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WebGPU RT: port Sponza to wavefront (shadow ray in SHADE)

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Restructure Sponza for the wavefront model: raygen emits the primary ray;
closesthit (in SHADE) gathers albedo/normal, accumulates ambient, and
emits a shadow ray carrying the pending direct term; miss adds the sky
(primary) or the direct term (shadow miss). resolve.wgsl applies the same
Reinhard+gamma the megakernel raygen did inline. User bindings moved to
group 3 (groups 0..2 reserved). RTPass maxDepth=2.

Renders the atrium correctly through the wavefront pipeline (textures,
two-sided shading, sun+ambient, shadows, tonemap).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
catbot 2026-05-31 20:16:04 +00:00
commit 376e66aeed
6 changed files with 70 additions and 134 deletions
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73
examples/Sponza/closesthit.wgsl
View file

@ -1,35 +1,25 @@
// Payload declared here so the WGSL assembler sees it before raygen
// (the assembler concatenates closesthit/anyhit/miss BEFORE raygen).
// Sponza closest-hit (runs in SHADE). In the wavefront model the lighting
// + shadow trace that used to live in raygen happens here: gather surface
// data, accumulate ambient, and emit a shadow ray toward the sun carrying
// the pending direct contribution. The shadow ray's miss adds that
// contribution (sun visible); its hit adds nothing (occluded), since
// RT_FLAG_SKIP_CLOSEST_HIT suppresses closesthit on the shadow ray.
//
// WGSL forbids cycles in the function call graph, so closesthit_main
// CAN'T call traceRay (that would create closesthit → traceRay →
// runClosestHit → closesthit). The lighting + shadow trace therefore
// happens in raygen; closesthit's job is just to gather surface data
// into the payload.
//
// shadowRay = 0 (primary): closesthit fills albedo/worldPos/normal/hit.
// shadowRay = 1 (shadow): closesthit is skipped (RT_FLAG_SKIP_CLOSEST_HIT),
// miss flips color to white = "lit".
// Payload declared here so the assembler sees it before wfPayload / SHADE.
struct Payload {
color: vec3<f32>,
shadowRay: u32,
worldPos: vec3<f32>,
hit: u32,
worldNormal: vec3<f32>,
_pad: f32,
color: vec3<f32>, // shadow ray: pending albedo·sun·nDotL
shadowRay: u32, // 0 primary, 1 shadow
};
// User-bound resources at group(2). Matches the UICustomBinding span the
// host hands to PipelineRTWebGPU::Init.
// binding 0 — albedo texture_2d_array, one layer per Sponza material
// binding 1 — sampler (linear clamp)
// binding 2 — camera storage buffer (read by raygen only)
@group(2) @binding(0) var albedos : texture_2d_array<f32>;
@group(2) @binding(1) var samp : sampler;
// User resources at @group(3) (0..2 are the wavefront pipeline's reserved
// groups). binding 0 albedo array, 1 sampler, 2 camera (raygen only).
@group(3) @binding(0) var albedos : texture_2d_array<f32>;
@group(3) @binding(1) var samp : sampler;
const SUN_DIR_TO_LIGHT: vec3<f32> = vec3<f32>(-0.35, 1.00, -0.20);
const SUN_COLOR: vec3<f32> = vec3<f32>( 1.10, 1.00, 0.85);
const AMBIENT_COLOR: vec3<f32> = vec3<f32>( 0.18, 0.20, 0.28);
// VertexNormalTangentUVPacked is `packed` on the outer struct but each
// inner `Vector<float, N, 4>` is SIMD-aligned to a 16-byte stride. So
// each vertex is 12 u32 words: normal at 0..2, tangent at 4..6, uv at 8..9.
const ATTRIB_STRIDE_U32: u32 = 12u;
const ATTRIB_NORMAL_OFFSET: u32 = 0u;
const ATTRIB_UV_OFFSET: u32 = 8u;
@ -52,7 +42,6 @@ fn fetchNormal(meshRec: MeshRecord, vertexIdx: u32) -> vec3<f32> {
}
fn closesthit_main(ray: RayDesc, hit: HitInfo, payload: ptr<function, Payload>) {
// Resolve hit triangle → 3 vertex indices.
let meshIdx = tlasEntries[hit.instanceId].blasMeshIdx;
let meshRec = meshRecords[meshIdx];
let baseIdx = meshRec.indexOffset + hit.primitiveId * 3u;
@ -61,19 +50,14 @@ fn closesthit_main(ray: RayDesc, hit: HitInfo, payload: ptr<function, Payload>)
let i2 = indices[baseIdx + 2u];
let bary = vec3<f32>(1.0 - hit.attribs.x - hit.attribs.y, hit.attribs.x, hit.attribs.y);
// Albedo via barycentric UV interpolation.
let uv0 = fetchUV(meshRec, i0);
let uv1 = fetchUV(meshRec, i1);
let uv2 = fetchUV(meshRec, i2);
let uv = uv0 * bary.x + uv1 * bary.y + uv2 * bary.z;
// OBJ V is bottom-up; sampler is top-down. fract for manual tiling.
let uvTiled = vec2<f32>(fract(uv.x), fract(1.0 - uv.y));
let layer = i32(hit.customIndex);
let albedo = textureSampleLevel(albedos, samp, uvTiled, layer, 0.0).rgb;
// World-space smooth shading normal. Multiply through the
// object-to-world rotation so this stays correct if a future scene
// rotates instances (Sponza itself is all identities).
let n0 = fetchNormal(meshRec, i0);
let n1 = fetchNormal(meshRec, i1);
let n2 = fetchNormal(meshRec, i2);
@ -83,8 +67,23 @@ fn closesthit_main(ray: RayDesc, hit: HitInfo, payload: ptr<function, Payload>)
dot(hit.objectToWorldR1.xyz, nObj),
dot(hit.objectToWorldR2.xyz, nObj)));
(*payload).color = albedo;
(*payload).worldPos = ray.origin + ray.direction * hit.t;
(*payload).worldNormal = nWorld;
(*payload).hit = 1u;
// Two-sided: flip the normal toward the camera (Sponza curtains have
// inconsistent winding).
let nFacing = select(-nWorld, nWorld, dot(nWorld, ray.direction) < 0.0);
let lightDir = normalize(SUN_DIR_TO_LIGHT);
let nDotL = max(0.0, dot(nFacing, lightDir));
let worldPos = ray.origin + ray.direction * hit.t;
// Ambient is unconditional; direct light is gated behind the shadow ray.
rtAccumulate(albedo * AMBIENT_COLOR);
if (nDotL > 0.0) {
let shadowOrigin = worldPos + nFacing * 0.5;
var sp: Payload;
sp.color = albedo * SUN_COLOR * nDotL;
sp.shadowRay = 1u;
rtEmitRay(shadowOrigin, 0.001, lightDir, 10000.0,
RT_FLAG_SKIP_CLOSEST_HIT | RT_FLAG_TERMINATE_ON_FIRST_HIT,
0xFFu, 0u, 0u, sp);
}
}

