pbr_lighting.wgsl

Input to a lighting function for a single layer (either the base layer or the clearcoat layer).

Input to a lighting function (point_light`, `spot_light, directional_light).

Values derived from the LightingInput for both diffuse and specular lights.

distanceAttenuation is simply the square falloff of light intensity combined with a smooth attenuation at the edge of the light radius light radius is a non-physical construct for efficiency purposes, because otherwise every light affects every fragment in the scene

Simple implementation, has precision problems when using fp16 instead of fp32 see https://google.github.io/filament/Filament.html#listing_speculardfp16

An approximation of the anisotropic GGX distribution function. 1 D(𝐡) = ─────────────────────────────────────────────────── παₜα_b((𝐡 ⋅ 𝐭)² / αₜ²) + (𝐡 ⋅ 𝐛)² / α_b² + (𝐡 ⋅ 𝐧)²)² * T = 𝐭 = the tangent direction = the direction of increased roughness. * B = 𝐛 = the bitangent direction = the direction of decreased roughness. * at = αₜ = the alpha-roughness in the tangent direction. * ab = α_b = the alpha-roughness in the bitangent direction. This is from the KHR_materials_anisotropy spec: <https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_materials_anisotropy/README.md#individual-lights>

Visibility function (Specular G) V(v,l,a) = G(v,l,α) / { 4 (n⋅v) (n⋅l) } such that f_r becomes f_r(v,l) = D(h,α) V(v,l,α) F(v,h,f0) where V(v,l,α) = 0.5 / { n⋅l sqrt((n⋅v)^2 (1−α2) + α2) + n⋅v sqrt((n⋅l)^2 (1−α2) + α2) } Note the two sqrt's, that may be slow on mobile, see https://google.github.io/filament/Filament.html#listing_approximatedspecularv

The visibility function, anisotropic variant.

A simpler, but nonphysical, alternative to Smith-GGX. We use this for clearcoat, per the Filament spec. https://google.github.io/filament/Filament.html#materialsystem/clearcoatmodel#toc4.9.1

Fresnel function see https://google.github.io/filament/Filament.html#citation-schlick94 F_Schlick(v,h,f_0,f_90) = f_0 + (f_90 − f_0) (1 − v⋅h)^5

Given distribution, visibility, and Fresnel term, calculates the final specular light. Multiscattering approximation: <https://google.github.io/filament/Filament.html#listing_energycompensationimpl>

N, V, and L must all be normalized.

Returns L in the xyz` components and the specular intensity in the `w component.

Cook-Torrance approximation of the microfacet model integration using Fresnel law F to model f_m f_r(v,l) = { D(h,α) G(v,l,α) F(v,h,f0) } / { 4 (n⋅v) (n⋅l) }

Calculates the specular light for the clearcoat layer. Returns Fc, the Fresnel term, in the first channel, and Frc, the specular clearcoat light, in the second channel. <https://google.github.io/filament/Filament.html#listing_clearcoatbrdf>

Diffuse BRDF https://google.github.io/filament/Filament.html#materialsystem/diffusebrdf fd(v,l) = σ/π * 1 / { |n⋅v||n⋅l| } ∫Ω D(m,α) G(v,l,m) (v⋅m) (l⋅m) dm simplest approximation float Fd_Lambert() { return 1.0 / PI; } vec3 Fd = diffuseColor * Fd_Lambert(); Disney approximation See https://google.github.io/filament/Filament.html#citation-burley12 minimal quality difference

Scale/bias approximation https://www.unrealengine.com/en-US/blog/physically-based-shading-on-mobile TODO: Use a LUT (more accurate)