Collision filter mask works ugly

[Chaz]

Hello. I guess I don't understand how to work with collision filtering.
For example, I have object with filter group = 10 and filter mask = 1, and then I cast a ray with filter group = 20, and it works good - ray ignores object.
But if I change filter mask of the object, for example, filter mask = 25 then it gives collision between ray and object.
Why it so? I just want to make collision only between objects with filter group 10 and 20, not between 10 and 25.

[Erwin Coumans]

Collision masks and filters work bit-wise.

Good luck!

[Chaz]

Collision masks and filters work bit-wise.

Good luck!

Do you mean that object with collision flag 10 and mask 25 will be collide with all objects which has collision flag less than 25 ?

[drleviathan]

He means that if you write 10 in 16-bit binary you get: 0000 0000 0000 1010. What matters is that two bits are set: the second bit from right, which represents the value 2, and the fourth bit from right, which represents the value 8 -- add them together and you get 10. Similarly 25 would look like: 0000 0000 0001 1001 = 1 + 8 + 16. Each bit of the collision filter represents a collision group that can be enabled or disabled -- you only have 16 of them because they are stored in a 16-bit value.

Collision filter 10 is in two groups (2 + 8) and collides with something with collision filter 25 (1 + 8 + 16) because they are both in group 8. Meanwhile collision filter 20 (4 + 16) shares no groups with 10.

[Chaz]

He means that if you write 10 in 16-bit binary you get: 0000 0000 0000 1010. What matters is that two bits are set: the second bit from right, which represents the value 2, and the fourth bit from right, which represents the value 8 -- add them together and you get 10. Similarly 25 would look like: 0000 0000 0001 1001 = 1 + 8 + 16. Each bit of the collision filter represents a collision group that can be enabled or disabled -- you only have 16 of them because they are stored in a 16-bit value.

Collision filter 10 is in two groups (2 + and collides with something with collision filter 25 (1 + 8 + 16) because they are both in group 8. Meanwhile collision filter 20 (4 + 16) shares no groups with 10.

I guess I got it. That's why in manual is written "This means you can have up to 15 different groups, and 15 different masks."
So I just have to assign to each object collision filter which is power of 2.
Thanks!
p.s. sry for my bad English