Detecting overlapping polygon2D colliders in Unity

Question

I'm trying to program an isometric building placement script. Each building has a PolygonCollider2D component on it with a trigger. When placing a new building, I'm trying to check if the PolygonCollider2D of the placed building overlaps with anything else (to check if placement is valid). My code is as follows:

Adjust the points of the new placed building collider based on the mouse position

Vector2[] points = polygonCollider2D.points;
points.SetValue(polygonCollider2D.points[0] + (Vector2)mousePosition, 0);
points.SetValue(polygonCollider2D.points[1] + (Vector2)mousePosition, 1);
points.SetValue(polygonCollider2D.points[2] + (Vector2)mousePosition, 2);
points.SetValue(polygonCollider2D.points[3] + (Vector2)mousePosition, 3);
polygonCollider2D.points = points;

Set up contact filter:

ContactFilter2D contactFilter2D = new ContactFilter2D();
contactFilter2D.useTriggers = true;
contactFilter2D.SetLayerMask(polygonCollider2D.gameObject.layer);

Check for collisions

List<Collider2D> list = new List<Collider2D>();
Debug.Log(polygonCollider2D.OverlapCollider(contactFilter2D, list));

However if there is already a building there, it still does not register an overlap. What am I missing / doing wrong ?

Thanks so much for the help!

Answer 1

Your code which sets the polygon collider points seems to be the issue here. If that code runs multiple times, it will repeatedly offset the collider further and further away from its original position. You probably don't want to be changing the actual collider; usually you should move object which has the collider. So you would replace those lines with something like this:

gameObject.transform.position = mousePosition;