Question How to implement friction in movement controlled by setting the velocity? (SSB-like physics?)

I am making a party game with Super Smash Bros-like physics. For example, I want the player to slide when they release the Move key.

Here is the code for my player controller:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4. using UnityEngine.InputSystem;
5.  
6. public class PlayerBehavior : MonoBehaviour
7. {
8.     float movementValue = 0f;
9.     [SerializeField] float maxSpeed = 10f;
10.     public Rigidbody2D rb;
11.     CapsuleCollider2D playerCollider;
12.     [SerializeField] float jumpForce = 125f;
13.     [SerializeField] float airControl = 5f;
14.     bool isGrounded;
15.     bool isMoving;
16.     [SerializeField] float groundCheckDistance = 2f;
17.     enum MovementCodeOptions { Default, Simple, Alternate };
18.     [SerializeField] MovementCodeOptions movementCode = MovementCodeOptions.Default;
19.     bool isFacingRight = true;
20.     [SerializeField] float maxDecceleration = 2f;
21.     private void Awake()
22.     {
23.         rb = gameObject.GetComponent<Rigidbody2D>();
24.         playerCollider = gameObject.GetComponent<CapsuleCollider2D>();
25.     }
26.  
27.     private void FixedUpdate()
28.     {
29.         Vector3 debugEndPos = transform.position;
30.         debugEndPos.y -= groundCheckDistance;
31.         Debug.DrawLine(transform.position, debugEndPos, Color.green);
32.         if(Physics2D.Raycast(gameObject.transform.position, Vector2.down, groundCheckDistance, 1 << 3))
33.         {
34.             if (!isGrounded)
35.                 isGrounded = true;
36.             Debug.Log("Player is grounded");
37.         }
38.         else
39.         {
40.             if (isGrounded)
41.                 isGrounded = false;
42.         }
43.         rb.velocity = new Vector2(movementValue * maxSpeed, rb.velocity.y);
44.         if (movementValue == 0 && rb.velocity.magnitude != 0)
45.         {
46.             rb.velocity = new Vector2(rb.velocity.x + (isFacingRight ? -maxDecceleration : maxDecceleration), rb.velocity.y);
47.         }
48.        
49.  
50.         if (movementValue < 0 && isFacingRight)
51.             Flip();
52.         else if (movementValue > 0 && !isFacingRight)
53.             Flip();
54.  
55.         /*if (rb.velocity.magnitude < maxSpeed)
56.         {
57.             rb.AddForce(new Vector2(movementValue * acceleration * Time.deltaTime * 50f, rb.velocity.y));
58.         }*/
59.     }
60.  
61.     void OnMove(InputValue value)
62.     {
63.         movementValue = value.Get<float>();
64.     }
65.  
66.     public void Flip()
67.     {
68.         isFacingRight = !isFacingRight;
69.         transform.localScale = new Vector3(transform.localScale.x * -1, transform.localScale.y, transform.localScale.z);
70.     }
71.  
72.     void OnJump()
73.     {
74.         rb.AddForce(new Vector2(rb.velocity.x, jumpForce), ForceMode2D.Impulse);
75.     }
76.  
77. }
78.  

TL;DR: On line 43, the controller moves the player by setting its rigidbody's velocity directly instead of using AddForce. Therefore, when the player stops moving, it comes to a complete stop instead of sliding to a stop. I don't want to use AddForce because the player accelerates from zero to its max speed instead of instantly starting in its max speed. I just want the player to decelerate when it stops moving. Does anyone know how to do this?
While we're on the subject, how can I make my mid-air movement more like Super Smash Bros.?

 

Maybe you can use Mathf.Lerp.

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class beanController : MonoBehaviour
6. {
7.  
8.     Rigidbody2D RB;
9.  
10.     float horizontalInput = 0f;
11.     [SerializeField] float speed = 20f;
12.     [SerializeField] float damperTime = 0.5f;
13.     float timer = 0f;
14.  
15.  
16.  
17.     private void Start()
18.     {
19.         RB = GetComponent<Rigidbody2D>();
20.     }
21.  
22.     private void Update()
23.     {
24.         horizontalInput = Input.GetAxisRaw("Horizontal");
25.     }
26.  
27.     private void FixedUpdate()
28.     {
29.  
30.         if (horizontalInput != 0f)
31.         {
32.             RB.velocity = new Vector2(horizontalInput * speed, 0f);
33.             timer = 0f;
34.         }
35.         else if(RB.velocity.x != 0f)
36.         {
37.             timer += Time.fixedDeltaTime;
38.  
39.             float newSpeed = Mathf.Lerp(speed, 0f, timer / damperTime);
40.             if (RB.velocity.x < 0)
41.                 newSpeed = -newSpeed;
42.  
43.             RB.velocity = new Vector2(newSpeed, 0f);
44.         }
45.  
46.     }
47.  
48.  
49. }
50.  

Lerp takes 3 parameters a, b and t and returns the value "situated" at a point t between a and b (t must be between 0 and 1, so if it's 0 lerp returns a, if it's 1 lerp returns b). Therefore in my script, as soon as the player stops giving an input a timer starts and with Lerp the velocity goes from a, that is the speed given with the input, and b, that is 0, the final speed: timer / damperTime equals 0 at the beginning, when timer is 0, and 1 at the end, when the timer equals the damperTime, that thus is the duration of the deceleration.