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Solari: Specular path spread heuristic #22311

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Merged
alice-i-cecile merged 4 commits into from
Dec 30, 2025
Merged

Solari: Specular path spread heuristic #22311

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db69e9a
Solari: Specular path spread heuristic
JMS55 Dec 30, 2025
2470fb9
Fixes
JMS55 Dec 30, 2025
598e9ea
Misc
JMS55 Dec 30, 2025
22910c9
Merge branch 'main' into solari6-specular-path-spread
JMS55 Dec 30, 2025
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24 changes: 17 additions & 7 deletions crates/bevy_solari/src/realtime/specular_gi.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@
#import bevy_solari::gbuffer_utils::gpixel_resolve
#import bevy_solari::sampling::{sample_random_light, random_emissive_light_pdf, sample_ggx_vndf, ggx_vndf_pdf, power_heuristic}
#import bevy_solari::scene_bindings::{trace_ray, resolve_ray_hit_full, ResolvedRayHitFull, RAY_T_MIN, RAY_T_MAX}
#import bevy_solari::world_cache::{query_world_cache, WORLD_CACHE_CELL_LIFETIME}
#import bevy_solari::world_cache::{query_world_cache, get_cell_size, WORLD_CACHE_CELL_LIFETIME}

@group(1) @binding(0) var view_output: texture_storage_2d<rgba16float, read_write>;
@group(1) @binding(5) var<storage, read_write> gi_reservoirs_a: array<Reservoir>;
Expand All @@ -16,7 +16,7 @@ struct PushConstants { frame_index: u32, reset: u32 }
var<push_constant> constants: PushConstants;

const DIFFUSE_GI_REUSE_ROUGHNESS_THRESHOLD: f32 = 0.4;
const WORLD_CACHE_TERMINATION_ROUGHNESS_THRESHOLD: f32 = 0.4;
const TERMINATE_IN_WORLD_CACHE_THRESHOLD: f32 = 0.03;

@compute @workgroup_size(8, 8, 1)
fn specular_gi(@builtin(global_invocation_id) global_id: vec3<u32>) {
Expand All @@ -31,6 +31,7 @@ fn specular_gi(@builtin(global_invocation_id) global_id: vec3<u32>) {
}
let surface = gpixel_resolve(textureLoad(gbuffer, global_id.xy, 0), depth, global_id.xy, view.main_pass_viewport.zw, view.world_from_clip);

let wo_unnormalized = view.world_position - surface.world_position;
let wo = normalize(view.world_position - surface.world_position);

var radiance: vec3<f32>;
Expand All @@ -51,7 +52,12 @@ fn specular_gi(@builtin(global_invocation_id) global_id: vec3<u32>) {
wi = wi_tangent.x * T + wi_tangent.y * B + wi_tangent.z * N;
let pdf = ggx_vndf_pdf(wo_tangent, wi_tangent, surface.material.roughness);

radiance = trace_glossy_path(surface.world_position, wi, &rng) / pdf;
// https://d1qx31qr3h6wln.cloudfront.net/publications/mueller21realtime.pdf#subsection.3.4, equation (4)
let cos_theta = saturate(dot(wo, surface.world_normal));
var a0 = dot(wo_unnormalized, wo_unnormalized) / (4.0 * PI * cos_theta);
a0 *= TERMINATE_IN_WORLD_CACHE_THRESHOLD;

radiance = trace_glossy_path(surface.world_position, wi, pdf, a0, &rng) / pdf;
}

let brdf = evaluate_specular_brdf(surface.world_normal, wo, wi, surface.material.base_color, surface.material.metallic,
Expand All @@ -68,11 +74,12 @@ fn specular_gi(@builtin(global_invocation_id) global_id: vec3<u32>) {
#endif
}

fn trace_glossy_path(initial_ray_origin: vec3<f32>, initial_wi: vec3<f32>, rng: ptr<function, u32>) -> vec3<f32> {
fn trace_glossy_path(initial_ray_origin: vec3<f32>, initial_wi: vec3<f32>, initial_p_bounce: f32, a0: f32, rng: ptr<function, u32>) -> vec3<f32> {
var ray_origin = initial_ray_origin;
var wi = initial_wi;
var p_bounce = initial_p_bounce;
var surface_perfectly_specular = false;
var p_bounce = 0.0;
var path_spread = 0.0;

// Trace up to three bounces, getting the net throughput from them
var radiance = vec3(0.0);
Expand All @@ -99,8 +106,11 @@ fn trace_glossy_path(initial_ray_origin: vec3<f32>, initial_wi: vec3<f32>, rng:
// Should not perform NEE for mirror-like surfaces
surface_perfectly_specular = ray_hit.material.roughness <= 0.001 && ray_hit.material.metallic > 0.9999;

if ray_hit.material.roughness > WORLD_CACHE_TERMINATION_ROUGHNESS_THRESHOLD && i != 0u {
// Surface is very rough, terminate path in the world cache
// https://d1qx31qr3h6wln.cloudfront.net/publications/mueller21realtime.pdf#subsection.3.4, equation (3)
path_spread += sqrt((ray.t * ray.t) / (p_bounce * wo_tangent.z));

if path_spread * path_spread > a0 * get_cell_size(ray_hit.world_position, view.world_position) {
// Path spread is wide enough, terminate path in the world cache
let diffuse_brdf = ray_hit.material.base_color / PI;
radiance += throughput * diffuse_brdf * query_world_cache(ray_hit.world_position, ray_hit.geometric_world_normal, view.world_position, WORLD_CACHE_CELL_LIFETIME, rng);
break;
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