[Feature Request] KHR_techniques_webgl

[hybridherbst]

While the KHR_techniques_webgl extension has been archived, it seems to be quite interesting to use for custom shaders embedded in gltf.
Having this as another extension here to experiment and hack with would be awesome!
Things that would probably need to be controlled by the loader:

• are the shaders assumed to be WebGL1 or WebGL2
• are they assumed ShaderMaterial or RawShaderMaterial (should the shader code be prefixed with threejs-specifics or not)

Cesium kinda "supports" this but adds a ton of custom code to the shader, probably its written for one specific exporter (https://github.com/CesiumGS/cesium/blob/94e5646e6c970a83b604652cd908064033ef9870/Source/Scene/processModelMaterialsCommon.js#L400).

If you want to tackle this I'm happy to provide sample files (either WebGL1 or WebGL2). I understand the extension hasn't been ratified because of too many unclarities (as shown by the Cesium implementation), so please close this if you feel it doesn't make sense :)

[takahirox]

Hi, thanks for the proposal.

Honestly I don't really take effort on archived extensions, but I'm willing to accept in this repository if someone makes the plugins.