how to do full child-parent transformation, without parenting?

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Hello,

i've searched the forums and answers for this, and even though i found some close matters i couldn't find it, and it must all be down to math/geometry. i don't want to parent a gameobject to another one, because i want to avoid compound colliders creation (how i wish there was an option to turn them off!) so i must do the rotation and position of the child manually from its parent.

 function LateUpdate(){
     transform.position = parentPiece.transform.position + localPosition;
     transform.rotation = parentPiece.transform.rotation * localRotation;
 }

but i know i'm missing a bit in the position. because when i rotate the "parent" object the child does not follow in the place it should. it changes the position/rotation locally and it's not really behaving like a child.

so what do i have to add at the position part to make it look right? any equations for this? thank you!

Answer 1

Answer by Steven-1 · Mar 05, 2013 at 12:45 PM

Well what you're doing is definately wrong, but I don't immediately know The correct calculations.

But you could just use a workaround though: Create a new empty gameobject with identical transform to the wannabe child, make this the child instead. Then in a Late Update you just set the wannabee child's transformation equal to the new emptychild. Ofcourse, that's assuming you don't want to change the child's local position/rotation.

Edit: or just use Transform.TransformPoint()

transform.position = parentPiece.transform.TransformPoint(localPosition);

http://docs.unity3d.com/Documentation/ScriptReference/Transform.TransformPoint.html

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vagos21 · Mar 05, 2013 at 03:22 PM 0

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great idea! actually i'll child the empty gameobjects to the parent and then set rotation and position of the indirect children almost like i did before

 function LateUpdate(){
     transform.position = parentGO.transform.position;
     transform.rotation = parentGO.transform.rotation;
 }

Steven-1 · Mar 05, 2013 at 04:19 PM 0

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That's exactly what I meant.

(my second solution is cleaner though)

sdgd · Dec 25, 2013 at 12:22 AM 0

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while searching for solution I came to this Q and digging more in to it I found this witch pointed me to Transform.RotateAround

anyway +1 to both Q && A

Answer 2

Answer by thedetective456 · Sep 10, 2021 at 11:58 AM

Hey, I actually found a cool gut repo few hours ago : https://github.com/pointcache/Unity-3d-Constraints

Why not use default constraints? Cause they update somewhere after animator IK and late update in a loop called "PreLateUpdate", which is a problem for Animator IK. It forces you to use the "Animation Rigging".

Not anymore, have fun!

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how to do full child-parent transformation, without parenting?

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