How to activate parent constraint via API the same way as Activate button does?

Question

I am trying to call the same function as Activate button of the Parent Constraint component but it seems there's no such method in the API: alt text

Guess the code is hidden in the component's editor script. Was trying to achieve the same result using SetTranslationOffset and SetRotationOffset which looked pretty straight forward but ended up with objects jump a bit when the function is called:

 var positionDelta = parentConstraint.transform.position - source.position;
 var rotationDelta = Quaternion.Inverse(source.rotation) * parentConstraint.transform.rotation;
 parentConstraint.SetTranslationOffset(0, positionDelta);
 parentConstraint.SetRotationOffset(0, rotationDelta.eulerAngles);

Answer 1

Answer by Volgix · Feb 25, 2019 at 07:02 PM

So I had the same problem, and it seems like the 'jump' is due to the constraintTransform's world rotation (the bigger rotation the bigger gap).

This worked for me:

 parentConstraint.SetTranslationOffset(0, Quaternion.Inverse(constraintTransform.rotation) * positionDelta);

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spilat12 · Feb 16, 2021 at 02:02 PM 0

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I don't know WHY it works, but it works! Thanks!

Answer 2

Answer by AubreyH · May 24, 2019 at 01:53 PM

After you have added all your sources:

  //This does the equivalent of pressing the "Activate" button
         List<ConstraintSource> sources = new List<ConstraintSource>(constraint.sourceCount);
         constraint.GetSources(sources);
         
         for (int i = 0; i < sources.Count; i++)
         {
             Transform sourceTransform = sources[i].sourceTransform;
             Vector3 positionOffset = sourceTransform.InverseTransformPoint( constrainedTransform.position);
             Quaternion rotationOffset = Quaternion.Inverse(sourceTransform.rotation) * transform.rotation;
             constraint.SetTranslationOffset(i, positionOffset);
             constraint.SetRotationOffset(i, rotationOffset.eulerAngles);
         }
         
 //And remember to turn it on!
         constraint.weight = 1f;//Master weight
        
         constraint.constraintActive = true;

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tetto_green · Jun 15, 2020 at 05:30 PM 1

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Actually Vlogix's answer solves the jump issue. Unity Team, how about adding examples to Parent Constraint API after 3 years of feature existence?:)

Answer 3

Answer by Defrag · Apr 10 at 01:54 AM

Something that's not addressed by the other comments so far: If there's scaling involved, you have to explicitly ignore it when transforming for your TranslationOffset. That is:

 Matrix4x4 inverse = Matrix4x4.TRS(constraintTransform.position, constraintTransform.rotation, new Vector3(1,1,1)).inverse;
 parentConstraint.SetTranslationOffset(0, inverse.MultiplyPoint3x4(parentConstraint.transform.position));
 parentConstraint.SetRotationOffset(0, (Quaternion.Inverse(constraintTransform.rotation) * parentConstraint.transform.rotation).eulerAngles);

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How to activate parent constraint via API the same way as Activate button does?

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