Check out example codes for "collision layer an collision mask godot". It will help you in understanding the concepts better.
Code Example 1
Collision mask bit is for choosing what layer should be collided. Let's assume we set collision layer and mask layer as below. Player node : collision layer is on 1st bit / mask layer is on 2nd,3rd bit Enemy node : collision layer is on 2nd bit / mask layer is on 1st bit Object node : collision layer is on 3rd bit / mask layer is on 1st bit then, Player mask(2) == Enemy layer(2) Player mask(3) == Object layer(3) so, Player can be collided with Enemy and Object. but Enemy nodes are not collided each other or Object nodes. Because Enemy mask(1) != Enemy layer(2) / Enemy mask(1) != Object layer(3)
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