咬住不放的追踪弹

fx-homing

function homingMissile:Update(dt)
    local tx = self._target:GetX() - self._x
    local ty = (self._target:GetY() - 30) - self._y
    local want = math.atan2(ty, tx)                    -- 目标方向
    local cur  = math.atan2(self._vy, self._vx)        -- 当前朝向

    local diff = want - cur
    while diff >  math.pi do diff = diff - 2 * math.pi end
    while diff < -math.pi do diff = diff + 2 * math.pi end

    local maxTurn = self._turnRate * dt                -- 转向力钳制
    diff = math.max(-maxTurn, math.min(maxTurn, diff))
    local na = cur + diff

    self._vx = math.cos(na) * self._speed
    self._vy = math.sin(na) * self._speed
    self._x = self._x + self._vx * dt
    self._y = self._y + self._vy * dt

    local dist = math.sqrt(tx * tx + ty * ty)
    if dist <= self._speed * dt + 26 then              -- 步长跨越命中
        self:Explode()
        return false
    end
    return true
end