로블록스 유도 미사일 아키텍처: 비례 항법(PN) 유도 벡터, 3축 PID 조향 및 근접 신관 폭발

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

local MissileEngine = {}
MissileEngine.__index = MissileEngine

export type MissileConfig = {
    RootPart: BasePart,
    TargetPart: BasePart,
    ThrustForce: number,
    MotorBurnDuration: number,
    DragCoefficient: number,
    NavConstant: number,
    MaxTurnG: number,
    ProximityRadius: number,
}

export type MissileState = {
    Config: MissileConfig,
    ElapsedTime: number,
    PreviousDistance: number,
    IsDetonated: boolean,
    RayParams: RaycastParams,
}

local GRAVITY = Vector3.new(0, -Workspace.Gravity, 0)

function MissileEngine.New(missilePart: BasePart, target: BasePart): MissileState
    local rayParams = RaycastParams.new()
    rayParams.FilterType = RaycastFilterType.Exclude
    rayParams.FilterDescendantsInstances = { missilePart.Parent or missilePart }

    local state: MissileState = {
        Config = {
            RootPart = missilePart,
            TargetPart = target,
            ThrustForce = 350.0,
            MotorBurnDuration = 3.5,
            DragCoefficient = 0.002,
            NavConstant = 4.0,
            MaxTurnG = 25.0 * 32.2,
            ProximityRadius = 10.0,
        },
        ElapsedTime = 0,
        PreviousDistance = math.huge,
        IsDetonated = false,
        RayParams = rayParams,
    }
    return state
end

function MissileEngine.Step(state: MissileState, dt: number)
    if state.IsDetonated then return end

    local root = state.Config.RootPart
    local target = state.Config.TargetPart
    local cfg = state.Config

    state.ElapsedTime += dt
    local missilePos = root.Position
    local targetPos = target.Position
    local rangeVec = targetPos - missilePos
    local distance = rangeVec.Magnitude

    -- 근접 신관 감지: 최근접점(CPA) 통과 확인
    if distance < cfg.ProximityRadius or (state.PreviousDistance < cfg.ProximityRadius and distance > state.PreviousDistance) then
        state.IsDetonated = true
        root:Destroy()
        return
    end
    state.PreviousDistance = distance

    local missileVel = root.AssemblyLinearVelocity
    local targetVel = target.AssemblyLinearVelocity
    local relVel = targetVel - missileVel

    -- 시선(LOS) 회전 각속도 계산
    local losRate = rangeVec:Cross(relVel) / (distance * distance)
    local closingSpeed = -rangeVec:Dot(relVel) / distance

    -- 비례 항법(PN) 지령 횡가속도 계산
    local navAccel = Vector3.zero
    if closingSpeed > 0 and missileVel.Magnitude > 10 then
        local missileHeading = missileVel.Unit
        local rawAccel = losRate:Cross(missileHeading) * (cfg.NavConstant * closingSpeed)
        local clampedMagnitude = math.min(rawAccel.Magnitude, cfg.MaxTurnG)
        if rawAccel.Magnitude > 0.001 then
            navAccel = rawAccel.Unit * clampedMagnitude
        end
    end

    -- 로켓 추진력 및 공기역학 항력 연산
    local isBurning = state.ElapsedTime < cfg.MotorBurnDuration
    local forwardThrust = isBurning and (root.CFrame.LookVector * cfg.ThrustForce) or Vector3.zero
    local speed = missileVel.Magnitude
    local dragForce = -missileVel * (speed * cfg.DragCoefficient)

    local totalAccel = forwardThrust + navAccel + dragForce + GRAVITY
    root.AssemblyLinearVelocity = missileVel + (totalAccel * dt)

    -- 미사일 헤딩 노즈를 속도 벡터 방향으로 정렬
    if speed > 5 then
        root.CFrame = CFrame.lookAt(missilePos, missilePos + root.AssemblyLinearVelocity)
    end
end

return MissileEngine