Translating child to the right whilst maintaining parent's forward movement

Questions & Answers
1

Hi,

I have a child object that I would like to translate to the right by a set distance when it enters a trigger. The child is directly in front of its parent which is translating forwards. I would like to be able to move the child to the right by a set distance without affecting the distance between the parent and child (along Z) after the move - that is, I would like the child to continue moving forward with the parent whilst moving to the new position.

What’s happening with my code below is that when the child begins moving to the right it falls behind the parent and stays there. The script for the parent’s forward translation is on the parent object. The movement is currently executed using a mouse key press to simulate the trigger.

Any guidance would be great.
Thanks

public bool moving = false;

private Vector3 PointA;

private Vector3 PointB;

public float time;

void Update()
{
    if (Input.GetMouseButtonDown(0))
    {
        PointA = transform.position;

        StartCoroutine(MoveFromTo(PointA, PointB, time));

        Debug.Log("Mouse button pressed");
    }
}

IEnumerator MoveFromTo(Vector3 pointA, Vector3 pointB, float time)
{ 
    if (!moving)
    {
        moving = true;

        // Move 10 units to the right - better to use Vector3.right ? 
        Vector3 RightPos = new Vector3(10f, 3, transform.position.z);

        float t = 0f;

        while (t < 1f)
        {                 
            // sweeps from 0 to 1 in time seconds
            t += Time.deltaTime / time;

            pointB = RightPos;

            // set position proportional to t
            transform.position = Vector3.Lerp(pointA, pointB, t);

            // leave the routine and return here in the next frame
            yield return 0;
        }

        // finished moving
        moving = false;
    }
}
2

If you’re moving the child relative to the parent, you should use transform.localPosition instead of transform.position. localPosition is the gameobject’s position relative to its immediate parent, while position is in global space. You also should only modify on the axes that you absolutely need to, and that you can’t inherit from the parent, I think you’ll have no problems then.

EDIT: After a good night’s sleep, I looked at this again and this is what you can do:

void LateUpdate()
{
    if (Input.GetMouseButtonDown(0))
    {
        PointA = transform.localPosition;
        StartCoroutine(MoveFromTo(PointA, PointB, time));
        Debug.Log("Mouse button pressed");
    }
}

IEnumerator MoveFromTo(Vector3 pointA, Vector3 pointB, float time)
{ 
    if (!moving)
    {
        moving = true;

        // Move 10 units to the right - the addition will be local, so this is fine
        Vector3 RightPos = new Vector3(10f, 3, 0);

        float t = 0f;

        while (t < 1f)
        {                 
            t += Time.deltaTime / time;

            pointB = pointA + RightPos;

            transform.localPosition = Vector3.Lerp(pointA, pointB, t);

            yield return 0;
        }

        moving = false;
    }
}

Note that I put this in LateUpdate() to make sure it runs after the parent’s Update() is done in each frame.