72 lines
2.3 KiB
C++
72 lines
2.3 KiB
C++
#include "vf/RandomTick.h"
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#include "vf/Chunk.h"
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namespace vf {
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namespace {
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uint64_t mix64(uint64_t x) {
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x += 0x9e3779b97f4a7c15ull;
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x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9ull;
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x = (x ^ (x >> 27)) * 0x94d049bb133111ebull;
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return x ^ (x >> 31);
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}
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uint64_t fold(uint64_t acc, uint64_t value) {
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return mix64(acc ^ (mix64(value) + 0x9e3779b97f4a7c15ull + (acc << 6) + (acc >> 2)));
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}
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uint64_t asBits(int v) {
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return static_cast<uint64_t>(static_cast<uint32_t>(v));
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}
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} // namespace
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RandomTick::RandomTick(uint32_t worldSeed, int ticksPerChunk)
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: seed(worldSeed), ticks(ticksPerChunk < 0 ? 0 : ticksPerChunk) {}
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uint64_t RandomTick::hash(const Vec3i& chunkCoord, long long tick, uint32_t index) const {
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uint64_t h = mix64(static_cast<uint64_t>(seed) + 0x100000001b3ull);
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h = fold(h, asBits(chunkCoord.x));
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h = fold(h, asBits(chunkCoord.y));
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h = fold(h, asBits(chunkCoord.z));
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h = fold(h, static_cast<uint64_t>(tick));
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h = fold(h, static_cast<uint64_t>(index));
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return h;
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}
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void RandomTick::sampleLocal(const Vec3i& chunkCoord, long long tick, std::vector<Vec3i>& out) const {
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out.clear();
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out.reserve(static_cast<std::size_t>(ticks));
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for (int i = 0; i < ticks; ++i) {
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uint64_t h = hash(chunkCoord, tick, static_cast<uint32_t>(i));
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int x = static_cast<int>((h & 0xffffull) % static_cast<uint64_t>(chunkSize));
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int y = static_cast<int>(((h >> 21) & 0xffffull) % static_cast<uint64_t>(chunkSize));
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int z = static_cast<int>(((h >> 42) & 0xffffull) % static_cast<uint64_t>(chunkSize));
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out.push_back(Vec3i{x, y, z});
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}
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}
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std::vector<Vec3i> RandomTick::sampleLocal(const Vec3i& chunkCoord, long long tick) const {
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std::vector<Vec3i> out;
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sampleLocal(chunkCoord, tick, out);
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return out;
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}
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void RandomTick::sampleGlobal(const Vec3i& chunkCoord, long long tick, std::vector<Vec3i>& out) const {
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sampleLocal(chunkCoord, tick, out);
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for (Vec3i& cell : out) {
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cell.x += chunkCoord.x * chunkSize;
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cell.y += chunkCoord.y * chunkSize;
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cell.z += chunkCoord.z * chunkSize;
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}
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}
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std::vector<Vec3i> RandomTick::sampleGlobal(const Vec3i& chunkCoord, long long tick) const {
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std::vector<Vec3i> out;
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sampleGlobal(chunkCoord, tick, out);
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return out;
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}
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} // namespace vf
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