prim expression for source volume activation

[tagosaku]

Hi, I am looking for expression to automatically activate source volume node in DOP by input object(VDB, houdiniSDF). This is because sim is broken, if the sourceVolume set to collision but there is no SDF primitive.

 

my idea is that the inside of the node, sourcevolume > SOP solver(source_density)>objectMerge(fetch_density). After this node, I add primitiveWrangle:

if(@name == "density" || @name == "surface")
f@activeSwitch =1;
 

then I made float parameter(activation), and paste expression.

prim(".", "activeSwitch", 0)
 

After that, I plan to paste the parameter value to sourcevolume>activation. Then it should automatically set activation ON/OFF.

The wrangleVEX is working but prim's expression is not working. How can I fix it??

[f1480187]

You didn't specify primitive number argument. VEX and HScript Expressions syntax are different.

Another options:

1. Use this expression in-place with dot replaced by the path to the Wrangle, without creating an extra-parameter on the Wrangle.

2. Don't create Wrangle. Check for the string "name" attribute in-place using prims() function.

You can't use "foo" == "foo", it only works for numbers in HScript Expressions. You need to use strcmp(). It returns zero if strings are equal and non-zero if not:

(strcmp(prims("/path/to/operator", 0, "name"), "density") == 0)  ||  (strcmp(prims("/path/to/operator", 0, "name"), "surface") == 0)

Sometimes, you can encounter an elegant uses:

• "!strcmp(x, y)" instead of "strcmp(x, y) == 0" for true check;
• "!!strcmp(x, y)" instead of "strcmp(x, y) != 0" for false check.

prims_and_strcmp.hipnc

Edited June 24, 2017 by f1480187
correct prims syntax

[tagosaku]

actually code should be :

(strcmp(prim("/path/to/operator", 0, "name", 0), "density") == 0)  ||  (strcmp(prim("/path/to/operator", 0, "name", 0), "surface") == 0)

However, this method won't work because prim does not return density name but will return actual density value. I need to figure out different way.

Edited June 24, 2017 by tagosaku

[f1480187]

My mistake, prims usage syntax should be prims(somepath, 0, "name"). Sorry for misdirection. Fixed my post and added a scene with working expressions.

Edited June 24, 2017 by f1480187

[tagosaku]

Oh, I am sorry too that I just knew there are TWO expressions, "prim" and "prims" !! I completely misunderstood them. Thank you, f1, so much for providing a sample file. I am checking it out right now!

[f1480187]

VEX allows to define two functions with same name returning different types, but HScript Expressions not. There is a string-returning alternative ended with s for functions where string result can be expected alongside with floats:

Common: chs, ifs, stamps
Attributes: points, prims, vertexs, details
Other: pythonexprs, evals, propertys, copmetas, dopfields, dopoptions, iprquerys

Edited June 24, 2017 by f1480187