CODEWITHSUNDEEP
c#unity-game-engine
peterHasemann
peterHasemann

Reputation: 1590

creating a pivot point by code in Unity

When creating a door script in Unity, you have to set a pivot point. You make the door being a child of this pivot point. When opening the door, the pivot point gets rotated and the door will rotate relative to it automatically.

I know you can create an empty GameObject in the editor, but I want to do it by code.

[SerializeField]
Vector3 pivotPosition; // the spawn position of the pivot point

Transform pivot;

void Start()
{
        pivot= new GameObject().transform; // create the pivot point
        pivot.position = pivotPosition; // position the pivot point
        transform.SetParent(pivot); // parenting
}

So this works fine, when having a door rotated by (0,0,0) in the inspector.

When rotating the door for example (0,-30,0) the pivot point is not placed correctly when creating it.

Pivot Creation

How can I create this pivot point correctly, having a correct placement even if the door is rotated by (x,y,z)

Upvotes: 2

Views: 7800

Answers (3)

CosmicGiant
CosmicGiant

Reputation: 6441

There are multiple possible solutions. Here are the ones I know about, in my order of preference:

  1. You can use Transform.RotateAround().
  2. You can pivot it using hierarchy, as you are doing. Rotating the "pivot" parent will give the desired effect of "rotating the child around the pivot".
  3. You can calculate the rotation around the pivot "manually":
    • How: rotation * (vector - pivot) + pivot
    • Where:
      • rotation = Quaternion representing your rotation.
      • (vector - pivot) puts your object at "origin" to apply rotation (same logic as using hierarchy method).
      • + pivot = reapplies the offset between the object and the pivot, after the rotation did it's thing.
      • Important: When applying rotations using Quaternions, the Quaternion should always be the first operand (don't do this: (vector - pivot) * rotation).
  4. If you are creating a 3D mesh, specially in a modelling application, you can simply adjust the pivot there.
    • Bonus: In this case, you can even do the open/close animations there, if your 3D application supports animation (which it probably does).
  5. You can use (Unity) animations, regardless of your 3D model's pivot.

Upvotes: 0

yes
yes

Reputation: 967

You could use Transform.RotateAround

Example

using UnityEngine;

public class RotateAround : MonoBehaviour {

    public Transform pivot;
    public float degreesPerSecond;

    void Update () {
        transform.RotateAround(pivot.position, Vector3.up, degreesPerSecond * Time.deltaTime);
    }
}

https://docs.unity3d.com/ScriptReference/Transform.RotateAround.html

Upvotes: 3

Maglethong Spirr
Maglethong Spirr

Reputation: 443

By doing pivot.position = pivotPosition; you are placing the pivot at the center of your object.

I see 3 viable options here:

1 - If you are making the model of the door, you could make its center be on the pivot's position also on the ground to help position the door's height.

2 - Use a door prefab with a parent object on the pivot's position. (Could actually use that parent as pivot instead of creating it by script)

3 - If the Door's GameObject center is in its center and you can't change it you can calculate it either manually or using MeshRenderer.bounds.

Upvotes: 1

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