BufferGeometry.getAttribute get a BufferAttribute without casting?

[janne-hyoetylae-med]

BufferGeometry.getAttribute returns BufferAttribute | InterleavedBufferAttribute when using with the default generic types. But there is code in threejs that only accepts BufferAttribute and not interleaved.

For example this code in the threejs codebase itself would not compile if used as is in Typescript:
https://github.com/mrdoob/three.js/blob/9004ed1d3dacbede52c5657a1556789be10c0a77/src/objects/Mesh.js#L383

intersection.normal = Triangle.getInterpolatedAttribute( normal, a, b, c, barycoord, new Vector3() );

normal would be a BufferAttribute|InterleavedBufferAttribute obtained from BufferGeometry.attributes (same as getAttribute), but Triangle.getInterpolatedAttribute accepts only BufferAttribute.

Note that there are no if checks in threejs around the normal variable or in Triangle.getInterpolatedAttribute, so they assume/know that this must be a strict BufferAttribute in the mesh. Can we make the same work in Typescript without casting / type assertion?

[Methuselah96]

Thanks for the issue! I think Triangle.getInterpolatedAttribute can be updated to allow InterleavedBufferAttributes as well. Feel free to create a PR!