274 lines
11 KiB
C++
274 lines
11 KiB
C++
/*
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Crafter®.Graphics
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Copyright (C) 2026 Catcrafts®
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catcrafts.net
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*/
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// DOM-mode Mesh implementation: SAH BVH2 built on the host, then
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// forwarded to the JS bridge which appends the four data streams
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// (vertices, indices, BVH nodes, primRemap) into the global RT mesh
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// heaps. The handle returned by wgpuRegisterMeshBLAS goes into
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// RTInstance::accelerationStructureReference and lets the TLAS-build
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// compute pass and the traversal kernel find the BLAS data later.
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//
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// BVH layout must stay binary-identical to the WGSL `BVHNode` struct
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// declared in additional/dom-webgpu.js (rtWgslPrelude).
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module;
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module Crafter.Graphics:Mesh_implWebGPU;
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import :Mesh;
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import :WebGPU;
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import Crafter.Asset;
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import Crafter.Math;
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import std;
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using namespace Crafter;
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namespace {
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// ─── BVH builder (binned SAH, 8 bins, BVH2) ────────────────────────
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constexpr std::uint32_t kBinCount = 8;
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constexpr std::uint32_t kMaxLeafSize = 4;
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constexpr float kTraversalCost = 1.0f;
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constexpr float kIntersectCost = 1.0f;
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struct AABB {
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float lo[3] { std::numeric_limits<float>::infinity(),
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std::numeric_limits<float>::infinity(),
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std::numeric_limits<float>::infinity() };
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float hi[3] {-std::numeric_limits<float>::infinity(),
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-std::numeric_limits<float>::infinity(),
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-std::numeric_limits<float>::infinity() };
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void Extend(const float p[3]) noexcept {
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for (int a = 0; a < 3; ++a) {
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if (p[a] < lo[a]) lo[a] = p[a];
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if (p[a] > hi[a]) hi[a] = p[a];
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}
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}
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void Extend(const AABB& o) noexcept {
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for (int a = 0; a < 3; ++a) {
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if (o.lo[a] < lo[a]) lo[a] = o.lo[a];
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if (o.hi[a] > hi[a]) hi[a] = o.hi[a];
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}
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}
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float SurfaceArea() const noexcept {
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float dx = hi[0] - lo[0];
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float dy = hi[1] - lo[1];
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float dz = hi[2] - lo[2];
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if (dx < 0.0f || dy < 0.0f || dz < 0.0f) return 0.0f;
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return 2.0f * (dx*dy + dx*dz + dy*dz);
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}
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};
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struct PrimRef {
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AABB box;
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float centroid[3];
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std::uint32_t triIndex;
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};
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struct Bin {
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AABB box;
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std::uint32_t count = 0;
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};
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struct Builder {
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std::vector<PrimRef> prims;
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std::vector<BVHNode> nodes;
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std::pair<std::uint32_t, std::uint32_t> AllocateChildren() {
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std::uint32_t l = static_cast<std::uint32_t>(nodes.size());
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nodes.emplace_back();
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nodes.emplace_back();
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return { l, l + 1 };
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}
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void BuildRecursive(std::uint32_t nodeIdx,
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std::uint32_t first,
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std::uint32_t count) {
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AABB bounds, centroidBounds;
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for (std::uint32_t i = 0; i < count; ++i) {
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const auto& p = prims[first + i];
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bounds.Extend(p.box);
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centroidBounds.Extend(p.centroid);
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}
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auto emitLeaf = [&] {
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BVHNode& n = nodes[nodeIdx];
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std::memcpy(n.aabbMin, bounds.lo, sizeof(bounds.lo));
