proto_racer/Assets/Scripts/CarLogic.cs

using Unity.Mathematics;
using UnityEngine;
using UnityEngine.InputSystem;

[RequireComponent(typeof(Rigidbody2D))]
public class CarLogic : MonoBehaviour
{
	public InputAction steeringAction;
	public InputAction accelerationAction;
	public InputAction brakeAction;

	public float accelerationAmount = 10;
	[Tooltip("In degrees")] 
	public float steeringAnglePerSecond = 10;

	public float maxAcceleration = 100;
	public float brakingAmount;

	private Rigidbody2D _rigidbody;
	private Transform _transform;
	private float _currentAcceleration;
	private float _wheelAccelerationAmount;
	private int _wheelOffroadCount = 0;

	public float CurrentAccelerationRatio()
	{
		return _currentAcceleration / maxAcceleration;
	}
	
	private void Awake()
	{
		_rigidbody = GetComponent<Rigidbody2D>();
		_transform = transform;
	}

	private void Start()
	{
		steeringAction.Enable();
		accelerationAction.Enable();
		brakeAction.Enable();

		var wheels = GetComponentsInChildren<Wheel>();
		foreach (var wheel in wheels)
		{
			wheel.wheelOffRoad = WheelOffRoad;
			wheel.wheelOnRoad = WheelOnRoad;
		}

		_wheelAccelerationAmount = maxAcceleration / 5f;
		_wheelOffroadCount = 4;
	}

	private void WheelOffRoad()
	{
		_wheelOffroadCount++;
	}

	private void WheelOnRoad()
	{
		_wheelOffroadCount--;
	}

	private void Update()
	{
		var steeringValue = steeringAction.ReadValue<float>();
		var accelerationValue = accelerationAction.ReadValue<float>();
		var brakeValue = brakeAction.ReadValue<float>();
		// TODO: The way that I changed this too I like a lot better, however I do want to eventually figure out what was wrong with this verbose approach.
		// Vector2 velocityDir = _transform.up;
		// var currentAngleRad = Mathf.Acos(Vector3.Dot(velocityDir, Vector3.up));
		// var deltaAngleRad = steeringValue * steeringAnglePerSecond * Time.deltaTime * Mathf.Deg2Rad;
		// var angleRad = deltaAngleRad + currentAngleRad;
		//
		// var angleCos = Mathf.Cos(angleRad);
		// var angleSin = Mathf.Sin(angleRad);
		// Vector2 nextVelocityDir;
		// nextVelocityDir.x = angleCos * velocityDir.x -
		//                     angleSin * velocityDir.y;
		// nextVelocityDir.y = angleSin * velocityDir.x +
		//                     angleCos * velocityDir.y;
		//
		// nextVelocityDir *= accelerationAmount * accelerationValue * Time.deltaTime;

		// TODO: probably not correct... ODE or some other formula.
		if (accelerationValue <= 0)
		{
			_currentAcceleration -= _rigidbody.drag * Time.deltaTime;
		}

		_currentAcceleration += accelerationValue * accelerationAmount * Time.deltaTime;
		
		_currentAcceleration -= brakeValue * brakingAmount * Time.deltaTime;

		if (_currentAcceleration > maxAcceleration / 3f)
		{
			_currentAcceleration -= _wheelOffroadCount * _wheelAccelerationAmount * Time.deltaTime;
		}

		// TODO: reverse logic.
		_currentAcceleration = Mathf.Clamp(_currentAcceleration, 0, maxAcceleration);
		
		if (_currentAcceleration > 0.01)
		{
			var newAngle = steeringValue * steeringAnglePerSecond * Time.deltaTime;
			_transform.Rotate(Vector3.forward, newAngle, Space.World);
		}

		_rigidbody.velocity = _transform.up * _currentAcceleration;
	}
}