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Physics2D.OverlapPoint mystery

Discussion in '2D' started by opeca, Apr 28, 2015.

  1. opeca

    opeca

    Joined:
    Sep 17, 2013
    Posts:
    19
    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:

    Code (CSharp):
    1. Vector3 wp = Camera.main.ScreenToWorldPoint(Input.mousePosition);
    2. var touchPos = new Vector2(wp.x, wp.y);
    3.          
    4. Collider2D hit = Physics2D.OverlapPoint(touchPos);
    5.  
    6. if (hit != null)
    7. {
    8.     ...
    9. }
    Thank you for your help!
     
    opeca, Apr 28, 2015
    #1

  2. MelvMay

    MelvMay

    Unity Technologies

    Joined:
    May 24, 2013
    Posts:
    11,544
    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.
     
    MelvMay, Apr 28, 2015
    #2
    Bunny83 likes this.

  3. opeca

    opeca

    Joined:
    Sep 17, 2013
    Posts:
    19
    Thank you for the explanation, I understand now, and the problem has fixed.
     
    opeca, Apr 28, 2015
    #3

  4. MelvMay

    MelvMay

    Unity Technologies

    Joined:
    May 24, 2013
    Posts:
    11,544
    You're most welcome, glad I could help.
     
    MelvMay, Apr 28, 2015
    #4

  5. skinner92

    skinner92

    Joined:
    Feb 23, 2014
    Posts:
    112
    Sorry for reviving such an old question, but I need to know what the line:

    Code (CSharp):
    1. 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?
     
    skinner92, Dec 18, 2015
    #5

  6. MelvMay

    MelvMay

    Unity Technologies

    Joined:
    May 24, 2013
    Posts:
    11,544
    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.
     
    MelvMay, Dec 18, 2015
    #6

  7. skinner92

    skinner92

    Joined:
    Feb 23, 2014
    Posts:
    112
    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:
    Code (CSharp):
    1. 1 << LayerMask.NameToLayer ("soldier")
    What can this mean?
     
    skinner92, Dec 18, 2015
    #7

  8. MelvMay

    MelvMay

    Unity Technologies

    Joined:
    May 24, 2013
    Posts:
    11,544
    If you click on the code you posted it takes you to the documentation. Here's the documentation for layers.
     
    MelvMay, Dec 19, 2015
    #8

  9. Kurius

    Kurius

    Joined:
    Sep 29, 2013
    Posts:
    412
    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
     
    Kurius, Dec 19, 2015
    #9