20
examples/Sponza/main.cpp
View file

@ -253,10 +253,11 @@ int main() {
DescriptorHeapWebGPU heap;
heap.Initialize(/*images*/ 2, /*buffers*/ 2, /*samplers*/ 2);
std::array<WebGPUShader, 3> shaders {{
std::array<WebGPUShader, 4> shaders {{
WebGPUShader(fs::path("raygen.wgsl"), "raygen_main", WebGPURTStage::Raygen),
WebGPUShader(fs::path("miss.wgsl"), "miss_main", WebGPURTStage::Miss),
WebGPUShader(fs::path("closesthit.wgsl"), "closesthit_main", WebGPURTStage::ClosestHit),
WebGPUShader(fs::path("resolve.wgsl"), "resolve_main", WebGPURTStage::Resolve),
}};
ShaderBindingTableWebGPU sbt;
sbt.Init(shaders);
@ -271,14 +272,15 @@ int main() {
{ .type = RTShaderGroupType::TrianglesHitGroup, .closestHitShader = 2 },
}};
// Three user bindings at @group(2):
// Three user bindings at @group(3) (the wavefront pipeline reserves
// groups 0..2 for WfParams / data heaps / indirect args):
// binding 0 — albedo texture_2d_array (one layer per material)
// binding 1 — sampler (linear clamp)
// binding 2 — Camera storage buffer (host-driven, updated per frame)
std::array<UICustomBinding, 3> bindings {{
{ .group = 2, .binding = 0, .kind = UICustomBindingKind::SampledTextureArray, ._pad = 0, .pushOffset = 0 },
{ .group = 2, .binding = 1, .kind = UICustomBindingKind::Sampler, ._pad = 0, .pushOffset = 0 },
{ .group = 2, .binding = 2, .kind = UICustomBindingKind::Buffer, ._pad = 0, .pushOffset = 0 },
{ .group = 3, .binding = 0, .kind = UICustomBindingKind::SampledTextureArray, ._pad = 0, .pushOffset = 0 },
{ .group = 3, .binding = 1, .kind = UICustomBindingKind::Sampler, ._pad = 0, .pushOffset = 0 },
{ .group = 3, .binding = 2, .kind = UICustomBindingKind::Buffer, ._pad = 0, .pushOffset = 0 },
}};
PipelineRTWebGPU pipeline;
@ -367,6 +369,7 @@ int main() {
RTPass rtPass(&pipeline);
rtPass.handlesPtr = userHandles.data();
rtPass.handlesCount = static_cast<std::uint32_t>(userHandles.size());
rtPass.maxDepth = 2; // primary + shadow
window.passes.push_back(&rtPass);
// ── Free camera: WASD + mouse-delta look ───────────────────────────
@ -375,9 +378,10 @@ int main() {
// height, looking +X down the long axis (bbox: X[-1921..1800],
// Y[-126..1429], Z[-1183..1105]). The user can fine-tune from there.
struct CamState {
Vector<float, 3, 4> position{ -1500.0f, 200.0f, 0.0f };
float yaw = 0.0f; // radians, around world +Y
float pitch = 0.0f; // radians, +pitch looks up
// 3/4 view from a corner aimed at the atrium centre.
Vector<float, 3, 4> position{ -1400.0f, 700.0f, -600.0f };
float yaw = 0.405f; // radians, around world +Y
float pitch = -0.317f; // radians, +pitch looks up
} cam;
Input::Map inputMap;

