Restricting movement of a 2d object to backward only in UNITY - unity3d

Question

I'm making a simple project in Unity where there is a Ball attached to a SpringJoint2d component the ball is on an angled slope, like in the image below:
I simply want the user to be able to drag the ball backward along the edge of the slope only,in other words I don't want the user to be able to move the ball away from the slope or into it.
I'v been trying several ways I thought could do the job hers the script of the dragging with what I tried:
(This Is the updated version)
public class ball : MonoBehaviour
{
public Rigidbody2D rb;
public Transform spring;
public Transform calcpoint;
private Vector3 start;
private Vector3 end;
private bool isPressed = false;
RaycastHit2D[] hits = new RaycastHit2D[2];
RaycastHit2D[] hits2 = new RaycastHit2D[2];
float factor = 0;
private void OnMouseDown()
{
if (!isPressed)
{
isPressed = true;
rb.isKinematic = true;
}
}
private void OnMouseUp()
{
isPressed = false;
rb.isKinematic = false;
StartCoroutine(release());
}
/// <summary>
/// release the ball from the spring joint after a small amount of time
/// </summary>
/// <returns></returns>
IEnumerator release()
{
yield return new WaitForSeconds(0.1f);
rb.GetComponent<SpringJoint2D>().enabled = false;
}
// Update is called once per frame
void Update()
{
if (isPressed)
{
if (Vector3.Distance(spring.position, rb.position) > 3f || spring.position.x < (rb.position.x - 1)) return;//restrict the dragging of the ball to not go beyond the spring point and not too far back
float angle = 0;
if (checkGround() > 1)//if we hit the slope with the ray cast downward from the mouse/Tap position
{
angle = Mathf.Abs(Mathf.Atan2(hits[1].normal.x, hits[1].normal.y) * Mathf.Rad2Deg); //get angle
factor = (float)(((45 - angle) * 0.02) + 1) * (angle / 45);//an inaccurate formula to offset the ball to be on top of the slope that works just fine with some glitches
rb.position = hits[1].point + new Vector2(0, factor * 1f);//position the ball at the point were the ray cast downward from the mouse hit
//(that puts the ball center on the line of the slope) so I offset it usinf the formula above
}
}
}
private int checkGround()
{
int h = Physics2D.RaycastNonAlloc(Camera.main.ScreenToWorldPoint(Input.mousePosition), -Vector2.up, hits); //cast downwards
return h;
}
}
here are the settings on the ball:
and the slope setup:
The dragging of the ball works fine ,at one point the player could drag it in the air or into the slope, I managed to fix that with the new code so now the player could only drag it on the edge, though my calculations are still a bit flawed and when the slopes angle is changed the ball would dip a bit inside the slope and that causes some problems at release.
The method used to try to solve the problem is simple, when the player start dragging the ball I cast a ray from the mouse downward and pit the ball on the point of impact with the slope ,offsetting it to sit on top of it,right ow the problem is that the offsetting part is not accurate enough.
I hope I explained myself a bit better this time Thanks:)

Answer 1

After lots of trial and error I did manage to come up with a perfect solution to the problem so I thought I might as well share the answer maybe it will help someone.
here is the updated code I changed my method of restricting the movement completely now I use simple linear line equation as shown below:
private void OnMouseDown()
{
if (!isPressed)
{
//cast a ray on the slope
if (checkGround() > 1)
{
angle = Mathf.Abs(Mathf.Atan2(hits[1].normal.x, hits[1].normal.y) * Mathf.Rad2Deg); //get angle
slope = Mathf.Tan(angle * Mathf.Deg2Rad);//get the slope steepiness
}
isPressed = true;
rb.isKinematic = true;
}
}
private void OnMouseUp()
{
isPressed = false;
rb.isKinematic = false;
StartCoroutine(release());
}
void Update() {
if (isPressed)
{
xMove = Camera.main.ScreenToWorldPoint(Input.mousePosition).x - spring.position.x;//get how much the mouse moved backward or forward
if (xMove < -3f ) xMove = -3f; //restrict the drag range to 3 backward
if (xMove > 0.3f) xMove = 0.3f;//restrict the drag range to 0.3 forward
xpos = spring.position.x+xMove;//since the ball and the spring start at exactly the same position the new ball's x position would be the spring x + the x movement we calculated above
ypos = (xMove * slope)- spring.position.y; //the y posistion would be y=mx+b so the the x movement * the slop steepiness - the starting y position
rb.position = new Vector2(xpos, -ypos);//set the new position of the ball
}
}
private int checkGround()
{
int h = Physics2D.RaycastNonAlloc(Camera.main.ScreenToWorldPoint(Input.mousePosition), -Vector2.up, hits); //cast downwards
return h;
}