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Support decoupled shading from reservoirs #42

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Support decoupled shading from reservoirs #42

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89 changes: 63 additions & 26 deletions blade-render/code/ray-trace.wgsl
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Original file line number Diff line number Diff line change
Expand Up @@ -8,13 +8,16 @@

const PI: f32 = 3.1415926;
const MAX_RESERVOIRS: u32 = 2u;
// See "9.1 pairwise mis for robust reservoir reuse"
// See "9.1 pairwise mis for robust reservoir reuse" in
// "Correlations and Reuse for Fast and Accurate Physically Based Light Transport"
const PAIRWISE_MIS: bool = true;
// Base MIS for canonical samples. The constant isolates a critical difference between
// Bitterli's pseudocode (where it's 1) and NVidia's RTXDI implementation (where it's 0).
// With Bitterli's 1 we have MIS not respecting the prior history enough.
const BASE_CANONICAL_MIS: f32 = 0.05;
// See "DECOUPLING SHADING AND REUSE" in
// "Rearchitecting Spatiotemporal Resampling for Production"
const DECOUPLED_SHADING: bool = false;

struct MainParams {
frame_index: u32,
Expand Down Expand Up @@ -56,6 +59,7 @@ struct LiveReservoir {
selected_target_score: f32,
weight_sum: f32,
history: f32,
shaded_color: vec3<f32>
}

fn compute_target_score(radiance: vec3<f32>) -> f32 {
Expand All @@ -79,27 +83,67 @@ fn get_pixel_from_reservoir_index(index: i32, camera: CameraParams) -> vec2<i32>
fn bump_reservoir(r: ptr<function, LiveReservoir>, history: f32) {
(*r).history += history;
}
fn make_reservoir(ls: LightSample, light_index: u32, brdf: vec3<f32>) -> LiveReservoir {

fn make_reservoir_from_light_sample(ls: LightSample, light_index: u32, brdf: vec3<f32>) -> LiveReservoir {
let shaded = ls.radiance * brdf;
let target_score = compute_target_score(shaded);
var r: LiveReservoir;
r.selected_uv = ls.uv;
r.selected_light_index = light_index;
r.selected_target_score = compute_target_score(ls.radiance * brdf);
r.weight_sum = r.selected_target_score / ls.pdf;
r.selected_target_score = target_score;
r.weight_sum = target_score / ls.pdf;
r.history = 1.0;
r.shaded_color = shaded;
return r;
}

fn merge_light_sample(r: ptr<function, LiveReservoir>, ls: LightSample, light_index: u32, brdf: vec3<f32>, random: f32) -> bool {
let shaded = ls.radiance * brdf;
let target_score = compute_target_score(shaded);
if (target_score <= 0.0) {
return false;
}

let weight = target_score / ls.pdf;
(*r).weight_sum += weight;
(*r).history += 1.0;

if ((*r).weight_sum * random < weight) {
(*r).selected_light_index = light_index;
(*r).selected_uv = ls.uv;
(*r).selected_target_score = target_score;
(*r).shaded_color = shaded;
return true;
} else {
return false;
}
}

fn merge_reservoir(r: ptr<function, LiveReservoir>, other: LiveReservoir, random: f32) -> bool {
(*r).weight_sum += other.weight_sum;
(*r).history += other.history;
if ((*r).weight_sum * random < other.weight_sum) {
if (other.selected_target_score <= 0.0) {
return false;
}

let ratio = other.weight_sum / (*r).weight_sum;
if (DECOUPLED_SHADING) {
(*r).shaded_color = mix((*r).shaded_color, other.shaded_color, ratio);
}

if (random < ratio) {
(*r).selected_light_index = other.selected_light_index;
(*r).selected_uv = other.selected_uv;
(*r).selected_target_score = other.selected_target_score;
if (!DECOUPLED_SHADING) {
(*r).shaded_color = other.shaded_color;
}
return true;
} else {
return false;
}
}

fn unpack_reservoir(f: StoredReservoir, max_history: u32) -> LiveReservoir {
var r: LiveReservoir;
r.selected_light_index = f.light_index;
Expand All @@ -108,6 +152,7 @@ fn unpack_reservoir(f: StoredReservoir, max_history: u32) -> LiveReservoir {
let history = min(f.confidence, f32(max_history));
r.weight_sum = f.contribution_weight * f.target_score * history;
r.history = history;
r.shaded_color = vec3<f32>(0.0); // needs to be updated
return r;
}
fn pack_reservoir_detail(r: LiveReservoir, denom_factor: f32) -> StoredReservoir {
Expand Down Expand Up @@ -261,11 +306,10 @@ fn estimate_target_pdf_with_occlusion(surface: Surface, position: vec3<f32>, lig

