Blend Node Mask Parameter

[michael]

Since I keep forgetting how to do this....

Blend nodes have a weird parameter on them called Mask - it lets you specify what combination of Tx Ty Tz Rx Ry Rz Sx Ry Rz to take from each input.

this is called a "Bit Mask"

and here is how to figure then out:

with a default blend object in your scene (blend1) and something wired into it...anything, a null

open a python shell and type:

>>> bmask = (then click on the Mask 1 parameter of blend1 and drag it here)

you should have this: 

>>> bmask = hou.parm('/obj/blend1')

hit enter

now type

>>> bmask.eval()

hit enter

>>> 511

what the hell?

here's how to decrypt this number

if you turn OFF all the TRS of blend1/Mask1

and type the above again you'l get:

>>> 0

turn ON TX

>>> 1

turn OFF TX and turn ON TY

>>> 2

turn OFF TY and turn ON TZ

>>> 4

and so on....each one is double the one before.

so how did we get 511?

we ADD each one to get a total > 1 (tx) + 2 (ty) + 4 (tz) + 8 (rx) + 16 (ry) + 32 (rz) + 64 (sx) + 128 (sy) + 256 (sz) = 511

so to manipulate this parameter with HOM we can set this parameter to the TOTAL that we want.

if we want TX RY and SZ we'd use: ( 1 + 16 + 256 = 273 )

bmask.set(273)

[f1480187]

If you convert the nine boxes into binary sequence, it will be more intuitive:

Binary    Decimal      Axes
SSSRRRTTT
zyxzyxzyx
000000000       0      None
000000001       1        Tx
000000010       2        Ty
000000100       4        Tz
000001000       8        Rx
000010000      16        Ry
000100000      32        Rz
001000000      64        Sx
010000000     128        Sy
100000000     256        Sz
111111111     511       All
100010001     273    TxRySz
000010111      23  TxTyTzRy

Note the reversed order Houdini uses internally (Sz Sy Sx Rz Ry Rx Tz Ty Tx) for the mask. By using bitwise OR operator, you build up axes you need:

# Using decimal numbers.
bmask.set(273)
bmask.set(1 | 16 | 256)

# Using binary numbers.
bmask.set(0b100010001)
bmask.set(0b000000001 | 0b000010000 | 0b100000000)

# Using named constants.
TX = 0b000000001
RY = 0b000010000
SZ = 0b100000000
bmask.set(TX | RY | SZ)

The last one is how it's usually being used. It's human-readable in code. You may also make use of AND and other bitwise operators:

NO_SCALE = 0b000111111
bmask.set(bmask.eval() & NO_SCALE)

 

Edited November 9, 2016 by f1480187

[michael]

thanks for this addition...

but I have to say that binary is not what most people want to see