VoxelForge/Source/VoxelForge/Private/VoxelClipmapDesiredTiles.h

#pragma once

#include "VoxelTypes.h"

namespace VoxelClipmapDesiredTiles
{
    FORCEINLINE int64 FloorDivWide(int64 Value, int64 Divisor)
    {
        if (Divisor <= 0) { return 0; }
        const int64 Quotient = Value / Divisor;
        const int64 Remainder = Value % Divisor;
        return Remainder < 0 ? Quotient - 1 : Quotient;
    }

    FORCEINLINE int64 CeilDivWide(int64 Value, int64 Divisor)
    {
        if (Divisor <= 0) { return 0; }
        const int64 Quotient = Value / Divisor;
        const int64 Remainder = Value % Divisor;
        return Remainder > 0 ? Quotient + 1 : Quotient;
    }

    FORCEINLINE int32 ClampInt32(int64 Value)
    {
        return static_cast<int32>(FMath::Clamp<int64>(Value, MIN_int32, MAX_int32));
    }

    struct FParameters
    {
        int32 ClipRadius = 3;
        int32 MaxClipLevel = 4;
        int32 RenderDistanceChunks = 0;
    };

    FORCEINLINE int32 FloorDiv(int32 Value, int32 Divisor)
    {
        if (Divisor <= 0) { return 0; }
        const int32 Quotient = Value / Divisor;
        const int32 Remainder = Value % Divisor;
        return Remainder < 0 ? Quotient - 1 : Quotient;
    }

    FORCEINLINE FIntVector FloorDiv(const FIntVector& Value, int32 Divisor)
    {
        return FIntVector(FloorDiv(Value.X, Divisor), FloorDiv(Value.Y, Divisor),
                          FloorDiv(Value.Z, Divisor));
    }

    FORCEINLINE int32 CeilDiv(int32 Value, int32 Divisor)
    {
        if (Divisor <= 0) { return 0; }
        const int32 Quotient = Value / Divisor;
        const int32 Remainder = Value % Divisor;
        return Remainder > 0 ? Quotient + 1 : Quotient;
    }

    FORCEINLINE void AlignedRingBounds(const FIntVector& Center, int32 Radius, int32 Alignment,
                                       FIntVector& OutMin, FIntVector& OutMax)
    {
        const auto AlignAxis = [Radius, Alignment](int32 CenterAxis,
                                                  int32& OutAxisMin, int32& OutAxisMax)
        {
            const int64 SafeRadius = FMath::Max<int64>(0, Radius);
            const int64 SafeAlignment = FMath::Max<int64>(1, Alignment);
            const int64 BaseMin = static_cast<int64>(CenterAxis) - SafeRadius;
            const int64 BaseEnd = static_cast<int64>(CenterAxis) + SafeRadius + 1;
            OutAxisMin = ClampInt32(FloorDivWide(BaseMin, SafeAlignment) * SafeAlignment);
            OutAxisMax = ClampInt32(CeilDivWide(BaseEnd, SafeAlignment) * SafeAlignment - 1);
        };
        AlignAxis(Center.X, OutMin.X, OutMax.X);
        AlignAxis(Center.Y, OutMin.Y, OutMax.Y);
        AlignAxis(Center.Z, OutMin.Z, OutMax.Z);
    }

    FORCEINLINE int32 OuterShellRadius(const FParameters& Parameters, int32 Radius, int32 MaxLevel)
    {
        if (Parameters.RenderDistanceChunks <= 0)
        {
            return Radius;
        }
        const int32 SafeLevel = FMath::Clamp(MaxLevel, 0, 8);
        const int64 Scale = int64{1} << static_cast<uint32>(SafeLevel);
        const int64 Numerator = static_cast<int64>(Parameters.RenderDistanceChunks)
            + Scale - 1;
        const int64 DesiredRadius = Numerator / Scale;
        return static_cast<int32>(FMath::Clamp<int64>(
            FMath::Max<int64>(Radius, DesiredRadius), 0, MAX_int32));
    }

    FORCEINLINE void OuterShell(const FParameters& Parameters, int32 Radius, int32 MaxLevel,
                                int32& OutLevel, int32& OutRadius)
    {
        OutLevel = MaxLevel;
        OutRadius = OuterShellRadius(Parameters, Radius, MaxLevel);
    }

