https://www.scratchapixel.com/lessons/3d-basic-rendering/introduction-to-shading
https://www.scratchapixel.com/lessons/3d-basic-rendering/phong-shader-BRDF

https://www.clicktorelease.com/blog/creating-spherical-environment-mapping-shader/


https://alain.xyz/blog/advances-in-material-models

https://gamedev.stackexchange.com/questions/129139/how-do-i-calculate-uv-space-from-world-space-in-the-fragment-shader

// PERFECT, WORLD SPACE TEXTURES
https://forum.unity.com/threads/mapping-texture-to-world-position-instead-of-object-position.94766/

https://blog.selfshadow.com/sandbox/ltc.html square light

https://gist.github.com/galek/53557375251e1a942dfa  PBR in GLSL

//--------------------------------------
https://www.youtube.com/watch?v=TpWI2rU8iF0  TOON SHADER, multi parts. Even has shiny TOON

https://docs.blender.org/manual/en/latest/render/shader_nodes/shader/diffuse.html
https://www.learnopengles.com/tag/lambertian-reflectance/


https://threejs.org/docs/index.html#api/en/materials/MeshPhysicalMaterial
https://www.clicktorelease.com/blog/creating-spherical-environment-mapping-shader/

https://www.clicktorelease.com/code/spherical-normal-mapping/#

https://www.clicktorelease.com/code/cross-hatching/


// TOON SHADING
https://alexanderameye.github.io/simple-toon.html
https://twitter.com/csims314/status/1244391593127424002