I have 2 objects, both have a Box collider 2D.

The first object is on the Level1 Sorting Layer and has a Tile script attached to it.

The second object is on the Level0 Sorting Layer and doesn't have any scripts.


The Tile script code is as follows:

void OnMouseDown()

Whenever I click the top tile, nothing prints in the console unless I click on the red area like I show in the image below (red area = [first box collider] minus [the two box colliders intersection area]).

enter image description here

Why this happens ? Why doesn't the OnMouseDown() function fire up simply when you click on its collider, since the top tile is on a higher sorting layer than the bottom tile. How does this work ? Doesn't sorting layer affect the 2D box collider ? (If I change the Z-axis of the top tile to -1, while keeping the bottom tile to 0, it works as expected.)


1 Answer 1


If you have stacked BoxCollider2Ds like that, Unity will only capture the mouse click on the topmost one.

You could:

  • Adjust the z-layer of your colliders (I think you do this by setting the renderer's "Order in Layer").

  • Enable/Disable your colliders in code based on which one is on top.

  • Do a RaycastAll, and process the click yourself.

  • \$\begingroup\$ what do you mean by "Unity will only capture the mouse click on the topmost one" ? how do you define the topmost ? this is what i am trying to achieve here. that's the point of the sorting layer ? at least i thought it was. apparently it is not. it seems like it only affects the drawing order. not the collider order as well. the order in layer is useless since the 2 objects are in the same sorting layer. so the only option is adjusting Z-layer, it is going to be hell when you have complex sorting layers and order in layers like in my game \$\endgroup\$
    – dimitris93
    Apr 12, 2015 at 14:42
  • \$\begingroup\$ @Shiro Order In Layer of your renderer will determine the layer of your collider. At least that is how I remember it working. Like I said, you could use RaycastAll, and simply check all the objects that are returned from that raycast, and action the one with the highest layer value. \$\endgroup\$
    – jgallant
    Apr 12, 2015 at 15:19
  • \$\begingroup\$ order in layer effects objects of the same layer. my objects are in different layers in the first place. I have already made this work by linecasting. i feel like this shouldn't be the way though. i liked your idea of enabling/disabling colliders in code. how efficient is that though ? I feel like unity might not be happy about changing it on runtime every 10 seconds. \$\endgroup\$
    – dimitris93
    Apr 12, 2015 at 15:27
  • \$\begingroup\$ I don't think disabling/enabling a collider is very demanding resource wise. You can always run some tests if it is a concern, but I would think it is fine. In fact, it may even speed things up considering that a bunch of your colliders wouldn't get updated. \$\endgroup\$
    – jgallant
    Apr 12, 2015 at 15:33
  • \$\begingroup\$ I guess it has to be better than having 5 times more colliders and them being always on. I ll try it out \$\endgroup\$
    – dimitris93
    Apr 12, 2015 at 15:34

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