1#define_import_path bevy_pbr::lighting
2
3#import bevy_pbr::{
4    mesh_view_types::POINT_LIGHT_FLAGS_SPOT_LIGHT_Y_NEGATIVE,
5    mesh_view_bindings as view_bindings,
6}
7#import bevy_render::maths::PI
8
9const LAYER_BASE: u32 = 0;
10const LAYER_CLEARCOAT: u32 = 1;
11
12// From the Filament design doc
13// https://google.github.io/filament/Filament.html#table_symbols
14// Symbol Definition
15// v    View unit vector
16// l    Incident light unit vector
17// n    Surface normal unit vector
18// h    Half unit vector between l and v
19// f    BRDF
20// f_d    Diffuse component of a BRDF
21// f_r    Specular component of a BRDF
22// α    Roughness, remapped from using input perceptualRoughness
23// σ    Diffuse reflectance
24// Ω    Spherical domain
25// f0    Reflectance at normal incidence
26// f90    Reflectance at grazing angle
27// χ+(a)    Heaviside function (1 if a>0 and 0 otherwise)
28// nior    Index of refraction (IOR) of an interface
29// ⟨n⋅l⟩    Dot product clamped to [0..1]
30// ⟨a⟩    Saturated value (clamped to [0..1])
31
32// The Bidirectional Reflectance Distribution Function (BRDF) describes the surface response of a standard material
33// and consists of two components, the diffuse component (f_d) and the specular component (f_r):
34// f(v,l) = f_d(v,l) + f_r(v,l)
35//
36// The form of the microfacet model is the same for diffuse and specular
37// f_r(v,l) = f_d(v,l) = 1 / { |n⋅v||n⋅l| } ∫_Ω D(m,α) G(v,l,m) f_m(v,l,m) (v⋅m) (l⋅m) dm
38//
39// In which:
40// D, also called the Normal Distribution Function (NDF) models the distribution of the microfacets
41// G models the visibility (or occlusion or shadow-masking) of the microfacets
42// f_m is the microfacet BRDF and differs between specular and diffuse components
43//
44// The above integration needs to be approximated.
45
46// Input to a lighting function for a single layer (either the base layer or the
47// clearcoat layer).
48struct LayerLightingInput {
49    // The normal vector.
50    N: vec3<f32>,
51    // The reflected vector.
52    R: vec3<f32>,
53    // The normal vector ⋅ the view vector.
54    NdotV: f32,
55
56    // The perceptual roughness of the layer.
57    perceptual_roughness: f32,
58    // The roughness of the layer.
59    roughness: f32,
60}
61
62// Input to a lighting function (`point_light`, `spot_light`,
63// `directional_light`).
64struct LightingInput {
65#ifdef STANDARD_MATERIAL_CLEARCOAT
66    layers: array<LayerLightingInput, 2>,
67#else   // STANDARD_MATERIAL_CLEARCOAT
68    layers: array<LayerLightingInput, 1>,
69#endif  // STANDARD_MATERIAL_CLEARCOAT
70
71    // The world-space position.
72    P: vec3<f32>,
73    // The vector to the view.
74    V: vec3<f32>,
75
76    // The diffuse color of the material.
77    diffuse_color: vec3<f32>,
78
79    // Specular reflectance at the normal incidence angle.
80    //
81    // This should be read F₀, but due to Naga limitations we can't name it that.
82    F0_: vec3<f32>,
83    // Constants for the BRDF approximation.
84    //
85    // See `EnvBRDFApprox` in
86    // <https://www.unrealengine.com/en-US/blog/physically-based-shading-on-mobile>.
87    // What we call `F_ab` they call `AB`.
88    F_ab: vec2<f32>,
89
90#ifdef STANDARD_MATERIAL_CLEARCOAT
91    // The strength of the clearcoat layer.
92    clearcoat_strength: f32,
93#endif  // STANDARD_MATERIAL_CLEARCOAT
94
95#ifdef STANDARD_MATERIAL_ANISOTROPY
96    // The anisotropy strength, reflecting the amount of increased roughness in
97    // the tangent direction.
98    anisotropy: f32,
99    // The tangent direction for anisotropy: i.e. the direction in which
100    // roughness increases.
