VoxelForge/Standalone/Source/WorldMesher.h

#pragma once

#include "OwnerWorldLoader.h"
#include "VoxelClipmapDesiredTiles.h"
#include "VoxelMarchingCubesMesher.h"

#include <atomic>
#include <chrono>
#include <thread>

struct FStandaloneCpuVertex { float Position[3]; float Normal[3]; };

struct FStandaloneCpuLevel
{
    std::vector<FStandaloneCpuVertex> Vertices;
    std::vector<uint32> Indices;
    uint64 VertexCount = 0;
    uint64 IndexCount = 0;
    uint64 TileCount = 0;
    uint64 NonEmptyTiles = 0;
    uint64 DensitySamples = 0;
    double Seconds = 0.0;
};

struct FStandaloneCpuClipmap
{
    std::array<FStandaloneCpuLevel,9> Levels;
    FIntVector CenterChunk = FIntVector::ZeroValue;
    int32 MinimumChunkZ = MIN_int32;
    int32 MaximumChunkZ = MAX_int32;
    int32 WorkerCount = 6;
    double TotalSeconds = 0.0;
    bool bCancelled = false;
};

namespace StandaloneWorldMesher
{
    using FClock = std::chrono::steady_clock;

    inline FIntVector CameraChunk(const FVector& PositionVoxels)
    {
        return FIntVector(
            FMath::FloorToInt(PositionVoxels.X / CHUNK_SIZE),
            FMath::FloorToInt(PositionVoxels.Y / CHUNK_SIZE),
            FMath::FloorToInt(PositionVoxels.Z / CHUNK_SIZE));
    }

    inline FStandaloneCpuClipmap Build(
        FStandaloneOwnerWorld& World, const FVector& CameraPositionVoxels, int32 WorkerCount = 6,
        const std::function<void(int32,FStandaloneCpuLevel&&)>& OnLevelReady = {},
        bool bRetainMeshData = true, std::atomic<bool>* Cancel = nullptr)
    {
        FStandaloneCpuClipmap Output;
        Output.WorkerCount = FMath::Clamp(WorkerCount,1,32);
        Output.CenterChunk = CameraChunk(CameraPositionVoxels);

        bool bHasStrate = false;
        int32 TopChunkZ = 0, BottomChunkZ = 0;
        if (World.Settings->bClampViewToStrate)
            bHasStrate = World.Manager->GetStrateChunkZBounds(
                Output.CenterChunk.Z,TopChunkZ,BottomChunkZ);
        VoxelClipmapDesiredTiles::ResolveVerticalBounds(
            Output.CenterChunk.Z,World.Settings->ViewDistanceUp,World.Settings->ViewDistanceDown,
            World.Settings->StrateViewMarginChunks,World.Settings->bClampViewToStrate,bHasStrate,
            TopChunkZ,BottomChunkZ,Output.MinimumChunkZ,Output.MaximumChunkZ);

        VoxelClipmapDesiredTiles::FParameters Parameters;
        Parameters.ClipRadius = World.ClipRadius;
        Parameters.MaxClipLevel = FMath::Clamp(World.MaxClipLevel,0,8);
        Parameters.RenderDistanceChunks = World.RenderDistanceChunks;
        TArray<FVoxelTileKey> AllTiles;
        VoxelClipmapDesiredTiles::Build(
            Output.CenterChunk,Output.MinimumChunkZ,Output.MaximumChunkZ,Parameters,AllTiles);
        std::array<std::vector<FVoxelTileKey>,9> TilesByLevel;
        for (const FVoxelTileKey& Tile : AllTiles)
            TilesByLevel[static_cast<size_t>(Tile.Level)].push_back(Tile);