12
examples/Sponza/miss.wgsl
View file

@ -1,16 +1,12 @@
// Sponza miss (runs in SHADE). Primary miss → two-stop sky gradient.
// Shadow miss → the sun is unoccluded, so add the pending direct term.
fn miss_main(ray: RayDesc, payload: ptr<function, Payload>) {
if ((*payload).shadowRay == 1u) {
// Shadow ray escaped to infinity — the sun is visible from the
// origin, so the surface there should pick up full direct light.
// raygen reads color.x as the visibility coefficient.
(*payload).color = vec3<f32>(1.0);
rtAccumulate((*payload).color);
return;
}
// Primary miss: cheap two-stop sky gradient. (*payload).hit stays 0
// so raygen knows to skip the lighting path and just use this color.
let t = clamp(ray.direction.y * 0.5 + 0.5, 0.0, 1.0);
let sky = vec3<f32>(0.45, 0.65, 0.95);
let zenith = vec3<f32>(0.95, 0.85, 0.65);
(*payload).color = mix(sky, zenith, t);
rtAccumulate(mix(sky, zenith, t));
}

1
examples/Sponza/project.cpp
View file

@ -82,6 +82,7 @@ extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> a
cfg.files.emplace_back(fs::path("raygen.wgsl"));
cfg.files.emplace_back(fs::path("closesthit.wgsl"));
cfg.files.emplace_back(fs::path("miss.wgsl"));
cfg.files.emplace_back(fs::path("resolve.wgsl"));
EnableWasiBrowserRuntime(cfg);
} else {
cfg.shaders.emplace_back(fs::path("raygen.glsl"), std::string("main"), ShaderType::RayGen);