101    Ta: vec3<f32>,
102    // The bitangent direction, which is the cross product of the normal with
103    // the tangent direction.
104    Ba: vec3<f32>,
105#endif  // STANDARD_MATERIAL_ANISOTROPY
106}
107
108// Values derived from the `LightingInput` for both diffuse and specular lights.
109struct DerivedLightingInput {
110    // The half-vector between L, the incident light vector, and V, the view
111    // vector.
112    H: vec3<f32>,
113    // The normal vector ⋅ the incident light vector.
114    NdotL: f32,
115    // The normal vector ⋅ the half-vector.
116    NdotH: f32,
117    // The incident light vector ⋅ the half-vector.
118    LdotH: f32,
119}
120
121// distanceAttenuation is simply the square falloff of light intensity
122// combined with a smooth attenuation at the edge of the light radius
123//
124// light radius is a non-physical construct for efficiency purposes,
125// because otherwise every light affects every fragment in the scene
126fn getDistanceAttenuation(distanceSquare: f32, inverseRangeSquared: f32) -> f32 {
127    let factor = distanceSquare * inverseRangeSquared;
128    let smoothFactor = saturate(1.0 - factor * factor);
129    let attenuation = smoothFactor * smoothFactor;
130    return attenuation * 1.0 / max(distanceSquare, 0.0001);
131}
132
133// Normal distribution function (specular D)
134// Based on https://google.github.io/filament/Filament.html#citation-walter07
135
136// D_GGX(h,α) = α^2 / { π ((n⋅h)^2 (α2−1) + 1)^2 }
137
138// Simple implementation, has precision problems when using fp16 instead of fp32
139// see https://google.github.io/filament/Filament.html#listing_speculardfp16
140fn D_GGX(roughness: f32, NdotH: f32, h: vec3<f32>) -> f32 {
141    let oneMinusNdotHSquared = 1.0 - NdotH * NdotH;
142    let a = NdotH * roughness;
143    let k = roughness / (oneMinusNdotHSquared + a * a);
144    let d = k * k * (1.0 / PI);
145    return d;
146}
147
148// An approximation of the anisotropic GGX distribution function.
149//
150//                                     1
151//     D(𝐡) = ───────────────────────────────────────────────────
152//            παₜα_b((𝐡 ⋅ 𝐭)² / αₜ²) + (𝐡 ⋅ 𝐛)² / α_b² + (𝐡 ⋅ 𝐧)²)²
153//
154// * `T` = 𝐭 = the tangent direction = the direction of increased roughness.
155//
156// * `B` = 𝐛 = the bitangent direction = the direction of decreased roughness.
157//
158// * `at` = αₜ = the alpha-roughness in the tangent direction.
159//
160// * `ab` = α_b = the alpha-roughness in the bitangent direction.
161//
162// This is from the `KHR_materials_anisotropy` spec:
163// <https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_materials_anisotropy/README.md#individual-lights>
164fn D_GGX_anisotropic(at: f32, ab: f32, NdotH: f32, TdotH: f32, BdotH: f32) -> f32 {
165    let a2 = at * ab;
166    let f = vec3(ab * TdotH, at * BdotH, a2 * NdotH);
167    let w2 = a2 / dot(f, f);
168    let d = a2 * w2 * w2 * (1.0 / PI);
169    return d;
170}
171
172// Visibility function (Specular G)
173// V(v,l,a) = G(v,l,α) / { 4 (n⋅v) (n⋅l) }
174// such that f_r becomes
175// f_r(v,l) = D(h,α) V(v,l,α) F(v,h,f0)
176// where
177// V(v,l,α) = 0.5 / { n⋅l sqrt((n⋅v)^2 (1−α2) + α2) + n⋅v sqrt((n⋅l)^2 (1−α2) + α2) }
178// Note the two sqrt's, that may be slow on mobile, see https://google.github.io/filament/Filament.html#listing_approximatedspecularv
179fn V_SmithGGXCorrelated(roughness: f32, NdotV: f32, NdotL: f32) -> f32 {
180    let a2 = roughness * roughness;
181    let lambdaV = NdotL * sqrt((NdotV - a2 * NdotV) * NdotV + a2);
182    let lambdaL = NdotV * sqrt((NdotL - a2 * NdotL) * NdotL + a2);
183    let v = 0.5 / (lambdaV + lambdaL);
184    return v;
185}
186
187// The visibility function, anisotropic variant.
