LightingGlsl

Engine-wide lighting model shared by every lit fragment shader: albedo * (hemisphericAmbient + sceneDiffuse * lambert * sunVisibility).

The sun-visibility factor (cascade shadows) attenuates only the direct term; the ambient term is shadow-independent. A fully shadowed lit face and a sun-averted face both converge to the ambient brightness instead of multiplying two independent darkening floors - which is what used to read as "double shading" on meshes.

Ambient is hemispheric: up-facing surfaces receive more sky light than down-facing ones (mix(sceneAmbientDown, sceneAmbientUp, dot(N, up) * 0.5 + 0.5)), averaging the former flat 0.35. Callers pass upFactor precomputed in whatever space their lighting normal lives in (0.5 when no usable normal).