Why does my gameobject fly of into the air when the screen is touched?

Question

I am encountering a peculiar problem when updating a piece of code that translates my gameobject left and right based on mobile touch input.

To provide context, the platform upon which the gameobject, which is a sphere in my case, translates, is this:

The platform is 10 units wide, with the sphere in the center.

In its original form, the code looks like this:

void FixedUpdate () {
    if(Input.touchCount == 1) { 
        float touchXComponent = Input.GetTouch(0).deltaPosition.x;            
        transform.Translate(Vector3.right * Time.smoothDeltaTime * touchXComponent * 0.5f);
    }
}

It provides the desired left and right movement, but it has a tendency to allow the ball to leave the platform, and then start moving up and down in the air with each further touch.

To combat that, I tried editing the code as follows:

void FixedUpdate(){
    if (Input.touchCount == 1){
        float touchXComponent = Input.GetTouch(0).deltaPosition.x;
        transform.Translate((Vector3.right * Time.smoothDeltaTime * touchXComponent * 0.5f).x, transform.position.y, transform.position.z);
    }
}

This, however, causes the ball to fly of the screen the second it is touched, leaving me with this error in the console:

Assertion failed: Invalid worldAABB. Object is too large or too far away from the origin.

I would have thought that the update I made to the code would keep the ball stationary on the y and z-axes, while allowing it to translate freely on the x-axis. Why is that not the case?

Thank you.

Answer 1

As this doc says :

If relativeTo is left out or set to Space.Self the movement is applied relative to the transform's local axes.

Which means you're actually translating your object by it's own position every update. To avoid that just change your call to :

transform.Translate((Vector3.right * Time.smoothDeltaTime * touchXComponent * 0.5f).x, 0, 0);

Answer 2

From what I understand, you want the ball to move on the X axis only, relative to world coordinates. The current method you're using will do it in the local coordinates (relative to the object).

Since Transform.Translate method already gives you this functionality, you can just change your line from

transform.Translate((Vector3.right * Time.smoothDeltaTime * touchXComponent * 0.5f).x, transform.position.y, transform.position.z);

to

transform.Translate((Vector3.right * Time.smoothDeltaTime * touchXComponent * 0.5f).x, transform.position.y, transform.position.z, Space.World);

and it should work in theory (I don't have access to Unity right now).