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std::memcpy(n.aabbMax, bounds.hi, sizeof(bounds.hi));
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n.firstChildOrPrim = first;
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n.primCount = count;
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};
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if (count <= kMaxLeafSize) { emitLeaf(); return; }
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int bestAxis = -1;
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float bestCost = std::numeric_limits<float>::infinity();
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std::uint32_t bestBin = 0;
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float parentArea = bounds.SurfaceArea();
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if (parentArea <= 0.0f) { emitLeaf(); return; }
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for (int axis = 0; axis < 3; ++axis) {
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float extent = centroidBounds.hi[axis] - centroidBounds.lo[axis];
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if (extent <= 0.0f) continue;
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float invExtent = static_cast<float>(kBinCount) / extent;
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std::array<Bin, kBinCount> bins{};
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for (std::uint32_t i = 0; i < count; ++i) {
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const auto& p = prims[first + i];
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float t = (p.centroid[axis] - centroidBounds.lo[axis]) * invExtent;
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std::uint32_t b = static_cast<std::uint32_t>(t);
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if (b >= kBinCount) b = kBinCount - 1;
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bins[b].box.Extend(p.box);
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bins[b].count += 1;
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}
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std::array<AABB, kBinCount - 1> leftBox;
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std::array<std::uint32_t,kBinCount - 1> leftCount{};
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{
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AABB acc; std::uint32_t cnt = 0;
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for (std::uint32_t i = 0; i < kBinCount - 1; ++i) {
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acc.Extend(bins[i].box);
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cnt += bins[i].count;
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leftBox[i] = acc;
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leftCount[i] = cnt;
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}
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}
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{
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AABB acc; std::uint32_t cnt = 0;
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for (std::int32_t i = kBinCount - 1; i >= 1; --i) {
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acc.Extend(bins[i].box);
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cnt += bins[i].count;
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std::uint32_t split = static_cast<std::uint32_t>(i - 1);
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if (leftCount[split] == 0 || cnt == 0) continue;
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float cost = kTraversalCost
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+ (leftBox[split].SurfaceArea() * leftCount[split]
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+ acc.SurfaceArea() * cnt) * kIntersectCost / parentArea;
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if (cost < bestCost) {
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bestCost = cost;
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bestAxis = axis;
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bestBin = split;
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}
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}
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}
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}
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float leafCost = static_cast<float>(count) * kIntersectCost;
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if (bestAxis < 0 || bestCost >= leafCost) { emitLeaf(); return; }
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float invExtent = static_cast<float>(kBinCount)
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/ (centroidBounds.hi[bestAxis] - centroidBounds.lo[bestAxis]);
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float lo = centroidBounds.lo[bestAxis];
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auto mid = std::partition(
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prims.begin() + first, prims.begin() + first + count,
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[&](const PrimRef& p) {
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float t = (p.centroid[bestAxis] - lo) * invExtent;
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std::uint32_t b = static_cast<std::uint32_t>(t);
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if (b >= kBinCount) b = kBinCount - 1;
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return b <= bestBin;
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});
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std::uint32_t leftCount =
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static_cast<std::uint32_t>(mid - (prims.begin() + first));
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if (leftCount == 0 || leftCount == count) { emitLeaf(); return; }
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auto [leftIdx, rightIdx] = AllocateChildren();
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{
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BVHNode& n = nodes[nodeIdx];
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std::memcpy(n.aabbMin, bounds.lo, sizeof(bounds.lo));
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std::memcpy(n.aabbMax, bounds.hi, sizeof(bounds.hi));
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n.firstChildOrPrim = leftIdx;
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n.primCount = 0;
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}
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BuildRecursive(leftIdx, first, leftCount);
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BuildRecursive(rightIdx, first + leftCount, count - leftCount);
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}
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void Build(std::span<const Vector<float, 3, 3>> vertices,
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std::span<const std::uint32_t> indices) {
