app: Splatmap support in engine

[GaladWarder]

We have a few different assets using splatmaps to increase texture density and avoid lower resolution textures, but currently there doesn't seem to be support for them in engine - the splatmap itself shows up rather than the textures.

We either need to get splatmap support into the engine, or we will need to bake down the texture which will result in the lower resolution issues we started with.

We could also try baking down to a 16k texture and crunching with KTX2, but I don't think that is the most elegant solution.

[avaer]

This makes sense to me, though I don't see any standard for splatmaps.

So we need a description of how the GLB export should work for artists so we can hook this into the shader.

Also, I think we should be doing 16k KTX2 textures regardless!

[lalalune]

we can tackle this if:

1. need an example test asset attached to the issue
2. screenshot of expected behavior (in blender or elsewhere)
3. examples of how this is handled in other engines (especially unity, babylon or unreal)

[NotFuji]

Expected behavior in Blender

In Webaverse

Material Setup

Unreal Implementation https://www.youtube.com/watch?v=tMwhg8yblGo

Test Asset: https://drive.google.com/drive/folders/1Yn1jqgdppQ6WcNF26POLT7OCEDts3Gcd

[memelotsqui]

This might be a good start, will give it a try when Im done with my current assignments :)

https://stackoverflow.com/questions/18880715/texture-splatting-with-three-js