Can somebody please explain to me setMask?

[Kuromeku]

I don't understand at all? Is it bit-wise and shit, I'm not too keen on that. Same for setCategory, setCategoryBits and setMaskBits.

[rude]

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shape1:setCategory(1)
shape2:setCategory(2)

shape3:setMask(1) -- Does not collide with shape1
shape4:setMask(1, 2) -- Does not collide with shape1 nor shape2 (does collide with shape3)

[Kuromeku]

What is mask bits and category bits?

[u9_]

The box2d documentation will have a very good explanation of this (if i remember correctly), check it out

[Kuromeku]

It doesn't, that's why I'm asking here.

[surtic]

I think the explanation is that a category can be a number between 0 and 15 (i.e. 16 categories).
So when you want to specify a list of categories, you can either list them:

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shape:setCategory(1,3,10)

Or you can use a single number to represent this list. To do that, you calculate the sum of 2^category and use the result.
In this case: bits = 2^1+2^3+2^10 = 2+8+1024 = 1034. Then you use the "bits" function:

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shape:setCategoryBits(1034)

Why "bits"? Because when you look at 1034 as bits (in binary notation), you get 0000010000001010. You have '1' for the categories the shape belongs to, and '0' for the categories it doesn't belong to. And the same can be used for the mask (i.e. categories the shape can collide with).

So the short answer is, yes, it's bit-wise and shit...

[Kuromeku]

Hmm, I think I understand a bit better, thanks.

[athanazio]

rude,
I believe the comment you did

shape1:setCategory(1)
shape2:setCategory(2)

shape3:setMask(1) -- Does not collide with shape1
shape4:setMask(1, 2) -- Does not collide with shape1 nor shape2 (does collide with shape3)

is very clear and should go to the documentation !!

[rude]

... is very clear and should go to the documentation !!

Then please add it to the issue tracker, or I'll forget it! I'm not going to update the docs until the new documentation system [1] is in place (unless there are errors).

[1]: Yes, YET another one.