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I've been searching for a solution for my problem for a while on the web, but i didn't find anything that work properly

What i want to do

I have a bouncing ball and I want to let the user flick it with his finger (using a swipe gesture or whatever). The ball shouldn't start moving unless the player flick touch the ball. I don't want the ball to move if the player flicks anywhere on the screen, only if the flick touch the ball

What i've done so far :

I've tried to write a script which would detect the touch starting position and the touch end position, and check if the end position is the same as the ball position to make sure that the flick touch the ball. Then the script calculate the direction vector by substrating the start position from the end position. After that i use the AddForce methode and give it the direction vector as a parameter.

Here's my code, (it's better than 1000 words ) :

using UnityEngine;
using System.Collections;

public class Movement : MonoBehaviour
{   
    public Vector2 start;
    public Vector2 end;
    public Vector2 direction;
    public Vector2 ballPos;
    public float Flicktime;
    void Start(){
        }
    void Update(){
        ballPos = new Vector2(transform.position.x,transform.position.y);
        if (Input.touchCount > 0)
        {
            Touch t = Input.touches[0];
            if (t.phase == TouchPhase.Began)
            {
                start = Camera.main.ScreenToWorldPoint(new Vector3(t.position.x,t.position.y,0));
            }

            if (t.phase == TouchPhase.Ended || t.phase == TouchPhase.Canceled)
            {
                end = Camera.main.ScreenToWorldPoint(new Vector3(t.position.x,t.position.y,0));
                direction = end-start ;
                if(t.position == ballPos){

                    rigidbody2D.velocity = direction * 2 ;
                }
            }
        }
    }

}

What's the problem ?

The problem is that the code doesn't work.

When i launch the game in the Unity Remote 4 app in my android device and try to flick the ball it doesn't move, the inspector shows that the the scripte is calculating the start & end positions and the direction vector, but the ball doesn't move, it stays in the same position even when the flick touch the ball.

So what's the problem ? is there a better way to do it ?

Since the ball have a circle collider how to make it detect collision with the player swipe ?

Thank's and have a nice weekend !

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t.position == ballPos is causing all your issue. You are comparing 2 vectors which will never be the same. The player will never tap exactly where the ball is. You should either do a HitTest or a Physics2D.OverlapPoint

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Since you want the ball to only do something on touch I would remove all that and put your movement code in a OnMouseDown() it will still react to a tap. Depending on how you have it set up and if that works for you it might be a better way to accomplish your task.

The reason your code is not working is because the position you tap is not == to the balls position.

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Try replacing these lines:

if (Input.touchCount > 0)
    {
        Touch t = Input.touches[0];
        if (t.phase == TouchPhase.Began)
        {
            start = Camera.main.ScreenToWorldPoint(new Vector3(t.position.x,t.position.y,0));
        }

        if (t.phase == TouchPhase.Ended || t.phase == TouchPhase.Canceled)
        {
            end = Camera.main.ScreenToWorldPoint(new Vector3(t.position.x,t.position.y,0));
            direction = end-start ;
            if(t.position == ballPos){

                rigidbody2D.velocity = direction * 2 ;
            }
        }
    }

You can use Touch.deltaPosition to find the swipe distance and direction. Also check a HitTest with the ball texture to know whether we're touching the ball.

Vector2 swipeDistance;
Texture ballTexture;

if (Input.touchCount > 0)
{
    Touch t = Input.touches[0];

    if (t.phase == TouchPhase.Ended || t.phase == TouchPhase.Canceled)
    {
        swipeDistance = t.deltaPosition;

        if(myTexture.HitTest(t.position))
            rigidbody2D.velocity = direction * 2 ;
    }
}
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