188fn V_GGX_anisotropic(
189    at: f32,
190    ab: f32,
191    NdotL: f32,
192    NdotV: f32,
193    BdotV: f32,
194    TdotV: f32,
195    TdotL: f32,
196    BdotL: f32,
197) -> f32 {
198    let GGX_V = NdotL * length(vec3(at * TdotV, ab * BdotV, NdotV));
199    let GGX_L = NdotV * length(vec3(at * TdotL, ab * BdotL, NdotL));
200    let v = 0.5 / (GGX_V + GGX_L);
201    return saturate(v);
202}
203
204// A simpler, but nonphysical, alternative to Smith-GGX. We use this for
205// clearcoat, per the Filament spec.
206//
207// https://google.github.io/filament/Filament.html#materialsystem/clearcoatmodel#toc4.9.1
208fn V_Kelemen(LdotH: f32) -> f32 {
209    return 0.25 / (LdotH * LdotH);
210}
211
212// Fresnel function
213// see https://google.github.io/filament/Filament.html#citation-schlick94
214// F_Schlick(v,h,f_0,f_90) = f_0 + (f_90 − f_0) (1 − v⋅h)^5
215fn F_Schlick_vec(f0: vec3<f32>, f90: f32, VdotH: f32) -> vec3<f32> {
216    // not using mix to keep the vec3 and float versions identical
217    return f0 + (f90 - f0) * pow(1.0 - VdotH, 5.0);
218}
219
220fn F_Schlick(f0: f32, f90: f32, VdotH: f32) -> f32 {
221    // not using mix to keep the vec3 and float versions identical
222    return f0 + (f90 - f0) * pow(1.0 - VdotH, 5.0);
223}
224
225fn fresnel(f0: vec3<f32>, LdotH: f32) -> vec3<f32> {
226    // f_90 suitable for ambient occlusion
227    // see https://google.github.io/filament/Filament.html#lighting/occlusion
228    let f90 = saturate(dot(f0, vec3<f32>(50.0 * 0.33)));
229    return F_Schlick_vec(f0, f90, LdotH);
230}
231
232// Given distribution, visibility, and Fresnel term, calculates the final
233// specular light.
234//
235// Multiscattering approximation:
236// <https://google.github.io/filament/Filament.html#listing_energycompensationimpl>
237fn specular_multiscatter(
238    input: ptr<function, LightingInput>,
239    D: f32,
240    V: f32,
241    F: vec3<f32>,
242    specular_intensity: f32,
243) -> vec3<f32> {
244    // Unpack.
245    let F0 = (*input).F0_;
246    let F_ab = (*input).F_ab;
247
248    var Fr = (specular_intensity * D * V) * F;
249    Fr *= 1.0 + F0 * (1.0 / F_ab.x - 1.0);
250    return Fr;
251}
252
253// Specular BRDF
254// https://google.github.io/filament/Filament.html#materialsystem/specularbrdf
255
256// N, V, and L must all be normalized.
257fn derive_lighting_input(N: vec3<f32>, V: vec3<f32>, L: vec3<f32>) -> DerivedLightingInput {
258    var input: DerivedLightingInput;
259    var H: vec3<f32> = normalize(L + V);
260    input.H = H;
261    input.NdotL = saturate(dot(N, L));
262    input.NdotH = saturate(dot(N, H));
263    input.LdotH = saturate(dot(L, H));
264    return input;
265}
266
267// Returns L in the `xyz` components and the specular intensity in the `w` component.
268fn compute_specular_layer_values_for_point_light(
269    input: ptr<function, LightingInput>,
270    layer: u32,
271    V: vec3<f32>,
272    light_to_frag: vec3<f32>,
273    light_position_radius: f32,
274) -> vec4<f32> {
275    // Unpack.
276    let R = (*input).layers[layer].R;
277    let a = (*input).layers[layer].roughness;
278
279    // Representative Point Area Lights.
