磨刀石：三分切七分磨

 fx-whetstone

local Whetstone = {}
local KEY = { GAIN = 8 }

local sharp, slide = 0, nil
local dir = 1

function WS.Grind()
    if slide then return end
    dir = -dir
    slide = { t = 0, dir = dir }
    sharp = math.min(100, sharp + KEY.GAIN + math.random() * 4)
    SL:PlaySfx("grind_stone")
    SL:PlayBurst(SL:GetValue("bladeX") + 20,
                 SL:GetValue("stoneY") - 6, "spark", 4)
    SL:ShowSystemTips("锋利度 " .. math.floor(sharp) .. "%")
end

function WS.Tick(dt)
    if not slide then return end
    slide.t = slide.t + dt * 2.2
    -- 刀沿石面往复: 三角插值
    local k = slide.t
    local x = k < 0.5
        and (200 + 240 * k * 2)
        or (440 - 240 * (k - 0.5) * 2)
    SL:SetActorX("blade", x)
    SL:SetActorRotate("blade", -0.06)
    -- 火星碎屑: 推拉时偶尔溅出
    if math.random() < dt * 14 then
        SL:PlayBurst(x + 20, SL:GetValue("stoneY") - 4, "spark", 4)
    end
    if slide.t >= 1 then slide = nil end
end

function WS.TestCut()
    if sharp < 20 then
        SL:ShowSystemTips("还不够利 — 先磨")
        return
    end
    SL:PlayFxAt("cut_line", 160, 80, 0.6)
    if sharp >= 80 then
        SL:ShowSystemTips("一刀断纸! 锋利 " .. math.floor(sharp) .. "%")
        SL:PlaySfx("paper_cut")
    else
        SL:ShowSystemTips("纸没断透")
        SL:PlaySfx("whiff")
    end
end

return WS