GLTF2Loader: Remove unused shader extension.

[donmccurdy]

Shaders were removed from the core specification with glTF2.0, and will eventually be defined through an optional extension, KHR_technique_webgl. But that spec hasn't been created yet, and there are multiple higher-priority extensions to finish first (lights, Draco, Blinn-Phong materials...). When the extension does get defined, it may very possibly be targeting WebGL 2.0.

So in the interest of maintaining and refactoring the existing loader, I'd like to remove the currently-defunct KHR_technique_webgl code. 😢 We can always resurrect it when the time is right.

This also simplifies our .clone() issues significantly.

/cc @takahirox

[takahirox]

IMO, removing and simplifying are nice if the current glTF loader shader is old spec.

[mrdoob]

Thanks!

[takahirox]

BTW what glTF spec threads should I see to follow the shader and extension priority discussion?

[donmccurdy]

@takahirox active issues in the glTF repo are a reasonably good indicator; some more urgent ones are:

• glTF 2.0: New KHR_lights extension KhronosGroup/glTF#945 (lights)
• KHR_draco_mesh_compression KhronosGroup/glTF#874 (draco compression)
• glTF 2.0: New KHR_environments extension KhronosGroup/glTF#946 (environments)
• glTF 2.0: New/modified KHR_materials_common extension KhronosGroup/glTF#947 (common materials)

The Draco team is helping with the three.js implementation for KhronosGroup/glTF#874, also.