Improvement by jannysice

Top Down Movement - normalized 2D.cs

using UnityEngine;

public class TopDownMovement : MonoBehaviour {

	public float walkSpeed = 5f;
	public Boundary boundary; // optional rectangle boundary

	float maxSpeed = 10f;
	float curSpeed;

	float sprintSpeed;
	Rigidbody rb;
 
	void Start() {
		rb = GetComponent<Rigidbody>();
		// sprintSpeed = walkSpeed + (walkSpeed / 2);
	}
 
	void FixedUpdate() {
		curSpeed = walkSpeed;
		maxSpeed = curSpeed;

		//Normalize movement vector so diagonal movement is not twice as fast.
		float xDir = Input.GetAxis("Horizontal"), zDir = Input.GetAxis("Vertical");
		Vector2 movement = new Vector2(xDir,zDir).normalized;
		
		// the movement magic
		rb.velocity = new Vector3(
			Mathf.Lerp(0, movement.x* curSpeed, 0.8f),
			rb.velocity.y,
			Mathf.Lerp(0, movement.y* curSpeed, 0.8f)
		);
    
               // optional: clamp position inside a rectangle
		rb.position = new Vector3(
			Mathf.Clamp(rb.position.x, boundary.xMin, boundary.xMax),
			rb.position.y,
			Mathf.Clamp(rb.position.z, boundary.zMin, boundary.zMax)
		);
	}
}

// optional rectangle boundary
[System.Serializable]
public struct Boundary {
	public float xMin;
	public float xMax;
	public float zMin;
	public float zMax;
}