# Detect coordinates within a shape

Theres 2 parts to my problem and they are related. I have a weird shape on my interface illustrated below, I am trying to randomly spawn MovieClips within its' boundaries but I am having some trouble finding a good way to do it.

**Question 1**: I can run an If condition to check with bitMapData.hitTest to see if the MovieClip has randomly spawn within this shape, if it doesn't simply retry with a new set of random coordinates. However, is there a better way? Like a way to only take into account coordinates within the shape? There will be plenty of MC spawned at one go so I am hoping to lessen the load, or at least find an efficient way to do this calculation.

**Question 2**: The MovieClips spawned within this shape will eventually have collision detection mechanics that will repel itself when interacted with. *Is there a way to contain them within this shape via some kind of boundary detection?*

If it was a square, we could easily have contained them with a quick check on all 4 edges, but not with this shape. Currently I am thinking of using bitMapData.hitTest again to detect for out-of-bounds after being repelled, but how do I know which Point() is the nearest 'edge' of this shape to return the MC to?

## Answers:

**For question 1**: I'm going to go on an assumption that you have some geometry data about the shape.

One method you can use to check if a point is within a shape is to take that point, then draw a line from that point to infinity (the edge of the screen) in one direction. Then count how many times that line intersects an edge of the shape. If it's odd, the point is within the shape (or on the edge) and if it's even, than that point is outside of the shape.

First link in google: https://www.geeksforgeeks.org/how-to-check-if-a-given-point-lies-inside-a-polygon/

Or can also try a more simple method (at the cost of doing more work): if the above shape is generated with all squares and rectangles and you know the point and size of all of those: can just do a check for the point vs all the squares and rectangles that make up the shape.

**For question 2**: As Organis mentioned, I'd go with a library like Box2D to do this. You'll most likely spend tons of time (that you may not want to) if you try to implement this alone.