How to apply transform rotations to reflect an object's trajectory in 2D Pong?

Question

I am trying to make a simple 2D Pong game, but I'm unable to get the ball GameObject to move based on its rotation when applying the following logic:

transform.position += transform.forward * Time.deltaTime * ballSpeed;

The above code only changes the ball movement along the z-axis.

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

public class BallMovement : MonoBehaviour
{
    public float ballSpeed = 20f;
    [SerializeField] private Vector3 _rotation;

    void Update()
    {
        transform.position += transform.forward * Time.deltaTime * ballSpeed;
    }

    private void OnCollisionEnter(Collision other)
    {
        _rotation = new Vector3(transform.rotation.x * -1, transform.rotation.y * -1, 0);
        transform.Rotate(_rotation * Time.deltaTime);
    }
}

Answer 1

1. While working with 2 dimensions, try using Vector2, instead of Vector3, as it uses only x and y axes. Then you don't have to deal with the third dimension and it makes things a little bit easier.

2. transform.forward makes your object move forward from the original position on the z axes. That's the blue arrow on your object while using move tool in 3D. Use transform.up, or -transform.up to move up and down, or transform.right, or -transform.right to move rigtht and left.