Likely bug in Quaternion.copyRotationInto #324

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1. robertmuth commented on Jun 5, 2024

   

   robertmuth

   on Jun 5, 2024

   Author

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   It could be that I am merely misunderstanding the API instead of

   dir.rotate(x);

   using

   x.applyQuaternion(dir);

   seems to work.

   If that is indeed the case, maybe the documentation could be updated.

   I also have a related feature request: quaternion multiplication always forces a allocation.
   It would be nice tio have a version that multiplies into a given (empty) quaternion.
2. notakshitgoyal commented on Dec 1, 2024

   

   notakshitgoyal

   on Dec 1, 2024

   Last edited by spydon

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   void TestMe(VM.Quaternion dir) {
     print("quad: ${dir}");
     VM.Matrix3 rot = VM.Matrix3.identity();
   
     VM.Vector3 x = VM.Vector3.zero();
     x.setValues(0.0, 1.0, 0.0);
     dir.rotate(x);
     x.normalize();  // Normalize after quaternion rotation
     print("Direction from quad: ${x}");
   
     dir.copyRotationInto(rot);
     x.setValues(0.0, 1.0, 0.0);
     rot.transform(x);
     x.normalize();  // Normalize after matrix transformation
     print("Direction from rot: ${x}");
   }
3. robertmuth commented on Dec 1, 2024

   

   robertmuth

   on Dec 1, 2024

   Author

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   Could you add a little more "prose" to the answer - people that look at this in a couple of years will be thankful.

   E.g.:

   Why do you have to normalize? Is this a well known math fact? If so, provide a link.
   Or maybe this is only necessary for a certain class of Quaternions. If so, how can one tell?

   Also, what is the recommended course of action: do nothing, add the normalization step to the library, add a warning to the library documentation.
4. stuartmorgan-g commented on Jun 3, 2026

   

   stuartmorgan-g

   on Jun 3, 2026

   Contributor

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   This package has moved to https://github.com/flutter/core-packages, so if this issue is still relevant please re-file it in https://github.com/flutter/flutter. Thanks!