How do I find what direction an object is traveling between updates

Questions & Answers
1

I am building a Pong game. and the player has the ability to catch the ball with the paddle by holding down the space bar. The paddles move up and down on the y axes by using the up and down arrows. After the player releases the space bar I would like to figure if the paddle is traveling up or down and “throw” the ball in the direction of travel of the paddle. I’m having a hard time being able to record the paddles Y position between updates because the function for throwing seems to happen a lot faster than the frame rate.

Here is my code for the ball and how I’m trying to throw it.

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

public class BallController : MonoBehaviour {
	
	private PaddleController _paddle;
	private bool hasStarted = false;
    private Vector3 paddleLastKnownPosition;


	// Use this for initialization
	void Start () {

        InvokeRepeating("StartBall", 2f, 1f);

	}
	
	// Update is called once per frame
	void Update () {


	    if (_paddle)
	    {

	        HoldToPaddle();
            paddleLastKnownPosition = _paddle.transform.position;
        }
		
	}

   

    private void HoldToPaddle()
    {
        Vector3 ballPos = new Vector3(transform.position.x, transform.position.y);
        ballPos.y = _paddle.transform.position.y;
        transform.position = ballPos;

    }

    void StartBall()
    {
       GetComponent<Rigidbody2D>().velocity = new Vector2(-15f, 5f);
       CancelInvoke("StartBall");
    }

    void OnCollisionEnter2D(Collision2D collision)
    {
        Vector2 tweak = new Vector2(Random.Range(0f, 0.1f), Random.Range(0f, 0.1f));
        if (hasStarted)
        {
            GetComponent<AudioSource>().Play();
            GetComponent<Rigidbody2D>().velocity += tweak;
        }
    }

    //let's the ball know that it's caught when the space bar is held down and it colides with the paddle
    public void Caught(PaddleController paddle)
    {
        _paddle = paddle;
        GetComponent<Rigidbody2D>().velocity = new Vector2(0, 0);
        HoldToPaddle();
    }


    //throw ball when space bar is let go
    public void Throw()
    {
        float xVelocity = -15f;
        float yVelocity = 5f;

        if (_paddle.transform.position.x < 0f)
        {
            xVelocity = -xVelocity;
        }

        print(paddleLastKnownPosition.y + " : " + _paddle.transform.position.y);
        if (_paddle.transform.position.y > paddleLastKnownPosition.y)
        {
            yVelocity = -yVelocity;
        }
        else if (_paddle.transform.position.y < 0f)
        {
            yVelocity = -yVelocity;
        }

        GetComponent<Rigidbody2D>().velocity = new Vector2(xVelocity, yVelocity);
        _paddle = null;
    }
}
2

I would store the last position, but not actually use it. Instead, I would have additional difference variable which gets calculated before the last position is overwritten. So the code in Update would look something like this:

difference = _paddle.transform.position - lastPosition;
lastPosition = _paddle.transform.position:

Then just use the difference value. If you need to get velocity, then just divide the difference by the deltaTime.