labs/lsg: align CPU skin cell hashing with GLSL

Author: VrUaCom

labs/lsg/include/rengine/lsg/deterministic_hash.hpp

@@ -12,6 +12,24 @@ namespace rengine::lsg {
   return static_cast<std::uint32_t>(seed) ^ static_cast<std::uint32_t>(seed >> 32u);
 }
 
+[[nodiscard]] constexpr std::uint32_t hash_cell3_32(std::uint32_t seed_key,
+                                                    std::int32_t x,
+                                                    std::int32_t y,
+                                                    std::int32_t z) noexcept {
+  std::uint32_t h = pcg_hash(seed_key);
+  h = pcg_hash(h ^ static_cast<std::uint32_t>(x));
+  h = pcg_hash(h ^ static_cast<std::uint32_t>(y));
+  h = pcg_hash(h ^ static_cast<std::uint32_t>(z));
+  return h;
+}
+
+[[nodiscard]] constexpr std::uint32_t hash_cell3(std::uint64_t seed,
+                                                 std::int32_t x,
+                                                 std::int32_t y,
+                                                 std::int32_t z) noexcept {
+  return hash_cell3_32(fold_seed64(seed), x, y, z);
+}
+
 [[nodiscard]] constexpr std::uint32_t hash5_32(std::uint32_t seed_key, std::uint32_t region,
                                                std::int32_t x, std::int32_t y, std::int32_t z) noexcept {
   std::uint32_t h = pcg_hash(seed_key);

labs/lsg/src/surface.cpp

@@ -46,7 +46,7 @@ float value_noise(std::uint64_t seed, Vec3 p) noexcept {
   const float fy = smooth01(p.y - std::floor(p.y));
   const float fz = smooth01(p.z - std::floor(p.z));
   const auto sample = [&](std::int32_t dx, std::int32_t dy, std::int32_t dz) noexcept {
-    return hash01(hash5(seed, 0u, x0 + dx, y0 + dy, z0 + dz));
+    return hash01(hash_cell3(seed, x0 + dx, y0 + dy, z0 + dz));
   };
 
   const float v000 = sample(0, 0, 0), v100 = sample(1, 0, 0);
@@ -74,7 +74,7 @@ PoreFieldSample sample_pore_field(const CharacterGenomeV0& genome, Vec3 p,
     for (std::int32_t dy = -1; dy <= 1; ++dy) {
       for (std::int32_t dx = -1; dx <= 1; ++dx) {
         const auto cx = bx + dx, cy = by + dy, cz = bz + dz;
-        const std::uint32_t h = hash5(genome.surface_seed ^ 0xB5297A4Dull, 0u, cx, cy, cz);
+        const std::uint32_t h = hash_cell3(genome.surface_seed ^ 0xB5297A4Dull, cx, cy, cz);
         if (hash01(pcg_hash(h ^ 0xD1B54A35u)) >= density) continue;
 
         const float jx = 0.15f + 0.70f * hash01(pcg_hash(h ^ 0x68E31DA4u));

labs/lsg/tests/lsg_tests.cpp

@@ -149,6 +149,14 @@ int main() {
   static_assert(h1 == h2); static_assert(h1 != h3);
   static_assert(hash5(0x1122334455667788ull, 4, -2, 7, 11) ==
                 hash5_32(fold_seed64(0x1122334455667788ull), 4, -2, 7, 11));
+  constexpr std::uint64_t cell_seed = 0x1122334455667788ull;
+  constexpr std::uint32_t cell_key = fold_seed64(cell_seed);
+  constexpr std::uint32_t cell_manual =
+      pcg_hash(pcg_hash(pcg_hash(pcg_hash(cell_key) ^ static_cast<std::uint32_t>(-2)) ^
+                                static_cast<std::uint32_t>(7)) ^
+                         static_cast<std::uint32_t>(11));
+  static_assert(hash_cell3(cell_seed, -2, 7, 11) == cell_manual);
+  static_assert(hash_cell3_32(cell_key, -2, 7, 11) == cell_manual);
   assert(select_detail_band(4.0f) == DetailBand::macro_only); assert(select_detail_band(2.0f) == DetailBand::meso);
   assert(select_detail_band(0.5f) == DetailBand::micro); assert(select_detail_band(0.05f) == DetailBand::micro_high);