[geometry-merger] Use BufferGeometryUtils.mergeBufferGeometries()

[donmccurdy]

three.js r91 will have a utility for merging buffer geometries non-destructively:

var mergedGeom = BufferGeometryUtils.mergeBufferGeometries( [ geom1, geom2, geom3 ] );

The method will return null and do nothing if any of the geometries are incompatible (different attributes, some indexed others not, etc.) so this works best with geometry that has all been created in the same way.

mrdoob/three.js#13241

[ngokevin]

done

[ngokevin]

I think I use a modified one that checks if that extra/userData object exists...been a bit of pain to have a version that works with multiple versions of three.js. That can be upstreamed to three.js to be backwards-compat

[donmccurdy]

@ngokevin the docs page still says:

Doesn't support buffer geometries yet.

Looks like that needs to be updated? With Geometry pretty much deprecated in three.js, it may be worth encouraging people that way.