BufferGeometryUtils.mergeVertices: Shift the hash bin to avoid missing neighbors

[gkjohnson]

Fixed #24621

Description

Adjusts the hashing approach for mergeVertice to shift the hash bin boundary away from round numbers where vertices will more commonly be. This is not a perfect fix - I think that would require a significantly slower solution - but should improve the ability to merge in more common cases.

Here's version of the codesandbox from #24621 using the new function showing that it fixes the missed vertex in this case.

https://jsfiddle.net/zejt0Lrb/

Before / After

cc @erasta @donmccurdy

[donmccurdy]

Thanks @gkjohnson! This sounds good to me.

The glTF Transform implementation has evolved since I shared it in the last thread, and now uses a spatial grid and customizable per-attribute tolerance, if anyone needs those features or wants to merge vertices offline.

https://github.com/donmccurdy/glTF-Transform/blob/68ce0f09cd96fe966a8bf2eda1e8dd5ea60137d9/packages/functions/src/weld.ts

That approach is, indeed, slower. 😄