280    // see http://blog.selfshadow.com/publications/s2013-shading-course/karis/s2013_pbs_epic_notes_v2.pdf p14-16
281    let centerToRay = dot(light_to_frag, R) * R - light_to_frag;
282    let closestPoint = light_to_frag + centerToRay * saturate(
283        light_position_radius * inverseSqrt(dot(centerToRay, centerToRay)));
284    let LspecLengthInverse = inverseSqrt(dot(closestPoint, closestPoint));
285    let normalizationFactor = a / saturate(a + (light_position_radius * 0.5 * LspecLengthInverse));
286    let intensity = normalizationFactor * normalizationFactor;
287
288    let L: vec3<f32> = closestPoint * LspecLengthInverse; // normalize() equivalent?
289    return vec4(L, intensity);
290}
291
292// Cook-Torrance approximation of the microfacet model integration using Fresnel law F to model f_m
293// f_r(v,l) = { D(h,α) G(v,l,α) F(v,h,f0) } / { 4 (n⋅v) (n⋅l) }
294fn specular(
295    input: ptr<function, LightingInput>,
296    derived_input: ptr<function, DerivedLightingInput>,
297    specular_intensity: f32,
298) -> vec3<f32> {
299    // Unpack.
300    let roughness = (*input).layers[LAYER_BASE].roughness;
301    let NdotV = (*input).layers[LAYER_BASE].NdotV;
302    let F0 = (*input).F0_;
303    let H = (*derived_input).H;
304    let NdotL = (*derived_input).NdotL;
305    let NdotH = (*derived_input).NdotH;
306    let LdotH = (*derived_input).LdotH;
307
308    // Calculate distribution.
309    let D = D_GGX(roughness, NdotH, H);
310    // Calculate visibility.
311    let V = V_SmithGGXCorrelated(roughness, NdotV, NdotL);
312    // Calculate the Fresnel term.
313    let F = fresnel(F0, LdotH);
314
315    // Calculate the specular light.
316    let Fr = specular_multiscatter(input, D, V, F, specular_intensity);
317    return Fr;
318}
319
320// Calculates the specular light for the clearcoat layer. Returns Fc, the
321// Fresnel term, in the first channel, and Frc, the specular clearcoat light, in
322// the second channel.
323//
324// <https://google.github.io/filament/Filament.html#listing_clearcoatbrdf>
325fn specular_clearcoat(
326    input: ptr<function, LightingInput>,
327    derived_input: ptr<function, DerivedLightingInput>,
328    clearcoat_strength: f32,
329    specular_intensity: f32,
330) -> vec2<f32> {
331    // Unpack.
332    let roughness = (*input).layers[LAYER_CLEARCOAT].roughness;
333    let H = (*derived_input).H;
334    let NdotH = (*derived_input).NdotH;
335    let LdotH = (*derived_input).LdotH;
336
337    // Calculate distribution.
338    let Dc = D_GGX(roughness, NdotH, H);
339    // Calculate visibility.
340    let Vc = V_Kelemen(LdotH);
341    // Calculate the Fresnel term.
342    let Fc = F_Schlick(0.04, 1.0, LdotH) * clearcoat_strength;
343    // Calculate the specular light.
344    let Frc = (specular_intensity * Dc * Vc) * Fc;
345    return vec2(Fc, Frc);
346}
347
348#ifdef STANDARD_MATERIAL_ANISOTROPY
349
350fn specular_anisotropy(
351    input: ptr<function, LightingInput>,
352    derived_input: ptr<function, DerivedLightingInput>,
353    L: vec3<f32>,
354    specular_intensity: f32,
355) -> vec3<f32> {
356    // Unpack.
