Shrink a rotating object up to point

Question

I have an object (orange) that is tied to a hinge joint (black) and can rotate around it. At some point when I detect collision with other object I have to cut it there (red). In order to do that I want to shrink the object between those points (black and red), but I need it to remain tied to the hinge joint and to keep its width.

void OnCollisionEnter2D(Collision2D collision)
{
    GameObject obj = collision.gameObject;
    Vector3 endPos =collision.contacts[0].point;
    float scaleX = Vector3.Distance(new Vector3(startPos.x, 0, 0), new Vector3(endPos.x, 0, 0));
    float scaleY = Vector3.Distance(new Vector3(0, startPos.y, 0), new Vector3(0, endPos.y, 0));
    Vector3 newScale = new Vector3(scaleX,scaleY, 1);
    obj.transform.parent.transform.localScale = obj.transform.TransformPoint(newScale);
}

And the start position is initialized by the position of the hinge joint:

startPos = GameObject.Find("hair").GetComponent<HingeJoint2D>().transform.position;

I wrapped the object in parent and scaled it, because I read somewhere that then it would remain in place:

I tried many things, but I can’t get it to stay in place and be in right size. How can I implement it right?

What is startPos? How are the transform components of the orange object and its parent nodes arranged? Is it a simple sprite or something else? How do you want to shrink it? It looks like a curly stick, but I saw you scaled both x and y coords of the parent's transform, I don't understand this. — shingo
– shingo, Commented Jun 4, 2024 at 9:10
I added the details in the question. And I do use the y, because the object may be rotated to any angle. how else should I calculate it's new scale? @shingo — flowerProgrammer
– flowerProgrammer, Commented Jun 4, 2024 at 9:24
Have you tried to change only y scale and the pivot of the sprite? Can you add more details like the position of each node, and where the connected rigidbody is? — shingo
– shingo, Commented Jun 4, 2024 at 11:26
Your problem at its core stems from the pivot point of that object, as @azelito pointed out. If you set that right, scaling works as you expect it. Understanding pivot points (or anchors) will be useful when working with the UI too. — Zimano
– Zimano, Commented Jun 4, 2024 at 20:57

azelito · Accepted Answer · 2024-06-04 11:43:46Z

2

If you move the pivot (position) of the parent transform to the hinge, then you apply the localScale to the parent object you will achieve the desired result.

Example:

private float scale = 3;

And then:

transform.parent.transform.localScale = new Vector3(transform.parent.transform.localScale.x, transform.parent.transform.localScale.y, scale);

answered Jun 4, 2024 at 11:43

azelito

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1 Comment

flowerProgrammer Over a year ago

Thank you, I didn't position the parent object right

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