절차적 3D 복셀 시스템: 밀도 필드, 마칭 큐브 등가면 생성 및 청크 스트리밍

--!strict
local Workspace = game:GetService("Workspace")
local AssetService = game:GetService("AssetService")

local TRIANGULATION_TABLE = require(script.MarchingCubesTables).Triangles
local EDGE_TABLE = require(script.MarchingCubesTables).Edges

local VoxelChunk = {}
VoxelChunk.__index = VoxelChunk

export type ChunkData = {
    ChunkCoord: Vector3,
    Size: number,
    Resolution: number,
    DensityField: {number},
    MeshPart: MeshPart?,
    EditableMesh: any?,
}

function VoxelChunk.new(coord: Vector3, size: number, resolution: number): ChunkData
    local self = setmetatable({}, VoxelChunk)
    self.ChunkCoord = coord
    self.Size = size
    self.Resolution = resolution
    self.DensityField = table.create((resolution + 1) ^ 3, 0)
    return self
end

function VoxelChunk:GetIndex(x: number, y: number, z: number): number
    local res = self.Resolution + 1
    return x + y * res + z * res * res + 1
end

function VoxelChunk:EvaluateDensity(worldX: number, worldY: number, worldZ: number): number
    -- 3D 밀도 함수: 양수 = 암석, 음수 = 공기
    local baseHeight = 50 - worldY
    local noise3D = math.noise(worldX * 0.02, worldY * 0.02, worldZ * 0.02) * 25
    local caveNoise = math.abs(math.noise(worldX * 0.04, worldY * 0.04, worldZ * 0.04)) * 30
    return baseHeight + noise3D - caveNoise
end

function VoxelChunk:PopulateDensity()
    local res = self.Resolution
    local step = self.Size / res
    local origin = self.ChunkCoord * self.Size

    for z = 0, res do
        for y = 0, res do
            for x = 0, res do
                local worldPos = origin + Vector3.new(x * step, y * step, z * step)
                local idx = self:GetIndex(x, y, z)
                self.DensityField[idx] = self:EvaluateDensity(worldPos.X, worldPos.Y, worldPos.Z)
            end
        end
    end
end

function VoxelChunk:BuildMesh(parent: Instance)
    local editableMesh = AssetService:CreateEditableMesh()
    local res = self.Resolution
    local step = self.Size / res
    local isoLevel = 0.0

    -- 큐브 모서리 상대 오프셋
    local cornerOffsets = {
        Vector3.new(0, 0, 0), Vector3.new(step, 0, 0), Vector3.new(step, step, 0), Vector3.new(0, step, 0),
        Vector3.new(0, 0, step), Vector3.new(step, 0, step), Vector3.new(step, step, step), Vector3.new(0, step, step)
    }

    for z = 0, res - 1 do
        for y = 0, res - 1 do
            for x = 0, res - 1 do
                local cubeIndex = 0
                local cornerDensities = {}
                local cornerPositions = {}

                for i = 1, 8 do
                    local offset = cornerOffsets[i]
                    local gx = x + math.round(offset.X / step)
                    local gy = y + math.round(offset.Y / step)
                    local gz = z + math.round(offset.Z / step)
                    local d = self.DensityField[self:GetIndex(gx, gy, gz)]
                    cornerDensities[i] = d
                    cornerPositions[i] = Vector3.new(x * step, y * step, z * step) + offset

                    if d > isoLevel then
                        cubeIndex = bit32.bor(cubeIndex, bit32.lshift(1, i - 1))
                    end
                end

                if cubeIndex > 0 and cubeIndex < 255 then
                    local triList = TRIANGULATION_TABLE[cubeIndex + 1]
                    for t = 1, #triList, 3 do
                        local e1, e2, e3 = triList[t], triList[t + 1], triList[t + 2]
                        -- 모서리 보간 및 정점 생성
                        local v1 = self:InterpolateEdge(e1, cornerPositions, cornerDensities, isoLevel)
                        local v2 = self:InterpolateEdge(e2, cornerPositions, cornerDensities, isoLevel)
                        local v3 = self:InterpolateEdge(e3, cornerPositions, cornerDensities, isoLevel)

                        local id1 = editableMesh:AddVertex(v1)
                        local id2 = editableMesh:AddVertex(v2)
                        local id3 = editableMesh:AddVertex(v3)
                        editableMesh:AddTriangle(id1, id2, id3)
                    end
                end
            end
        end
    end

    local meshPart = AssetService:CreateMeshPartAsync(Content.fromObject(editableMesh))
    meshPart.Position = self.ChunkCoord * self.Size
    meshPart.Anchored = true
    meshPart.Parent = parent
    self.MeshPart = meshPart
end

return VoxelChunk