There is a simple way of handling collisions physics in Unity3D. All you need to be done before is to set correct values to object’s Layer field.
There is a feature called Layer Collision Mask in Unity3D. It works for both 2D and 3D modes. To access the collison mask go to Edit > Project Settings > Physics (or Edit > Project Settings > Physics2D for 2D mode). It will open the PhysicsManager setting in the Inspector tab:
Prevent collision between layers
Here you can see the layer collison mask with checkboxes. Each checkbox is responsible for detecting collisions between 2 game layers (first is vertical, second is horizontal). For example:
- The first checkbox in the top left is responsible for collisions between layers Default and Skills.
- The next one is responsible for collisions between Default and Background layers
- and so on…
So, to prevent collision between layers just disable a checkbox that represents this layers collision on the mask.