Filtering resources using 3D Tiles Next

[ptrgags]

One benefit that 3D Tiles Next brings is richer metadata that could potentially be used to filter out unneeded resources. However, we'd need to plan the API for this.

Some examples:

• When using implicit tiling, tile metadata is not always needed. It would be nice to filter by semantic, class or property name. Or perhaps allow disabling tile metadata altogether
• With multiple contents + group metadata, contents could be assigned into different groups (e.g. a terrain group and a buildings group). Then it would be helpful to filter this by group. E.g. "load only the terrain")

For implicit tiling at least, the implementation should be straightforward, the markActiveBufferViews() function in ImplicitSubtree can be modified to filter the list of buffer views. This can be used to avoid requesting unnecessary buffers.

Caveats:

• The usefulness of filtering depends on how the data is stored. If the metadata and other data (implicit tile availability, or glTF data in the case of EXT_feature_metadata) is all stored in a single binary file, there's no way to avoid downloading the whole file. Filtering would be more helpful if the optional data is stored in an external buffer.
• If we want to filter a partial buffer (e.g. to exclude some bufferViews), some of the data would have to be copied elsewhere in memory before freeing the underlying buffer.