efficent select points on large points cloud

Hello alls,

I'm trying to select some points inside a fast points cloud around the mouse and want to select them while moving the mouse. I saw the code samples for points selection and i made what i want and, for small points cloud, it works well.

I'm doing that with mousemove event, but every time mousemove is called i need to check if every point inside the points cloud is inside my area and for millions of points it take a while and meantime the interface is freezed and not work as intended. I've also tried to use FindClosestVertex, but, again, with 4 milions points it take about 1.5 seconds.

Is there any efficent way to do this?