Lua贝塞尔曲线：控制点的平滑轨迹

local function lerp(a, b, t)
    return a + (b - a) * t          -- 直线插值，轨迹生硬
end

local function bezier(p0, p1, p2, t)
    local u = 1 - t
    return u * u * p0 + 2 * u * t * p1 + t * t * p2
end
local function trail(t)
    local x = bezier(0, 50, 100, t)
    local y = bezier(0, 80, 0, t)
    sendmsg(actor, 1, "轨迹(" ..
        math.floor(x) .. "," .. math.floor(y) .. ")")
end
trail(0.5)                          -- 中点恰在 (50,40)