噬血术：那一口红是从狼怪身上抽的

fx-drain

-- 贝塞尔: 怪 -> 拱顶 -> 掌心
local function DrainBezier(p, from, to)
    local cx, cy = (from.x + to.x) / 2, math.min(from.y, to.y) - 86
    local u = 1 - p
    return {
        x = u * u * from.x + 2 * u * p * cx + p * p * to.x,
        y = u * u * from.y + 2 * u * p * cy + p * p * to.y
    }
end

function lifeDrain:Update(dt)
    if self._left <= 0 then return end
    self._left = self._left - dt

    local tickDmg = 6 * dt
    self._target.hp = math.max(0, self._target.hp - tickDmg)
    self._caster.hp = math.min(self._caster.maxHp,
        self._caster.hp + tickDmg * self._rate * 2)      -- 数值一行

    if math.random() < dt * 26 then                      -- 生成血珠
        local from = { x = self._target:GetX() + (math.random() - 0.5) * 36,
                       y = self._target:GetY() - 46 - math.random() * 20 }
        SpawnDrop(from, self._caster:GetPalmPos(), 0.55 + math.random() * 0.4)
    end
end

function lifeDrain:DrawDrop(drop, dt)
    drop.p = drop.p + drop.spd * dt
    local pos = DrainBezier(math.min(1, drop.p), drop.from, drop.to)
    DrawGlowOrb(pos.x, pos.y, 4, COLOR_BLOOD)            -- 渐变红球
end