357    let roughness = (*input).layers[LAYER_BASE].roughness;
358    let NdotV = (*input).layers[LAYER_BASE].NdotV;
359    let V = (*input).V;
360    let F0 = (*input).F0_;
361    let anisotropy = (*input).anisotropy;
362    let Ta = (*input).Ta;
363    let Ba = (*input).Ba;
364    let H = (*derived_input).H;
365    let NdotL = (*derived_input).NdotL;
366    let NdotH = (*derived_input).NdotH;
367    let LdotH = (*derived_input).LdotH;
368
369    let TdotL = dot(Ta, L);
370    let BdotL = dot(Ba, L);
371    let TdotH = dot(Ta, H);
372    let BdotH = dot(Ba, H);
373    let TdotV = dot(Ta, V);
374    let BdotV = dot(Ba, V);
375
376    let ab = roughness * roughness;
377    let at = mix(ab, 1.0, anisotropy * anisotropy);
378
379    let Da = D_GGX_anisotropic(at, ab, NdotH, TdotH, BdotH);
380    let Va = V_GGX_anisotropic(at, ab, NdotL, NdotV, BdotV, TdotV, TdotL, BdotL);
381    let Fa = fresnel(F0, LdotH);
382
383    // Calculate the specular light.
384    let Fr = specular_multiscatter(input, Da, Va, Fa, specular_intensity);
385    return Fr;
386}
387
388#endif  // STANDARD_MATERIAL_ANISOTROPY
389
390// Diffuse BRDF
391// https://google.github.io/filament/Filament.html#materialsystem/diffusebrdf
392// fd(v,l) = σ/π * 1 / { |n⋅v||n⋅l| } ∫Ω D(m,α) G(v,l,m) (v⋅m) (l⋅m) dm
393//
394// simplest approximation
395// float Fd_Lambert() {
396//     return 1.0 / PI;
397// }
398//
399// vec3 Fd = diffuseColor * Fd_Lambert();
400//
401// Disney approximation
402// See https://google.github.io/filament/Filament.html#citation-burley12
403// minimal quality difference
404fn Fd_Burley(
405    input: ptr<function, LightingInput>,
406    derived_input: ptr<function, DerivedLightingInput>,
407) -> f32 {
408    // Unpack.
409    let roughness = (*input).layers[LAYER_BASE].roughness;
410    let NdotV = (*input).layers[LAYER_BASE].NdotV;
411    let NdotL = (*derived_input).NdotL;
412    let LdotH = (*derived_input).LdotH;
413
414    let f90 = 0.5 + 2.0 * roughness * LdotH * LdotH;
415    let lightScatter = F_Schlick(1.0, f90, NdotL);
416    let viewScatter = F_Schlick(1.0, f90, NdotV);
417    return lightScatter * viewScatter * (1.0 / PI);
418}
419
420// Scale/bias approximation
421// https://www.unrealengine.com/en-US/blog/physically-based-shading-on-mobile
422// TODO: Use a LUT (more accurate)
423fn F_AB(perceptual_roughness: f32, NdotV: f32) -> vec2<f32> {
424    let c0 = vec4<f32>(-1.0, -0.0275, -0.572, 0.022);
425    let c1 = vec4<f32>(1.0, 0.0425, 1.04, -0.04);
426    let r = perceptual_roughness * c0 + c1;
427    let a004 = min(r.x * r.x, exp2(-9.28 * NdotV)) * r.x + r.y;
428    return vec2<f32>(-1.04, 1.04) * a004 + r.zw;
429}
430
431fn EnvBRDFApprox(F0: vec3<f32>, F_ab: vec2<f32>) -> vec3<f32> {
432    return F0 * F_ab.x + F_ab.y;
433}
434
435fn perceptualRoughnessToRoughness(perceptualRoughness: f32) -> f32 {
436    // clamp perceptual roughness to prevent precision problems
437    // According to Filament design 0.089 is recommended for mobile
438    // Filament uses 0.045 for non-mobile
439    let clampedPerceptualRoughness = clamp(perceptualRoughness, 0.089, 1.0);
440    return clampedPerceptualRoughness * clampedPerceptualRoughness;
441}
442
443fn point_light(
444    light_id: u32,
445    input: ptr<function, LightingInput>,
446    enable_diffuse: bool
447) -> vec3<f32> {
448    // Unpack.
