How to get a normals of certain instance of instancedMesh

Questions
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1

In my app i need to reflect some objects around target object. Because this objects identical, and for performance reason also, i use the instancedMesh object.
For perform reflection I scaled the matrix of a certain instance along some axis by -1,but as a result its normals were flipped.

Is it possible to access the normal attribute of this instance or flip the normals in another way?

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2

Extract the normal matrix from the instance matrix, and then apply it to a copy of the geometry’s vertex normals:

const normal = geometry.attributes.normal.clone();

const normalMatrix = new Matrix3().getNormalMatrix( instanceMatrix );

normal.applyNormalMatrix( normalMatrix );

As found in BufferGeometry#applyMatrix4.

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3

Thanks for the answer.
Unfortunately, this doesn’t work for me. Modified normals apply to all instances, not specific ones.

4

Unfortunately, this doesn’t work for me. Modified normals apply to all instances, not specific ones.

Perhaps I don’t understand what you are looking for in that case. All instances share the same geometry, including vertex normals. Only the instance matrix (position, rotation, scale) differs between instances.

5

I wanted to change the normals of one specific instance, not all. But I already realized that this is not possible

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