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Fixed in 4.5.2
Box Collider 2D does not collide when its size is small (like 0.01)
Unity Version 4.5.0f6 (fd4616464986)
4.5 includes the latest Box2D which fixes a number of issues, one of which is correctly handling colliders (fixtures) that are too small. When Box2D encounters a collider that is too small it simply throws an assert. To counter this we perform the exact same checks that Box2D does including checking for vertex being too close, colinearity, and area being too small.
If any of these checks fail we simply don't create the Box2D collider. We don't push this as a warning to the console as this would cause a lot of spam to be generated. You will notice that the gizmo doesn't render in this case.
Upon further consideration, we feel that simply not rendering the gizmo isn't adequate so in Unity 4.5.1 (patch 2) we are adding a warning on the collider indicating that it couldn't complete the request to Box2D.
In all cases where you previously were using polygon/box to produce very thin colliders, it is highly recommended that you use the edge collider instead.
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Apr 06, 2018 05:14
To resolve this problem, just try to edit the collider of the Box Collider 3D that you append in an object.
Nov 25, 2015 03:55
Still not fixed?
Oct 01, 2015 10:48
Is this fixed yet ? 0.05 is still a lots for small particles which need colliders. To be honest its useful with 2d pixel graphics because 0.05 is 5 pixel if using 100 units representation with the physics engine. So basically it should support less than 0.05 otherwise i am stuck with graphics of 5x5 pixels.
Mar 29, 2015 14:41
I still have this issue with Unity 5.0 (Mac), box collider with a size of 0.24x0.05 will not collide depending on collision normal angle.
Aug 26, 2014 03:27
This problem is definitely not fixed.
Jul 24, 2014 11:36
Problem is NOT fixed. Unity 4.5.2
Jul 10, 2014 17:16
In unity3d 4.5.2 the problem remains.
Jul 05, 2014 15:07
This is quite unfortunate and unnecessary as <0.05m is not an unreasonable size for collisions. For those needing real-world physics but are working with small objects/characters (e.g. animals in a human world) one is left with few options but to work with arbitrary scales and conversions.
Jun 06, 2014 13:53
X or Y scale smaller or equal to 0.05 makes the collider gizmo disappear. With projects upgraded from older versions it can happen that collisions don't work.
Jun 01, 2014 22:13
polygon collider noticeably disappears from scene gradually when scaling object to smaller size