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    var LtFdotR = dot(light_to_frag, R);
282
283    // HACK: the following line is an amendment to fix a discontinuity when a surface
284    // intersects the light sphere. See https://github.com/bevyengine/bevy/issues/13318
285    //
286    // This sentence in the reference is crux of the problem: "We approximate finding the point with the
287    // smallest angle to the reflection ray by finding the point with the smallest distance to the ray."
288    // This approximation turns out to be completely wrong for points inside or near the sphere.
289    // Clamping this dot product to be positive ensures `centerToRay` lies on ray and not behind it.
290    // Any non-zero epsilon works here, it just has to be positive to avoid a singularity at zero.
291    // However, this is still far from physically accurate. Deriving an exact solution would help,
292    // but really we should adopt a superior solution to area lighting, such as:
293    // Physically Based Area Lights by Michal Drobot, or
294    // Polygonal-Light Shading with Linearly Transformed Cosines by Eric Heitz et al.
295    LtFdotR = max(0.0001, LtFdotR);
296
297    let centerToRay = LtFdotR * R - light_to_frag;
298    let closestPoint = light_to_frag + centerToRay * saturate(
299        light_position_radius * inverseSqrt(dot(centerToRay, centerToRay)));
300    let LspecLengthInverse = inverseSqrt(dot(closestPoint, closestPoint));
301    let normalizationFactor = a / saturate(a + (light_position_radius * 0.5 * LspecLengthInverse));
302    let intensity = normalizationFactor * normalizationFactor;
303
304    let L: vec3<f32> = closestPoint * LspecLengthInverse; // normalize() equivalent?
305    return vec4(L, intensity);
306}
307
308// Cook-Torrance approximation of the microfacet model integration using Fresnel law F to model f_m
309// f_r(v,l) = { D(h,α) G(v,l,α) F(v,h,f0) } / { 4 (n⋅v) (n⋅l) }
310fn specular(
311    input: ptr<function, LightingInput>,
312    derived_input: ptr<function, DerivedLightingInput>,
313    specular_intensity: f32,
314) -> vec3<f32> {
315    // Unpack.
316    let roughness = (*input).layers[LAYER_BASE].roughness;
317    let NdotV = (*input).layers[LAYER_BASE].NdotV;
318    let F0 = (*input).F0_;
319    let H = (*derived_input).H;
320    let NdotL = (*derived_input).NdotL;
321    let NdotH = (*derived_input).NdotH;
322    let LdotH = (*derived_input).LdotH;
323
324    // Calculate distribution.
325    let D = D_GGX(roughness, NdotH, H);
326    // Calculate visibility.
327    let V = V_SmithGGXCorrelated(roughness, NdotV, NdotL);
328    // Calculate the Fresnel term.
329    let F = fresnel(F0, LdotH);
330
331    // Calculate the specular light.
332    let Fr = specular_multiscatter(input, D, V, F, specular_intensity);
333    return Fr;
334}
335
336// Calculates the specular light for the clearcoat layer. Returns Fc, the
337// Fresnel term, in the first channel, and Frc, the specular clearcoat light, in
338// the second channel.
339//
340// <https://google.github.io/filament/Filament.html#listing_clearcoatbrdf>
341fn specular_clearcoat(
342    input: ptr<function, LightingInput>,
343    derived_input: ptr<function, DerivedLightingInput>,
344    clearcoat_strength: f32,
345    specular_intensity: f32,
346) -> vec2<f32> {
347    // Unpack.
348    let roughness = (*input).layers[LAYER_CLEARCOAT].roughness;
349    let H = (*derived_input).H;
350    let NdotH = (*derived_input).NdotH;
351    let LdotH = (*derived_input).LdotH;
352
353    // Calculate distribution.
354    let Dc = D_GGX(roughness, NdotH, H);
355    // Calculate visibility.
356    let Vc = V_Kelemen(LdotH);
357    // Calculate the Fresnel term.
358    let Fc = F_Schlick(0.04, 1.0, LdotH) * clearcoat_strength;
359    // Calculate the specular light.
360    let Frc = (specular_intensity * Dc * Vc) * Fc;
361    return vec2(Fc, Frc);
362}
363
364#ifdef STANDARD_MATERIAL_ANISOTROPY
365
366fn specular_anisotropy(
367    input: ptr<function, LightingInput>,
368    derived_input: ptr<function, DerivedLightingInput>,
369    L: vec3<f32>,
370    specular_intensity: f32,
371) -> vec3<f32> {
372    // Unpack.
