Every shape takes an optional material (ambient Ka, specular
Ks/Ns, and emissive Ke), applied to all its faces. Flat
shading is the baseline; a material scales the ambient fill, then layers a Blinn-Phong highlight
and an additive glow. Specular reads best on the WebGL and WebGPU backends (per-pixel
highlight); Canvas 2D approximates it per face.