    FORCEINLINE void ResolveVerticalBounds(
        int32 CenterChunkZ, int32 ViewDistanceUp, int32 ViewDistanceDown,
        int32 StrateViewMarginChunks, bool bClampToStrate, bool bHasStrate,
        int32 StrateTopChunkZ, int32 StrateBottomChunkZ,
        int32& OutMinChunkZ, int32& OutMaxChunkZ)
    {
        OutMinChunkZ = MIN_int32;
        OutMaxChunkZ = MAX_int32;
        if (!bClampToStrate)
        {
            return;
        }

        OutMinChunkZ = ClampInt32(static_cast<int64>(CenterChunkZ) - ViewDistanceDown);
        OutMaxChunkZ = ClampInt32(static_cast<int64>(CenterChunkZ) + ViewDistanceUp);
        if (bHasStrate)
        {
            OutMinChunkZ = ClampInt32(static_cast<int64>(StrateBottomChunkZ) - StrateViewMarginChunks);
            OutMaxChunkZ = ClampInt32(static_cast<int64>(StrateTopChunkZ) + StrateViewMarginChunks);
        }
    }

    FORCEINLINE void Build(const FIntVector& Center, int32 MinChunkZ, int32 MaxChunkZ,
                           const FParameters& Parameters, TArray<FVoxelTileKey>& OutTiles)
    {
        OutTiles.Reset();
        const int32 Radius = FMath::Max(1, Parameters.ClipRadius);
        const int32 MaxLevel = FMath::Clamp(Parameters.MaxClipLevel, 0, 8);
        const int32 OuterRadius = OuterShellRadius(Parameters, Radius, MaxLevel);
        FIntVector PreviousRingMin = FIntVector::ZeroValue;
        FIntVector PreviousRingMax = FIntVector::ZeroValue;

        for (int32 Level = 0; Level <= MaxLevel; ++Level)
        {
            const int32 Pow = static_cast<int32>(uint32{1} << static_cast<uint32>(Level));
            const FIntVector CenterLevel = FloorDiv(Center, Pow);
            const int32 LevelRadius = (Level == MaxLevel) ? OuterRadius : Radius;

            // Every finer shell must end on a complete child-pair boundary so a coarser tile is
            // either wholly inside it or wholly outside it. The outermost ring has no coarser
            // neighbour and needs no alignment.
            const int32 RingAlignment = Level < MaxLevel ? 2 : 1;
            FIntVector RingMin, RingMax;
            AlignedRingBounds(CenterLevel, LevelRadius, RingAlignment, RingMin, RingMax);

            int64 TileMinZ = RingMin.Z;
            int64 TileMaxZ = RingMax.Z;
            if (LevelRadius > Radius && MinChunkZ != MIN_int32)
            {
                TileMinZ = FMath::Max<int64>(TileMinZ, FloorDiv(MinChunkZ, Pow));
                TileMaxZ = FMath::Min<int64>(TileMaxZ, FloorDiv(MaxChunkZ, Pow));
            }

            for (int64 Z = TileMinZ; Z <= TileMaxZ; ++Z)
            for (int64 Y = RingMin.Y; Y <= RingMax.Y; ++Y)
            for (int64 X = RingMin.X; X <= RingMax.X; ++X)
            {
                const FIntVector Tile(static_cast<int32>(X), static_cast<int32>(Y),
                                      static_cast<int32>(Z));
                const int64 TileBottomChunkZ = static_cast<int64>(Tile.Z) * Pow;
                const int64 TileTopChunkZ = (static_cast<int64>(Tile.Z) + 1) * Pow - 1;
                if (TileTopChunkZ < MinChunkZ || TileBottomChunkZ > MaxChunkZ)
                {
                    continue;
                }

                if (Level > 0)
                {
                    const bool bCovered =
                        (2 * static_cast<int64>(Tile.X) >= PreviousRingMin.X)
                        && (2 * static_cast<int64>(Tile.X) + 1 <= PreviousRingMax.X)
                        && (2 * static_cast<int64>(Tile.Y) >= PreviousRingMin.Y)
                        && (2 * static_cast<int64>(Tile.Y) + 1 <= PreviousRingMax.Y)
                        && (2 * static_cast<int64>(Tile.Z) >= PreviousRingMin.Z)
                        && (2 * static_cast<int64>(Tile.Z) + 1 <= PreviousRingMax.Z);
                    if (bCovered)
                    {
                        continue;
                    }
                }

                OutTiles.Emplace(Tile, Level);
            }

            PreviousRingMin = RingMin;
            PreviousRingMax = RingMax;
        }
    }
}