Create a collider for area created by mouse

Unity Answers addresses questions with a single specific issue. Unity Forums is a better fit for high-level design questions like yours.

You have a number of individual technical problems:

• How to draw a line

• How to save a path

• How to detect when a path is closed

• How to detect what balls are inside the path

In turn each one of the above has a number of technical issues/decisions. Addressing the specific question of building a collider, you can build a mesh using an arbitrary path using this script from the Unity Wiki.

http://wiki.unity3d.com/index.php/Triangulator

A better solution to run through the line segments comparing all balls to each segment. For a ball to be inside the path, the ball must be on the same side of all line segments.

Thanks for your comment, but now I've drawn path, auto close the path if it not closed. My problem now is detect how many balls inside and I think I can check by the collision. However, I dont know how to do that. How to create the collision for the area that created by the closed path. That is my question. Thanks for your consideration.

Are you using a line renderer? If so while adding points to the line rendered you need to add them in the edge collider too. I can show you a similar script to mine.