449    let diffuse_color = (*input).diffuse_color;
450    let P = (*input).P;
451    let N = (*input).layers[LAYER_BASE].N;
452    let V = (*input).V;
453
454    let light = &view_bindings::clusterable_objects.data[light_id];
455    let light_to_frag = (*light).position_radius.xyz - P;
456    let L = normalize(light_to_frag);
457    let distance_square = dot(light_to_frag, light_to_frag);
458    let rangeAttenuation = getDistanceAttenuation(distance_square, (*light).color_inverse_square_range.w);
459
460    // Base layer
461
462    let specular_L_intensity = compute_specular_layer_values_for_point_light(
463        input,
464        LAYER_BASE,
465        V,
466        light_to_frag,
467        (*light).position_radius.w,
468    );
469    var specular_derived_input = derive_lighting_input(N, V, specular_L_intensity.xyz);
470
471    let specular_intensity = specular_L_intensity.w;
472
473#ifdef STANDARD_MATERIAL_ANISOTROPY
474    let specular_light = specular_anisotropy(input, &specular_derived_input, L, specular_intensity);
475#else   // STANDARD_MATERIAL_ANISOTROPY
476    let specular_light = specular(input, &specular_derived_input, specular_intensity);
477#endif  // STANDARD_MATERIAL_ANISOTROPY
478
479    // Clearcoat
480
481#ifdef STANDARD_MATERIAL_CLEARCOAT
482    // Unpack.
483    let clearcoat_N = (*input).layers[LAYER_CLEARCOAT].N;
484    let clearcoat_strength = (*input).clearcoat_strength;
485
486    // Perform specular input calculations again for the clearcoat layer. We
487    // can't reuse the above because the clearcoat normal might be different
488    // from the main layer normal.
489    let clearcoat_specular_L_intensity = compute_specular_layer_values_for_point_light(
490        input,
491        LAYER_CLEARCOAT,
492        V,
493        light_to_frag,
494        (*light).position_radius.w,
495    );
496    var clearcoat_specular_derived_input =
497        derive_lighting_input(clearcoat_N, V, clearcoat_specular_L_intensity.xyz);
498
499    // Calculate the specular light.
500    let clearcoat_specular_intensity = clearcoat_specular_L_intensity.w;
501    let Fc_Frc = specular_clearcoat(
502        input,
503        &clearcoat_specular_derived_input,
504        clearcoat_strength,
505        clearcoat_specular_intensity
506    );
507    let inv_Fc = 1.0 - Fc_Frc.r;    // Inverse Fresnel term.
508    let Frc = Fc_Frc.g;             // Clearcoat light.
509#endif  // STANDARD_MATERIAL_CLEARCOAT
510
511    // Diffuse.
512    // Comes after specular since its N⋅L is used in the lighting equation.
513    var derived_input = derive_lighting_input(N, V, L);
514    var diffuse = vec3(0.0);
515    if (enable_diffuse) {
516        diffuse = diffuse_color * Fd_Burley(input, &derived_input);
517    }
518
519    // See https://google.github.io/filament/Filament.html#mjx-eqn-pointLightLuminanceEquation
520    // Lout = f(v,l) Φ / { 4 π d^2 }⟨n⋅l⟩
521    // where
522    // f(v,l) = (f_d(v,l) + f_r(v,l)) * light_color
523    // Φ is luminous power in lumens
524    // our rangeAttenuation = 1 / d^2 multiplied with an attenuation factor for smoothing at the edge of the non-physical maximum light radius
525
526    // For a point light, luminous intensity, I, in lumens per steradian is given by:
527    // I = Φ / 4 π
528    // The derivation of this can be seen here: https://google.github.io/filament/Filament.html#mjx-eqn-pointLightLuminousPower
529
530    // NOTE: (*light).color.rgb is premultiplied with (*light).intensity / 4 π (which would be the luminous intensity) on the CPU
531
532    var color: vec3<f32>;
533#ifdef STANDARD_MATERIAL_CLEARCOAT
534    // Account for the Fresnel term from the clearcoat darkening the main layer.