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std::uint32_t triCount = static_cast<std::uint32_t>(indices.size()) / 3;
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prims.resize(triCount);
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for (std::uint32_t i = 0; i < triCount; ++i) {
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std::uint32_t i0 = indices[i*3 + 0];
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std::uint32_t i1 = indices[i*3 + 1];
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std::uint32_t i2 = indices[i*3 + 2];
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const auto& v0 = vertices[i0];
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const auto& v1 = vertices[i1];
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const auto& v2 = vertices[i2];
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float p0[3] { v0.v[0], v0.v[1], v0.v[2] };
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float p1[3] { v1.v[0], v1.v[1], v1.v[2] };
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float p2[3] { v2.v[0], v2.v[1], v2.v[2] };
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auto& pr = prims[i];
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pr.box.Extend(p0);
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pr.box.Extend(p1);
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pr.box.Extend(p2);
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pr.centroid[0] = (pr.box.lo[0] + pr.box.hi[0]) * 0.5f;
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pr.centroid[1] = (pr.box.lo[1] + pr.box.hi[1]) * 0.5f;
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pr.centroid[2] = (pr.box.lo[2] + pr.box.hi[2]) * 0.5f;
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pr.triIndex = i;
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}
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nodes.reserve(triCount * 2);
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nodes.emplace_back();
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BuildRecursive(0, 0, triCount);
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}
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};
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}
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namespace {
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// Shared between the positions-only and the compressed-asset Build paths.
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// attribsBytes is empty for positions-only meshes; the JS bridge skips
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// the attribs-heap append in that case.
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void BuildBVHAndRegister(Mesh& mesh,
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std::span<const Vector<float, 3, 3>> vertices,
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std::span<const std::uint32_t> indices,
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std::span<const std::byte> attribsBytes) {
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mesh.triangleCount = static_cast<std::uint32_t>(indices.size()) / 3;
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Builder builder;
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builder.Build(vertices, indices);
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std::vector<std::uint32_t> primRemap(mesh.triangleCount);
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for (std::uint32_t i = 0; i < mesh.triangleCount; ++i) {
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primRemap[i] = builder.prims[i].triIndex;
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}
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const BVHNode& root = builder.nodes[0];
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mesh.blasAddr = WebGPU::wgpuRegisterMeshBLAS(
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root.aabbMin[0], root.aabbMin[1], root.aabbMin[2],
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root.aabbMax[0], root.aabbMax[1], root.aabbMax[2],
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vertices.data(), static_cast<std::int32_t>(vertices.size()),
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indices.data(), static_cast<std::int32_t>(indices.size()),
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builder.nodes.data(), static_cast<std::int32_t>(builder.nodes.size()),
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primRemap.data(), static_cast<std::int32_t>(primRemap.size()),
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attribsBytes.data(), static_cast<std::int32_t>(attribsBytes.size()));
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}
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}
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void Mesh::Build(std::span<Vector<float, 3, 3>> vertices,
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std::span<std::uint32_t> indices,
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WebGPUCommandEncoderRef /*cmd*/) {
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BuildBVHAndRegister(*this, vertices, indices, {});
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}
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void Mesh::Build(const CompressedMeshAsset& asset,
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WebGPUCommandEncoderRef /*cmd*/) {
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std::vector<Vector<float, 3, 3>> vertices(asset.vertexCount);
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std::vector<std::uint32_t> indices(asset.indexCount);
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std::vector<std::byte> dataBytes(
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static_cast<std::size_t>(asset.dataCount) * asset.dataStride);
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// CompressedBlob always carries 3 regions for MeshAsset (the data region
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// can have decompressedSize=0). DecompressCPU validates output sizes
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// against region sizes, so the empty-data path needs the empty span.
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std::array<std::span<std::byte>, 3> outputs = {
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std::as_writable_bytes(std::span(vertices)),
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std::as_writable_bytes(std::span(indices)),
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std::span<std::byte>(dataBytes),
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};
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Compression::DecompressCPU(asset.blob,
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std::span(outputs).first(asset.blob.regions.size()));
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BuildBVHAndRegister(*this, vertices, indices, std::span(dataBytes));
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}
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