DRACOLoader: Add parse() method

[donmccurdy]

The deprecated decodeDracoFile method should be removed and replaced with a parse method similar to other loaders. Currently decodeDracoFile does not propagate errors, and should do so. So probably a signature like:

dracoLoader.parse( arrayBuffer, /* options, maybe? */, onLoad, onError );

[mrdoob]

/* options, maybe? */

What options does it need?

[donmccurdy]

Currently decodeDracoFile takes attributeIDs and attributeTypes, which are only needed if you create a .drc file in a very particular way (which most Draco users don't). There were some other options (quantization, triangle fans) that I've removed in the latest refactoring. I omitted them to simplify things, and because I don't have any examples of someone using them, but I wouldn't be opposed to re-implementing them if the need arises, and if so those would require two additional options.

For users with Draco-compressed .gltf or .glb files (which I think is the large majority), none of this is necessary.

[mrdoob]

I think I would follow ImageBitmapLoader pattern.

var loader = new THREE.DracoLoader();
loader.setOptions( {} );
loader.parse( 'file.drc', onParse, onError );

[donmccurdy]

Disadvantage here is that attributeIDs and attributeTypes are likely to be different for each geometry decompressed. If each parse() call requires a new loader, then we'd need those loaders to share a pool of workers and balance tasks across them.

We could make sure the options are copied and stored for the task duration when parse is called, to support this pattern...

loader
  .setOptions( { ... } )
  .parse( buffer1, onLoad, onError )
  .setOptions( { ... } )
  .parse( buffer2, onLoad, onError );

... but I don't know if that's better or not. 🤔

[Mugen87]

Currently decodeDracoFile does not propagate errors, and should do so.

After #25390 and #27306, parse() is available and properly reports errors now. Since decodeDracoFile() is still available (with error handling now as well), do we still need the options parameter /setOptions() method?

If there is no urgent demand, I vote to close the issue.