373    let roughness = (*input).layers[LAYER_BASE].roughness;
374    let NdotV = (*input).layers[LAYER_BASE].NdotV;
375    let V = (*input).V;
376    let F0 = (*input).F0_;
377    let anisotropy = (*input).anisotropy;
378    let Ta = (*input).Ta;
379    let Ba = (*input).Ba;
380    let H = (*derived_input).H;
381    let NdotL = (*derived_input).NdotL;
382    let NdotH = (*derived_input).NdotH;
383    let LdotH = (*derived_input).LdotH;
384
385    let TdotL = dot(Ta, L);
386    let BdotL = dot(Ba, L);
387    let TdotH = dot(Ta, H);
388    let BdotH = dot(Ba, H);
389    let TdotV = dot(Ta, V);
390    let BdotV = dot(Ba, V);
391
392    let ab = roughness * roughness;
393    let at = mix(ab, 1.0, anisotropy * anisotropy);
394
395    let Da = D_GGX_anisotropic(at, ab, NdotH, TdotH, BdotH);
396    let Va = V_GGX_anisotropic(at, ab, NdotL, NdotV, BdotV, TdotV, TdotL, BdotL);
397    let Fa = fresnel(F0, LdotH);
398
399    // Calculate the specular light.
400    let Fr = specular_multiscatter(input, Da, Va, Fa, specular_intensity);
401    return Fr;
402}
403
404#endif  // STANDARD_MATERIAL_ANISOTROPY
405
406// Diffuse BRDF
407// https://google.github.io/filament/Filament.html#materialsystem/diffusebrdf
408// fd(v,l) = σ/π * 1 / { |n⋅v||n⋅l| } ∫Ω D(m,α) G(v,l,m) (v⋅m) (l⋅m) dm
409//
410// simplest approximation
411// float Fd_Lambert() {
412//     return 1.0 / PI;
413// }
414//
415// vec3 Fd = diffuseColor * Fd_Lambert();
416//
417// Disney approximation
418// See https://google.github.io/filament/Filament.html#citation-burley12
419// minimal quality difference
420fn Fd_Burley(
421    input: ptr<function, LightingInput>,
422    derived_input: ptr<function, DerivedLightingInput>,
423) -> f32 {
424    // Unpack.
425    let roughness = (*input).layers[LAYER_BASE].roughness;
426    let NdotV = (*input).layers[LAYER_BASE].NdotV;
427    let NdotL = (*derived_input).NdotL;
428    let LdotH = (*derived_input).LdotH;
429
430    let f90 = 0.5 + 2.0 * roughness * LdotH * LdotH;
431    let lightScatter = F_Schlick(1.0, f90, NdotL);
432    let viewScatter = F_Schlick(1.0, f90, NdotV);
433    return lightScatter * viewScatter * (1.0 / PI);
434}
435
436// Scale/bias approximation
437// https://www.unrealengine.com/en-US/blog/physically-based-shading-on-mobile
438// TODO: Use a LUT (more accurate)
439fn F_AB(perceptual_roughness: f32, NdotV: f32) -> vec2<f32> {
440    let c0 = vec4<f32>(-1.0, -0.0275, -0.572, 0.022);
441    let c1 = vec4<f32>(1.0, 0.0425, 1.04, -0.04);
442    let r = perceptual_roughness * c0 + c1;
443    let a004 = min(r.x * r.x, exp2(-9.28 * NdotV)) * r.x + r.y;
444    return vec2<f32>(-1.04, 1.04) * a004 + r.zw;
445}
446
447fn EnvBRDFApprox(F0: vec3<f32>, F_ab: vec2<f32>) -> vec3<f32> {
448    return F0 * F_ab.x + F_ab.y;
449}
450
451fn perceptualRoughnessToRoughness(perceptualRoughness: f32) -> f32 {
452    // clamp perceptual roughness to prevent precision problems
453    // According to Filament design 0.089 is recommended for mobile
454    // Filament uses 0.045 for non-mobile
455    let clampedPerceptualRoughness = clamp(perceptualRoughness, 0.089, 1.0);
456    return clampedPerceptualRoughness * clampedPerceptualRoughness;
457}
458
459fn point_light(
460    light_id: u32,
461    input: ptr<function, LightingInput>,
462    enable_diffuse: bool
463) -> vec3<f32> {
464    // Unpack.
