Examine light across a surface.
A compact lighting model separates diffuse and specular response. It is an explanatory instrument, not a physically complete renderer.
Roughness broadens and softens the highlight. Metalness moves more of the base colour into the specular response.
The demonstration uses a compact analytical approximation for legibility and speed. It omits image-based lighting, geometry occlusion and spectral effects.
A production material system should be verified with the target renderer, tone mapping, assets, displays and performance budget.
Technical basis: Khronos glTF material model ↗ MDN Canvas API ↗