BitMask

[adr]

Hey guys, me again for today. As I was reading the manual again… I notice bitmask doesn’t really cover how the bit mask looks like… so I was thinking maybe linking this example from chombee to show it off?

BitMask32 is a class for creating and combining binary bitmasks.

In [5]: BitMask32.allOff()
Out[5]: 0000 0000 0000 0000 0000 0000 0000 0000

In [6]: BitMask32.bit(1)
Out[6]: 0000 0000 0000 0000 0000 0000 0000 0010

In [7]: BitMask32.bit(0)
Out[7]: 0000 0000 0000 0000 0000 0000 0000 0001

In [8]: BitMask32.bit(2)
Out[8]: 0000 0000 0000 0000 0000 0000 0000 0100

It supports the operators &, <<, >>, ^ and |, which act like binary operators.

In [10]: BitMask32.bit(0) | BitMask32.bit(1) | BitMask32.bit(2)
Out[10]: 0000 0000 0000 0000 0000 0000 0000 0111

In [16]: BitMask32.bit(0) & BitMask32.bit(1) & BitMask32.bit(2)
Out[16]: 0000 0000 0000 0000 0000 0000 0000 0000

So if you want a NodePath to match a new bitmask, while still matching all the bitmaps it previously

matched, you can do:

np.setCollideMask(np.getCollideMask() | newBitMask)

The invertInPlace() methods inverts each bit:

In [47]: b = BitMask32.bit(0)

In [48]: b
Out[48]: 0000 0000 0000 0000 0000 0000 0000 0001

In [49]: b.invertInPlace()

In [50]: b
Out[50]: 1111 1111 1111 1111 1111 1111 1111 1110

You can use this if you want your NodePath to no longer match a particular bitmask, but to still match

all the other bitmasks it already matches.

In [51]: b = BitMask32.bit(0)

In [52]: c = BitMask32.bit(0) | BitMask32.bit(1) | BitMask32.bit(2)

In [53]: c
Out[53]: 0000 0000 0000 0000 0000 0000 0000 0111

In [54]: b.invertInPlace()

In [55]: b
Out[55]: 1111 1111 1111 1111 1111 1111 1111 1110

In [56]: c = c & b

In [57]: c
Out[57]: 0000 0000 0000 0000 0000 0000 0000 0110

An invert method would probably be more useful than invertInPlace. It has a lot of other methods too.

[rdb]

Hm, this is basic boolean mathematics, I’m not sure if we should cover it on the Panda manual at all. After all, the people who visit the Panda3D manual already know how to program.

[drwr]

After all, the people who visit the Panda3D manual already know how to program.

In theory, but often not in practice. I’m not opposed to laying some groundwork about basic programming concepts in the manual, when it’s not too distracting from the main point.

Similarly, I once believed that people wanting to use Panda already understood 3-D graphics in general, and so it wasn’t necessary to explain what a UV coordinate is. Until we got tons of people asking about this in the forums. Those questions went away when we added this information to the manual.

David

[tallmystcarpet]

Agreed with David, it was too tough for me to understand the bitmask section of the manual. I understood it with the zombie showcase.

[T_Rex]

I also agree with David. I’m clueless about bitmasks and how they work.

Yeah, I probably shouldn’t even be here, but I know I’m not the only noob to try using Panda.