465    let diffuse_color = (*input).diffuse_color;
466    let P = (*input).P;
467    let N = (*input).layers[LAYER_BASE].N;
468    let V = (*input).V;
469
470    let light = &view_bindings::clusterable_objects.data[light_id];
471    let light_to_frag = (*light).position_radius.xyz - P;
472    let L = normalize(light_to_frag);
473    let distance_square = dot(light_to_frag, light_to_frag);
474    let rangeAttenuation = getDistanceAttenuation(distance_square, (*light).color_inverse_square_range.w);
475
476    // Base layer
477
478    let specular_L_intensity = compute_specular_layer_values_for_point_light(
479        input,
480        LAYER_BASE,
481        V,
482        light_to_frag,
483        (*light).position_radius.w,
484    );
485    var specular_derived_input = derive_lighting_input(N, V, specular_L_intensity.xyz);
486
487    let specular_intensity = specular_L_intensity.w;
488
489#ifdef STANDARD_MATERIAL_ANISOTROPY
490    let specular_light = specular_anisotropy(input, &specular_derived_input, L, specular_intensity);
491#else   // STANDARD_MATERIAL_ANISOTROPY
492    let specular_light = specular(input, &specular_derived_input, specular_intensity);
493#endif  // STANDARD_MATERIAL_ANISOTROPY
494
495    // Clearcoat
496
497#ifdef STANDARD_MATERIAL_CLEARCOAT
498    // Unpack.
499    let clearcoat_N = (*input).layers[LAYER_CLEARCOAT].N;
500    let clearcoat_strength = (*input).clearcoat_strength;
501
502    // Perform specular input calculations again for the clearcoat layer. We
503    // can't reuse the above because the clearcoat normal might be different
504    // from the main layer normal.
505    let clearcoat_specular_L_intensity = compute_specular_layer_values_for_point_light(
506        input,
507        LAYER_CLEARCOAT,
508        V,
509        light_to_frag,
510        (*light).position_radius.w,
511    );
512    var clearcoat_specular_derived_input =
513        derive_lighting_input(clearcoat_N, V, clearcoat_specular_L_intensity.xyz);
514
515    // Calculate the specular light.
516    let clearcoat_specular_intensity = clearcoat_specular_L_intensity.w;
517    let Fc_Frc = specular_clearcoat(
518        input,
519        &clearcoat_specular_derived_input,
520        clearcoat_strength,
521        clearcoat_specular_intensity
522    );
523    let inv_Fc = 1.0 - Fc_Frc.r;    // Inverse Fresnel term.
524    let Frc = Fc_Frc.g;             // Clearcoat light.
525#endif  // STANDARD_MATERIAL_CLEARCOAT
526
527    // Diffuse.
528    // Comes after specular since its N⋅L is used in the lighting equation.
529    var derived_input = derive_lighting_input(N, V, L);
530    var diffuse = vec3(0.0);
531    if (enable_diffuse) {
532        diffuse = diffuse_color * Fd_Burley(input, &derived_input);
533    }
534
535    // See https://google.github.io/filament/Filament.html#mjx-eqn-pointLightLuminanceEquation
536    // Lout = f(v,l) Φ / { 4 π d^2 }⟨n⋅l⟩
537    // where
538    // f(v,l) = (f_d(v,l) + f_r(v,l)) * light_color
539    // Φ is luminous power in lumens
540    // our rangeAttenuation = 1 / d^2 multiplied with an attenuation factor for smoothing at the edge of the non-physical maximum light radius
541
542    // For a point light, luminous intensity, I, in lumens per steradian is given by:
543    // I = Φ / 4 π
544    // The derivation of this can be seen here: https://google.github.io/filament/Filament.html#mjx-eqn-pointLightLuminousPower
545
546    // NOTE: (*light).color.rgb is premultiplied with (*light).intensity / 4 π (which would be the luminous intensity) on the CPU
547
548    var color: vec3<f32>;
549#ifdef STANDARD_MATERIAL_CLEARCOAT
550    // Account for the Fresnel term from the clearcoat darkening the main layer.