91
examples/Sponza/raygen.wgsl
View file

@ -1,12 +1,8 @@
// WebGPU raygen. Camera state comes from the host every frame via a
// storage buffer bound at @group(2) @binding(2); main.cpp drives that
// from WASD + mouse-delta through Crafter::Input.
//
// The shading + shadow trace all happens here because WGSL forbids
// recursive function call graphs — closesthit_main can't call traceRay
// (that would loop closesthit → traceRay → runClosestHit → closesthit).
// Raygen is the entry point and not called by anyone, so it can call
// traceRay twice (once primary, once shadow) without forming a cycle.
// Sponza raygen (runs in GENERATE). Emits the pixel's primary ray; all
// shading + the shadow trace now happen in SHADE (closesthit/miss). Camera
// state comes from the host each frame via a storage buffer at
// @group(3) @binding(2) (groups 0..2 are reserved by the wavefront
// pipeline). main.cpp drives it from WASD + mouse-delta.
struct Camera {
origin: vec3<f32>,
@ -18,92 +14,25 @@ struct Camera {
forward: vec3<f32>,
pad1: f32,
};
@group(2) @binding(2) var<storage, read> camera : Camera;
// Sun coming through Sponza's open roof. Y is up; this points "down and
// slightly along +X" so the light grazes the colonnades on one side.
const SUN_DIR_TO_LIGHT: vec3<f32> = vec3<f32>(-0.35, 1.00, -0.20);
const SUN_COLOR: vec3<f32> = vec3<f32>( 1.10, 1.00, 0.85);
const AMBIENT_COLOR: vec3<f32> = vec3<f32>( 0.18, 0.20, 0.28);
@group(3) @binding(2) var<storage, read> camera : Camera;
fn raygen_main(gid: vec3<u32>) {
if (gid.x >= hdr.surfaceW || gid.y >= hdr.surfaceH) { return; }
if (gid.x >= wfParams.surfaceW || gid.y >= wfParams.surfaceH) { return; }
let pixel = vec2<f32>(f32(gid.x), f32(gid.y));
let resolution = vec2<f32>(f32(hdr.surfaceW), f32(hdr.surfaceH));
let resolution = vec2<f32>(f32(wfParams.surfaceW), f32(wfParams.surfaceH));
let uv = (pixel + vec2<f32>(0.5)) / resolution;
let ndc = uv * 2.0 - vec2<f32>(1.0);
// Pinhole camera reconstructed from the host basis. ndc.x runs left-
// to-right across the screen → +right; ndc.y is top-down so we
// negate before applying +up.
let direction = normalize(
camera.right * (ndc.x * camera.aspect * camera.tanHalf) +
camera.up * (-ndc.y * camera.tanHalf) +
camera.forward);
// ── Primary ray ────────────────────────────────────────────────────
var payload: Payload;
payload.color = vec3<f32>(0.0);
payload.shadowRay = 0u;
payload.hit = 0u;
traceRay(
0u, 0u, 0xFFu,
0u, 0u, 0u,
camera.origin, 0.001,
direction, 10000.0,
&payload);
var finalColor: vec3<f32>;
if (payload.hit == 1u) {
// Closesthit filled albedo/worldPos/worldNormal. Two-sided
// shading: flip the normal toward the camera if we hit the back
// face — Sponza's curtains in particular have inconsistent
// winding, and without this half the surface would go black.
let albedo = payload.color;
let nFacing = select(-payload.worldNormal,
payload.worldNormal,
dot(payload.worldNormal, direction) < 0.0);
let lightDir = normalize(SUN_DIR_TO_LIGHT);
let nDotL = max(0.0, dot(nFacing, lightDir));
// ── Shadow ray ────────────────────────────────────────────────
// Only worth tracing if the surface faces the sun at all.
var visibility = 0.0;
if (nDotL > 0.0) {
// Normal-offset bias on Sponza's units (~3700 wide atrium)
// is hefty; 0.5 keeps the shadow ray clear of the originating
// triangle without producing visible "floating" shadows.
let shadowOrigin = payload.worldPos + nFacing * 0.5;
var shadowPayload: Payload;
shadowPayload.color = vec3<f32>(0.0); // default: blocked
shadowPayload.shadowRay = 1u;
shadowPayload.hit = 0u;
traceRay(
0u,
RT_FLAG_SKIP_CLOSEST_HIT | RT_FLAG_TERMINATE_ON_FIRST_HIT,
0xFFu,
0u, 0u, 0u,
shadowOrigin, 0.001,
lightDir, 10000.0,
&shadowPayload);
visibility = shadowPayload.color.x;
}
let lit = AMBIENT_COLOR + SUN_COLOR * (nDotL * visibility);
finalColor = albedo * lit;
} else {
// Sky color was filled by miss_main.
finalColor = payload.color;
}
// Reinhard tonemap + gamma 2.2 so sun-lit albedos don't clip and
// shadow detail stays readable.
let mapped = finalColor / (finalColor + vec3<f32>(1.0));
let gamma = pow(mapped, vec3<f32>(1.0 / 2.2));
textureStore(outImage,
vec2<i32>(i32(gid.x), i32(gid.y)),
vec4<f32>(gamma, 1.0));
rtEmitPrimaryRay(camera.origin, 0.001, direction, 10000.0,
0u, 0xFFu, 0u, 0u, payload);
}

7
examples/Sponza/resolve.wgsl Normal file
View file

@ -0,0 +1,7 @@
// Sponza RESOLVE-stage tonemap: Reinhard + gamma 2.2 over the linear
// accumulator — matches the tonemap the megakernel raygen applied inline.
fn resolve_main(coord: vec2<u32>, hdr: vec4<f32>) -> vec4<f32> {
let mapped = hdr.rgb / (hdr.rgb + vec3<f32>(1.0));
let g = pow(mapped, vec3<f32>(1.0 / 2.2));
return vec4<f32>(g, 1.0);
}