535    //
536    // <https://google.github.io/filament/Filament.html#materialsystem/clearcoatmodel/integrationinthesurfaceresponse>
537    color = (diffuse + specular_light * inv_Fc) * inv_Fc + Frc;
538#else   // STANDARD_MATERIAL_CLEARCOAT
539    color = diffuse + specular_light;
540#endif  // STANDARD_MATERIAL_CLEARCOAT
541
542    return color * (*light).color_inverse_square_range.rgb *
543        (rangeAttenuation * derived_input.NdotL);
544}
545
546fn spot_light(
547    light_id: u32,
548    input: ptr<function, LightingInput>,
549    enable_diffuse: bool
550) -> vec3<f32> {
551    // reuse the point light calculations
552    let point_light = point_light(light_id, input, enable_diffuse);
553
554    let light = &view_bindings::clusterable_objects.data[light_id];
555
556    // reconstruct spot dir from x/z and y-direction flag
557    var spot_dir = vec3<f32>((*light).light_custom_data.x, 0.0, (*light).light_custom_data.y);
558    spot_dir.y = sqrt(max(0.0, 1.0 - spot_dir.x * spot_dir.x - spot_dir.z * spot_dir.z));
559    if ((*light).flags & POINT_LIGHT_FLAGS_SPOT_LIGHT_Y_NEGATIVE) != 0u {
560        spot_dir.y = -spot_dir.y;
561    }
562    let light_to_frag = (*light).position_radius.xyz - (*input).P.xyz;
563
564    // calculate attenuation based on filament formula https://google.github.io/filament/Filament.html#listing_glslpunctuallight
565    // spot_scale and spot_offset have been precomputed
566    // note we normalize here to get "l" from the filament listing. spot_dir is already normalized
567    let cd = dot(-spot_dir, normalize(light_to_frag));
568    let attenuation = saturate(cd * (*light).light_custom_data.z + (*light).light_custom_data.w);
569    let spot_attenuation = attenuation * attenuation;
570
571    return point_light * spot_attenuation;
572}
573
574fn directional_light(
575    light_id: u32,
576    input: ptr<function, LightingInput>,
577    enable_diffuse: bool
578) -> vec3<f32> {
579    // Unpack.
580    let diffuse_color = (*input).diffuse_color;
581    let NdotV = (*input).layers[LAYER_BASE].NdotV;
582    let N = (*input).layers[LAYER_BASE].N;
583    let V = (*input).V;
584    let roughness = (*input).layers[LAYER_BASE].roughness;
585
586    let light = &view_bindings::lights.directional_lights[light_id];
587
588    let L = (*light).direction_to_light.xyz;
589    var derived_input = derive_lighting_input(N, V, L);
590
591    var diffuse = vec3(0.0);
592    if (enable_diffuse) {
593        diffuse = diffuse_color * Fd_Burley(input, &derived_input);
594    }
595
596#ifdef STANDARD_MATERIAL_ANISOTROPY
597    let specular_light = specular_anisotropy(input, &derived_input, L, 1.0);
598#else   // STANDARD_MATERIAL_ANISOTROPY
599    let specular_light = specular(input, &derived_input, 1.0);
600#endif  // STANDARD_MATERIAL_ANISOTROPY
601
602#ifdef STANDARD_MATERIAL_CLEARCOAT
603    let clearcoat_N = (*input).layers[LAYER_CLEARCOAT].N;
604    let clearcoat_strength = (*input).clearcoat_strength;
605
606    // Perform specular input calculations again for the clearcoat layer. We
607    // can't reuse the above because the clearcoat normal might be different
608    // from the main layer normal.
609    var derived_clearcoat_input = derive_lighting_input(clearcoat_N, V, L);
610
611    let Fc_Frc =
612        specular_clearcoat(input, &derived_clearcoat_input, clearcoat_strength, 1.0);
613    let inv_Fc = 1.0 - Fc_Frc.r;
614    let Frc = Fc_Frc.g;
615#endif  // STANDARD_MATERIAL_CLEARCOAT
616
617    var color: vec3<f32>;
618#ifdef STANDARD_MATERIAL_CLEARCOAT
619    // Account for the Fresnel term from the clearcoat darkening the main layer.
620    //
621    // <https://google.github.io/filament/Filament.html#materialsystem/clearcoatmodel/integrationinthesurfaceresponse>
622    color = (diffuse + specular_light * inv_Fc) * inv_Fc * derived_input.NdotL +
623        Frc * derived_clearcoat_input.NdotL;
624#else   // STANDARD_MATERIAL_CLEARCOAT
625    color = (diffuse + specular_light) * derived_input.NdotL;
626#endif  // STANDARD_MATERIAL_CLEARCOAT
627
628    return color * (*light).color.rgb;
629}