        UVoxelMarchingCubesMesher::InitializeConsoleSwitches();
        const auto TotalStart = FClock::now();
        for (int32 Level = 0; Level <= Parameters.MaxClipLevel; ++Level)
        {
            if (Cancel && Cancel->load(std::memory_order_relaxed)) { Output.bCancelled = true; break; }
            const auto LevelStart = FClock::now();
            const std::vector<FVoxelTileKey>& Tiles = TilesByLevel[static_cast<size_t>(Level)];
            FStandaloneCpuLevel& LevelOutput = Output.Levels[static_cast<size_t>(Level)];
            LevelOutput.TileCount = Tiles.size();
            struct FTileResult { FVoxelMeshData Mesh; uint64 Samples = 0; };
            std::vector<FTileResult> Results(Tiles.size());
            std::atomic<size_t> Next{0};
            const int32 ThreadCount = FMath::Min<int32>(Output.WorkerCount,
                FMath::Max<int32>(1,static_cast<int32>(Tiles.size())));
            std::vector<std::thread> Threads;
            Threads.reserve(static_cast<size_t>(ThreadCount));
            for (int32 Worker = 0; Worker < ThreadCount; ++Worker)
            {
                Threads.emplace_back([&]()
                {
                    UVoxelMarchingCubesMesher Mesher;
                    Mesher.SetGenerator(World.Generator.get());
                    Mesher.bGenerateSkirts = World.bGenerateSkirts;
                    Mesher.SkirtCells = static_cast<float>(World.SkirtCells);
                    Mesher.LODOctaveDrop = World.LODOctaveDrop;
                    for (;;)
                    {
                        if (Cancel && Cancel->load(std::memory_order_relaxed)) break;
                        const size_t Index = Next.fetch_add(1,std::memory_order_relaxed);
                        if (Index >= Tiles.size()) break;
                        const FVoxelTileKey& Tile = Tiles[Index];
                        const int32 Extent = Tile.ExtentVoxels();
                        const int32 Cells = Level < World.FullResClipLevels
                            ? CHUNK_SIZE : FMath::Max(1,World.CoarseTileCells);
                        const int32 Step = FMath::Max(1,Extent / Cells);
                        int32 BandMin = MIN_int32, BandMax = MAX_int32;
                        if (World.StrateContentCutMinLevel < 9
                            && Level >= World.StrateContentCutMinLevel && bHasStrate)
                        {
                            BandMin = BottomChunkZ * CHUNK_SIZE;
                            BandMax = (TopChunkZ + 1) * CHUNK_SIZE;
                        }
                        int64 Samples = 0;
                        Results[Index].Mesh = Mesher.GenerateMesh(
                            Tile.OriginVoxels(),Step,Cells,nullptr,BandMin,BandMax,&Samples);
                        Results[Index].Samples = static_cast<uint64>(FMath::Max<int64>(0,Samples));
                    }
                });
            }
            for (std::thread& Thread : Threads) Thread.join();
            if (Cancel && Cancel->load(std::memory_order_relaxed)) { Output.bCancelled = true; break; }

            size_t VertexCount = 0, IndexCount = 0;
            for (const FTileResult& Result : Results)
            {
                if (!Result.Mesh.Triangles.IsEmpty()) ++LevelOutput.NonEmptyTiles;
                VertexCount += static_cast<size_t>(Result.Mesh.Vertices.Num());
                IndexCount += static_cast<size_t>(Result.Mesh.Triangles.Num());
                LevelOutput.DensitySamples += Result.Samples;
            }
            LevelOutput.Vertices.reserve(VertexCount);
            LevelOutput.Indices.reserve(IndexCount);
            for (FTileResult& Result : Results)
            {
                const uint32 BaseVertex = static_cast<uint32>(LevelOutput.Vertices.size());
                for (int32 I = 0; I < Result.Mesh.Vertices.Num(); ++I)
                {
                    const FVector& P = Result.Mesh.Vertices[I];
                    const FVector& N = Result.Mesh.Normals[I];
                    LevelOutput.Vertices.push_back({
                        {static_cast<float>(P.X*0.01),static_cast<float>(P.Y*0.01),static_cast<float>(P.Z*0.01)},
                        {static_cast<float>(N.X),static_cast<float>(N.Y),static_cast<float>(N.Z)}});
                }
                for (int32 Index : Result.Mesh.Triangles)
                    LevelOutput.Indices.push_back(BaseVertex + static_cast<uint32>(Index));
            }
            LevelOutput.Seconds = std::chrono::duration<double>(FClock::now()-LevelStart).count();
            LevelOutput.VertexCount = LevelOutput.Vertices.size();
            LevelOutput.IndexCount = LevelOutput.Indices.size();
            std::printf("clip level %d: %.3f s, %llu tiles (%llu nonempty), %llu vertices, %.2f M density samples\n",
                Level,LevelOutput.Seconds,
                static_cast<unsigned long long>(LevelOutput.TileCount),
                static_cast<unsigned long long>(LevelOutput.NonEmptyTiles),
                static_cast<unsigned long long>(LevelOutput.VertexCount),
                static_cast<double>(LevelOutput.DensitySamples)/1.0e6);
            std::fflush(stdout);
            if (OnLevelReady) OnLevelReady(Level,std::move(LevelOutput));
            if (!bRetainMeshData)
            {
                FStandaloneCpuLevel& Metadata = Output.Levels[static_cast<size_t>(Level)];
                Metadata.Vertices.clear();
                Metadata.Indices.clear();
                Metadata.Vertices.shrink_to_fit();
                Metadata.Indices.shrink_to_fit();
            }
        }
        Output.TotalSeconds = std::chrono::duration<double>(FClock::now()-TotalStart).count();
        std::printf("clipmap total: %.3f s on %d workers, %zu tiles\n",Output.TotalSeconds,
            Output.WorkerCount,static_cast<size_t>(AllTiles.Num()));
        return Output;
    }
}