背刺：绕到它身后，刀刀双倍

 fx-backstab

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-- @file        BackStab.lua
-- @brief       背刺 —— 绕到它身后，刀刀双倍
--              客户端表现模块：配置表 / 朝向判定构件 / 绕后步状态机 / 定时器
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local BackStab = {}

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-- 配置与常量
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local CONST = {
    BEHIND_BAND   = 70,         -- 背后判定带七十步
    CRIT_AMP      = 2.0,        -- 背后双倍
    BASE_DMG      = 12,         -- 正面十二
    STEP_LIFE     = 0.3,        -- 绕后步零点三秒
    STEP_CD       = 5.0,        -- 绕后冷却五秒
    STEP_OFFSET   = 54,         -- 落在它身后五十四步

    -- 颜色
    COLOR_STAB    = "#a89ae0",  -- 背刺青
    COLOR_DEEP    = "#3a2a6e",  -- 深紫
    COLOR_GHOST   = "#ece4ff",  -- 刃白

    ZORDER_GROUND = 118,
    ZORDER_STEP   = 133,
    ZORDER_EFFECT = 135,

    AUTOINC_BASE  = 958000,
}

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-- 模块内部状态
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local _stepT      = 0              -- 绕后步余时
local _stepFrom   = 0
local _stepTo     = 0
local _cdLeft     = 0
local _scheduler  = nil
local _autoInc    = 0

local m_cos = math.cos
local m_sin = math.sin

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-- 辅助函数
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local function GenID(prefix)
    _autoInc = _autoInc + 1
    return string.format("%s_%d", prefix or "BST", CONST.AUTOINC_BASE + _autoInc)
end

local function GetActorPos(actorID)
    if not actorID then return nil end
    local x = SL:GetValue("ACTOR_POSITION_X", actorID)
    local y = SL:GetValue("ACTOR_POSITION_Y", actorID)
    if not x or not y then return nil end
    return { x = x, y = y }
end

local function SafeRemove(node)
    if node and not GUI:Widget_IsNull(node) then
        GUI:removeFromParent(node)
    end
end

local function ShowTip(msg)
    if msg and msg ~= "" then SL:ShowSystemTips(msg) end
end

---背后判定圈构件：怪脚下的一圈亮环
local function CreateBehindRing(x)
    local node = GUI:Layout_Create(GUI:Attach_SceneF(), GenID("Ring"), x, 6, 0, 0, false)
    GUI:setLocalZOrder(node, CONST.ZORDER_STEP)
    for i = 1, 22 do
        local a1 = (i - 1) / 22 * 6.28
        local a2 = i / 22 * 6.28
        GUI:DrawLine_Create(node, string.format("r_%d", i), 0, 0, 2.5,
            m_cos(a1) * 34, m_sin(a1) * 12, m_cos(a2) * 34, m_sin(a2) * 12,
            CONST.COLOR_STAB, 210)
    end
    return node
end

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-- 朝向判定：怪面朝右玩家在左即背后
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local function IsBehind(myX, foeX, foeDir)
    if foeDir == 2 and myX < foeX - 10 then return true end
    if foeDir == 6 and myX > foeX + 10 then return true end
    return false
end

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-- 绕后步
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function BackStab.Step()
    if _cdLeft > 0 or _stepT > 0 then return end
    local tp = GetActorPos(SL:GetValue("MARK_TARGET_ID"))
    local mp = GetActorPos(SL:GetValue("USER_ID"))
    if not tp or not mp then return end
    _cdLeft = CONST.STEP_CD
    _stepT = CONST.STEP_LIFE
    _stepFrom = mp.x
    _stepTo = tp.x + (mp.x > tp.x and CONST.STEP_OFFSET or -CONST.STEP_OFFSET)
    ShowTip("绕后——抢它转身的半拍")
end

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-- 定时器：绕后步推进与背刺结算
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if not _scheduler then
    _scheduler = SL:Schedule(function(dt)
        _cdLeft = math.max(0, _cdLeft - dt)
        if _stepT > 0 then
            _stepT = _stepT - dt
            local k = 1 - math.max(0, _stepT) / CONST.STEP_LIFE
            local mp = GetActorPos(SL:GetValue("USER_ID"))
            if mp then
                SL:FlyActorTo(_stepFrom + (_stepTo - _stepFrom) * k)
                SL:DropGhost()
            end
            if _stepT <= 0 then
                _stepT = 0
            end
            return
        end
        _atkT = (_atkT or 1.2) - dt
        if _atkT <= 0 then
            _atkT = 1.2
            local myID = SL:GetValue("USER_ID")
            local mp = GetActorPos(myID)
            local tid = SL:GetValue("MARK_TARGET_ID")
            local tp = tid and GetActorPos(tid)
            if mp and tp and IsBehind(mp.x, tp.x, SL:GetValue("ACTOR_DIR", tid)) then
                local vd = CONST.BASE_DMG * CONST.CRIT_AMP
                SL:ActorHurt(tid, vd)
                SL:TipAbove(tid, "-" .. vd)
                SL:ScreenShake(3, 0.16)
            else
                SL:ActorHurt(tid, CONST.BASE_DMG)
            end
        end
    end, 0.02)
end

SL:ScheduleOnce(function()
    ShowTip("技能已加载: 背刺 (调试按钮触发)")
end, 1.0)

return BackStab