551    //
552    // <https://google.github.io/filament/Filament.html#materialsystem/clearcoatmodel/integrationinthesurfaceresponse>
553    color = (diffuse + specular_light * inv_Fc) * inv_Fc + Frc;
554#else   // STANDARD_MATERIAL_CLEARCOAT
555    color = diffuse + specular_light;
556#endif  // STANDARD_MATERIAL_CLEARCOAT
557
558    return color * (*light).color_inverse_square_range.rgb *
559        (rangeAttenuation * derived_input.NdotL);
560}
561
562fn spot_light(
563    light_id: u32,
564    input: ptr<function, LightingInput>,
565    enable_diffuse: bool
566) -> vec3<f32> {
567    // reuse the point light calculations
568    let point_light = point_light(light_id, input, enable_diffuse);
569
570    let light = &view_bindings::clusterable_objects.data[light_id];
571
572    // reconstruct spot dir from x/z and y-direction flag
573    var spot_dir = vec3<f32>((*light).light_custom_data.x, 0.0, (*light).light_custom_data.y);
574    spot_dir.y = sqrt(max(0.0, 1.0 - spot_dir.x * spot_dir.x - spot_dir.z * spot_dir.z));
575    if ((*light).flags & POINT_LIGHT_FLAGS_SPOT_LIGHT_Y_NEGATIVE) != 0u {
576        spot_dir.y = -spot_dir.y;
577    }
578    let light_to_frag = (*light).position_radius.xyz - (*input).P.xyz;
579
580    // calculate attenuation based on filament formula https://google.github.io/filament/Filament.html#listing_glslpunctuallight
581    // spot_scale and spot_offset have been precomputed
582    // note we normalize here to get "l" from the filament listing. spot_dir is already normalized
583    let cd = dot(-spot_dir, normalize(light_to_frag));
584    let attenuation = saturate(cd * (*light).light_custom_data.z + (*light).light_custom_data.w);
585    let spot_attenuation = attenuation * attenuation;
586
587    return point_light * spot_attenuation;
588}
589
590fn directional_light(
591    light_id: u32,
592    input: ptr<function, LightingInput>,
593    enable_diffuse: bool
594) -> vec3<f32> {
595    // Unpack.
596    let diffuse_color = (*input).diffuse_color;
597    let NdotV = (*input).layers[LAYER_BASE].NdotV;
598    let N = (*input).layers[LAYER_BASE].N;
599    let V = (*input).V;
600    let roughness = (*input).layers[LAYER_BASE].roughness;
601
602    let light = &view_bindings::lights.directional_lights[light_id];
603
604    let L = (*light).direction_to_light.xyz;
605    var derived_input = derive_lighting_input(N, V, L);
606
607    var diffuse = vec3(0.0);
608    if (enable_diffuse) {
609        diffuse = diffuse_color * Fd_Burley(input, &derived_input);
610    }
611
612#ifdef STANDARD_MATERIAL_ANISOTROPY
613    let specular_light = specular_anisotropy(input, &derived_input, L, 1.0);
614#else   // STANDARD_MATERIAL_ANISOTROPY
615    let specular_light = specular(input, &derived_input, 1.0);
616#endif  // STANDARD_MATERIAL_ANISOTROPY
617
618#ifdef STANDARD_MATERIAL_CLEARCOAT
619    let clearcoat_N = (*input).layers[LAYER_CLEARCOAT].N;
620    let clearcoat_strength = (*input).clearcoat_strength;
621
622    // Perform specular input calculations again for the clearcoat layer. We
623    // can't reuse the above because the clearcoat normal might be different
624    // from the main layer normal.
625    var derived_clearcoat_input = derive_lighting_input(clearcoat_N, V, L);
626
627    let Fc_Frc =
628        specular_clearcoat(input, &derived_clearcoat_input, clearcoat_strength, 1.0);
629    let inv_Fc = 1.0 - Fc_Frc.r;
630    let Frc = Fc_Frc.g;
631#endif  // STANDARD_MATERIAL_CLEARCOAT
632
633    var color: vec3<f32>;
634#ifdef STANDARD_MATERIAL_CLEARCOAT
635    // Account for the Fresnel term from the clearcoat darkening the main layer.
636    //
637    // <https://google.github.io/filament/Filament.html#materialsystem/clearcoatmodel/integrationinthesurfaceresponse>
638    color = (diffuse + specular_light * inv_Fc) * inv_Fc * derived_input.NdotL +
639        Frc * derived_clearcoat_input.NdotL;
640#else   // STANDARD_MATERIAL_CLEARCOAT
641    color = (diffuse + specular_light) * derived_input.NdotL;
642#endif  // STANDARD_MATERIAL_CLEARCOAT
643
644    return color * (*light).color.rgb;
645}