Physics2D.OverlapPoint mystery

Unity Engine
1

Hello All,

Of course, may not a mystery - and experienced persons may can help to me - but a strange issue has just appeared while I trying 2D features.

I’ have two different sprites, background and a Wall.
Background sprite renderer has -1 as order in layer, Wall has 0.

I would like to detect Wall with mouse press, and sometimes it’s okay, but sometimes Physics2D.OverlapPoint detect Background sprite first, but fo course it looks behind the Wall in the scene.

I tried to find out, what’s happening with Physics2D.OverlapPointAll, and seems, in some cases order of detection has changed, like:

  1. Background
  2. Wall

Does anybody experienced similar issue, or what I’m doing wrong?

The code for detect the overlapping is:

Vector3 wp = Camera.main.ScreenToWorldPoint(Input.mousePosition);
var touchPos = new Vector2(wp.x, wp.y);
          
Collider2D hit = Physics2D.OverlapPoint(touchPos);

if (hit != null)
{
    ...
}

Thank you for your help!

2

Physics is completely decoupled from sprites, it knows nothing about rendering thus it’s not related to rendering orders etc.

The ray/line/shape casts are order by distance and the overlap checks are ordered by Z order of the transform. The only reason the Z order of the transform is used is that the overlap checks allow you to select a Z range for the query. If the Z is the same then the order is undefined.

When you use the overlap calls that only return a single collider then you’ll only get the first one in the list using the sorting rules above i.e. the lowest Z or undefined.

1 Like
3

Thank you for the explanation, I understand now, and the problem has fixed.

4

You’re most welcome, glad I could help.

5

Sorry for reviving such an old question, but I need to know what the line:

Collider2D hit = Physics2D.OverlapPoint (v2TouchedPos)

actually does. I mean, “hit” can never be null in a real game, right? You are always going to click/touch into something that does exist.

I’m asking this because in a “shooting” method that I’ve come across, I’ve seen a line that says “if (hit != null) …”. It’s never going to be null, right?

6

If you read the documentation, it tells you that it returns NULL if no collider was found. The return type is Collider2D which is a reference type which can be NULL.

7

My fault, I thought that method would detect whatever gameObject.

One more related question MelvMay: using the Physics2D.Raycast method, I’ve come across with an argument that says:

1 << LayerMask.NameToLayer ("soldier")

What can this mean?

8

If you click on the code you posted it takes you to the documentation. Here’s the documentation for layers.

9

It means the Raycast will only consider Colliders belonging to a Layer called “soldier”. It will ignore all other Colliders in its path.
http://docs.unity3d.com/ScriptReference/Physics2D.Raycast.html