
        // If jump button is pressed, set jump pressed to true.
        if (Input.GetButtonDown("Jump"))
            JumpPressed = true;
    }

    void FixedUpdate()
    {
        // Scale acceleration by target velocity and clamp it between 0 and Accelleration.
        float scaledAcceleration = Acceleration * (1 - Mathf.Abs(rb.velocity.x) / MaxSpeed);

        // Simulate friction. 
        if (rb.velocity.x > 0)
            rb.velocity = new Vector2(rb.velocity.x - Mathf.Min(GroundFriction, rb.velocity.x), rb.velocity.y); // Velocity is positive.
        else if (rb.velocity.x < 0)
            rb.velocity = new Vector2(rb.velocity.x - Mathf.Max(-GroundFriction, rb.velocity.x), rb.velocity.y); // Velocity is negative.

        // Add scaled acceleration to velocity in the direction of the horizontal axis.
        rb.velocity += new Vector2(scaledAcceleration * Input.GetAxis("Horizontal"), 0);
        // Simulate jumping.
        if(JumpPressed && CheckIsGrounded())
        {
            JumpPressed = false;
            rb.AddForce(Vector2.up * JumpHeight);
        }
        
    }

    /// <summary>
    /// Checks if this object is grounded based on defined PlayerSize field.
    /// </summary>
    bool CheckIsGrounded()
    {
        // Check what is below us.
        RaycastHit2D[] collisions = Physics2D.BoxCastAll(rb.position, PlayerSize, rb.rotation, transform.TransformDirection(Vector2.down), GroundDetectionLength);

        // Check if any of the collided objects are solid.
        foreach(RaycastHit2D hit in collisions)
        {
            // Get the collider and check if its solid and not the current game object.
            if (!hit.collider.isTrigger && hit.collider.gameObject != gameObject)
                return true;
        }
        // If nothing was a trigger, return false.
        return false;
    }

    /// <summary>
    /// Draws the character PlayerSize box and the ground detection box.
    /// </summary>
    private void OnDrawGizmosSelected()
    {
        // Change drawing matrix to local space.
        Gizmos.matrix = transform.localToWorldMatrix;

        // Draw the character shape.
        Gizmos.color = new Color(.68f, .04f, .37f); // Purple
        Gizmos.DrawWireCube(Vector2.zero, PlayerSize);

        // Draw the ground detection length.
        Gizmos.color = new Color(1f, .74f, 0f); // Orange
        Gizmos.DrawWireCube(Vector2.zero - new Vector2(0, PlayerSize.y / 2 + GroundDetectionLength / 2), new Vector2(PlayerSize.x, GroundDetectionLength));
    }

}