3MFLoader: Add support for Volumetric Implicits

[zalo]

Description

3MF files can now contain volumetric implicits defined as operation execution graphs.

The 3MF consortium has released a 3D Modeller for generating .3mf’s with them, similar to nTopology:
https:/3MFConsortium/gladius

This presents an opportunity to make SDF Implicits a first or second-class feature of 3D on the web!

Solution

My proposal would be to bake the execution graphs out to TSL, where a raymarching shader can evaluate them at runtime.

Alternatives

Eventually, a WebGPU Marching Cubes compute shader can take them the rest of the way into mesh-land. 🧐

Additional context

Perhaps PhysicalSDFMaterial can become a default engine material? I imagine they might ingest a TSL graph describing the SDF value and the PBR Rendering properties (diffuse color, normal, specular etc.) given a point in space; enabling it to benefit from improvements made to the main PBRMaterial! By default, they might just sample from a volumetric texture instead of evaluating the implicit programmatically.

Engine integration provides the interface for standardized cross-system interaction, like possibly with physics engines.

[zalo]

I have the roughest beginnings of a node parser implementation here: zalo@e279087
Once the ops are being read out appropriately, it will be time to hook them up to the equivalent TSL functions...

[zalo]

It occurs to me that I'm in over my head a bit ( zalo@dcabebf )... perhaps it makes more sense to add just a implicitfunction parser first, and then save the TSL transpilation for a separate PR, once I actually learn about how TSL works...

Does TSL even exist in non-webgpu version of three.js?

[Makio64]

@zalo It's confusing but the WebGPURenderer actually have two Backend : WebGL & WebGPU.
It's more like a Threejs v2 with a new core, and new concepts of Nodes & TSL : a system made to work on both technology seemlesssly.

[Mugen87]

@zalo I recommend to keep TSL generation out of 3FMLoader and return a JSON representation of the volumetric implicits instead (maybe in the userData property of the returned group). In the next step, you can create a separate library that takes the JSON representation and creates node materials from it.

In this way, 3FMLoader can easier be used with both WebGLRenderer and WebGPURenderer. Once WebGLRenderer is deprecated, a deeper integration can be considered.

[zalo]

Gotcha; since TSL isn't guaranteed to be present; it doesn't seem to make sense to compile to it in a default lib.

I'll keep the exposed implicitfunction structure simple, but optimized for others (who know more about TSL or some other language 😅 ) to step through and write a node -> node compiler.

I also have it on good authority that the javascript reference implementation for 3mf parsing will include volumetrics support soon, so the third-party ecosystem should have solutions soon regardless.