Node: NormalMatrix issues

[WestLangley]

This pattern, which appears in NormalNode and NodeBuilder, is not correct:

result = ( modelMatrix * vec4( objectNormal, 0.0 ) ).xyz;

...unless you assume the model matrix is uniformly-scaled. I don't think we can assume it is.

To fix this, see this article. The relevant three.js method is Matrix3.getNormalMatrix( matrix ).

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This pattern, on the other hand,

result = ( viewMatrix * vec4( reflectVec, 0.0 ) ).xyz;

is assumed to be OK because we assume the viewMatrix is not scaled at all.

/ping @sunag

[sunag]

What do you think about this other pattern?

result = inverseTransformDirection( transformedNormal, viewMatrix ).xyz;

[sunag]

It is to obtain the worldNormal

[WestLangley]

That is correct. See Transforming Normal Vectors with the Inverse Transformation here.