if (check_ray_occluded(position, direction, debug_len)) {
return TargetPdf();
} else {
//Note: same as `evaluate_reflected_light`
let radiance = textureSampleLevel(env_map, sampler_nearest, light_uv, 0.0).xyz;
return make_target_pdf(brdf * radiance);
}
//Note: same as `evaluate_reflected_light`
let radiance = textureSampleLevel(env_map, sampler_nearest, light_uv, 0.0).xyz;
return make_target_pdf(brdf * radiance);
}

fn evaluate_sample(ls: LightSample, surface: Surface, start_pos: vec3<f32>, debug_len: f32) -> f32 {
Expand Down Expand Up @@ -331,7 +375,6 @@ fn compute_restir(surface: Surface, pixel: vec2<i32>, rng: ptr<function, RandomS
}

var canonical = LiveReservoir();
var canonical_radiance = vec3<f32>(0.0);
for (var i = 0u; i < parameters.num_environment_samples; i += 1u) {
var ls: LightSample;
if (parameters.environment_importance_sampling != 0u) {
Expand All @@ -342,10 +385,7 @@ fn compute_restir(surface: Surface, pixel: vec2<i32>, rng: ptr<function, RandomS

let brdf = evaluate_sample(ls, surface, position, debug_len);
if (brdf > 0.0) {
let other = make_reservoir(ls, 0u, vec3<f32>(brdf));
if (merge_reservoir(&canonical, other, random_gen(rng))) {
canonical_radiance = ls.radiance * brdf;
}
merge_light_sample(&canonical, ls, 0u, vec3<f32>(brdf), random_gen(rng));
} else {
bump_reservoir(&canonical, 1.0);
}
Expand Down Expand Up @@ -394,15 +434,14 @@ fn compute_restir(surface: Surface, pixel: vec2<i32>, rng: ptr<function, RandomS

// Next, evaluate the MIS of each of the samples versus the canonical one.
var reservoir = LiveReservoir();
var shaded_color = vec3<f32>(0.0);
var mis_canonical = BASE_CANONICAL_MIS;
for (var rid = 0u; rid < accepted_count; rid += 1u) {
let neighbor_index = accepted_reservoir_indices[rid];
let neighbor = prev_reservoirs[neighbor_index];

let max_history = select(parameters.spatial_tap_history, parameters.temporal_history, rid == temporal_index);
var other: LiveReservoir;
var other_color: vec3<f32>;
var other_history = other.history; //TODO
if (PAIRWISE_MIS) {
let neighbor_pixel = get_pixel_from_reservoir_index(neighbor_index, prev_camera);
let neighbor_history = min(neighbor.confidence, f32(max_history));
Expand Down Expand Up @@ -435,34 +474,32 @@ fn compute_restir(surface: Surface, pixel: vec2<i32>, rng: ptr<function, RandomS
other.selected_uv = neighbor.light_uv;
other.selected_target_score = t_neighbor_at_canonical.score;
other.weight_sum = t_neighbor_at_canonical.score * neighbor.contribution_weight * mis_neighbor.weight;
//Note: should be needed according to the paper
// other.history *= min(mis_neighbor.history, mis_sub_canonical.history);
other_color = t_neighbor_at_canonical.color;
other.shaded_color = t_neighbor_at_canonical.color;
//Note: the paper modifies
//other_history = min(mis_neighbor.history, mis_sub_canonical.history);
} else {
other = unpack_reservoir(neighbor, max_history);
other_color = evaluate_reflected_light(surface, other.selected_light_index, other.selected_uv);
other.shaded_color = evaluate_reflected_light(surface, other.selected_light_index, other.selected_uv);
}

if (other.weight_sum <= 0.0) {
bump_reservoir(&reservoir, other.history);
} else if (merge_reservoir(&reservoir, other, random_gen(rng))) {
shaded_color = other_color;
} else {
merge_reservoir(&reservoir, other, random_gen(rng));
}
}

// Finally, merge in the canonical sample
if (PAIRWISE_MIS) {
canonical.weight_sum *= mis_canonical / canonical.history;
}
if (merge_reservoir(&reservoir, canonical, random_gen(rng))) {
shaded_color = canonical_radiance;
}
merge_reservoir(&reservoir, canonical, random_gen(rng));

let effective_history = select(reservoir.history, BASE_CANONICAL_MIS + f32(accepted_count), PAIRWISE_MIS);
let stored = pack_reservoir_detail(reservoir, effective_history);
reservoirs[pixel_index] = stored;
var ro = RestirOutput();
ro.radiance = stored.contribution_weight * shaded_color;
ro.radiance = stored.contribution_weight * reservoir.shaded_color;
return ro;
}

Expand Down
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