调用静态函数是有点贵。您可以保存开销这样做：

Calling a static function is a bit expensive. You can save that overhead by doing this:

private var sqrtFunc = Math.sqrt;

private function dist(mmx:int, mmy:int, ox:int, oy:int):Number{
    return sqrtFunc((mmx-ox)*(mmx-ox)+(mmy-oy)*(mmy-oy));
}