Suggestion: Refactor MeshToonMaterial

As suggested in https://github.com/mrdoob/three.js/pull/15105#issuecomment-453540970.

I have never seen a toon shader that supports hotspots, environment maps, or even maps for that matter… Or multiple lights.

A toon shader can be written in a few lines of code, and should not have extended Phong, which is way too flexible. I would have implemented it like MeshMatcapMaterial.

Alternative opinions, welcome.

[takahirox]

About specular, the reason why I implemented so was from MMD default shader. Like her sleeve in the first picture in the link https://ascii.jp/elem/000/000/714/714544/index-2.html MMD specular is soft edge.

I personally want to remain the soft edge for MMD but I can understand it isn’t standard. So I don’t block changing. Instead if we change I’ll think of customizing shader for MMD with Node-based material (when it’s available in core), .onBeforeCompile(), or ShaderMaterial.

As #19609 I am going to implement MMD specific material in MMDLoader, so we no longer need to take care MMD for refactoring Toon material.

[gkjohnson]

I’m all for rethinking the toon shader but can you elaborate on this a bit more?

I have never seen a toon shader that supports hotspots, environment maps, or even maps for that matter… Or multiple lights.

My understanding is that a toon shader is basically just mapping a color ramp to light intensity so it would seem that that should enable support for specular highlights through the stepped shading (though maybe not in the way they’re represented right now). The Octane and Arnold toon material docs both reference rendering specular highlights with the toon material, for example. Regarding maps the Octane docs give examples of using a roughness map to augment the shape of the color bands and something like a normal map should have the same effect.

I can’t find anything explicitly showing a toon material rendering with multiple lights (other than the final image in the Octane docs that shows two highlights) but this seems like a stylistic choice. I’m not sure if THREE allows a way to limit or choose which lights a material renders with but that would be a nice option. This write up on Zelda Wind Waker discusses how lighting changes dynamically based on closest light source, but maybe that’s considered to use case specific.