54 lines
2.3 KiB
WebGPU Shading Language
54 lines
2.3 KiB
WebGPU Shading Language
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// RTStress closest-hit (runs in SHADE). Computes flat-shaded Lambert from
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// the hit triangle's geometric normal, accumulates ambient, and — if the
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// surface faces the sun — emits a shadow ray toward the sun. The shadow
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// ray's miss (sun visible) adds the direct term; its hit (occluded) adds
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// nothing because RT_FLAG_SKIP_CLOSEST_HIT suppresses closesthit on hit.
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//
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// Payload declared here so the assembler sees it before wfPayload / SHADE.
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struct Payload {
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color: vec3<f32>, // shadow ray: pending direct contribution
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shadowRay: u32, // 0 primary, 1 shadow
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};
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const SUN_DIR_TO_LIGHT: vec3<f32> = vec3<f32>(0.40, 0.85, 0.35);
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const SUN_COLOR: vec3<f32> = vec3<f32>(1.15, 1.05, 0.90);
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const AMBIENT_COLOR: vec3<f32> = vec3<f32>(0.12, 0.13, 0.18);
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// Cheap per-instance albedo so the grid reads as distinct cubes (and any
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// TLAS flicker as instance count scales is obvious).
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fn instanceAlbedo(i: u32) -> vec3<f32> {
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let h = i * 2654435761u;
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return vec3<f32>(
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0.35 + 0.6 * f32((h >> 0u) & 255u) / 255.0,
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0.35 + 0.6 * f32((h >> 8u) & 255u) / 255.0,
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0.35 + 0.6 * f32((h >> 16u) & 255u) / 255.0);
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}
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fn closesthit_main(ray: RayDesc, hit: HitInfo, payload: ptr<function, Payload>) {
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let meshRec = meshRecords[tlasEntries[hit.instanceId].blasMeshIdx];
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let verts = _rtFetchTri(meshRec, hit.primitiveId);
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let nObj = normalize(cross(verts[1] - verts[0], verts[2] - verts[0]));
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let nWorld = normalize(vec3<f32>(
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dot(hit.objectToWorldR0.xyz, nObj),
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dot(hit.objectToWorldR1.xyz, nObj),
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dot(hit.objectToWorldR2.xyz, nObj)));
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let albedo = instanceAlbedo(hit.customIndex);
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let worldPos = ray.origin + ray.direction * hit.t;
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let viewDir = -ray.direction;
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let nFacing = select(-nWorld, nWorld, dot(nWorld, viewDir) > 0.0);
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let sunDir = normalize(SUN_DIR_TO_LIGHT);
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let nDotL = max(0.0, dot(nFacing, sunDir));
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rtAccumulate(albedo * AMBIENT_COLOR);
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if (nDotL > 0.0) {
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var sp: Payload;
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sp.color = albedo * SUN_COLOR * nDotL;
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sp.shadowRay = 1u;
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let shadowOrigin = worldPos + nFacing * 0.05;
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rtEmitRay(shadowOrigin, 0.01, sunDir, 100000.0,
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RT_FLAG_SKIP_CLOSEST_HIT | RT_FLAG_TERMINATE_ON_FIRST_HIT,
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0xFFu, 0u, 0u, sp);
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}
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}
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