Forums Technical Discussion Why do I have to add "@" before attribute name in Point Wrangle but not HDA

Why do I have to add "@" before attribute name in Point Wrangle but not HDA

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uuLLFA
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90 posts
Joined: May 2016
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Hello,

I'm wondering why is it that I have to add “@” before an attribute name (like @P) when using point wrangler but when doing a houdini digital assets?

point wrangle code: 

if (@P.z > 0) {
        @P.z = 0;
        @Cd = {0,0.5,0};
        
}

HDA code:

sop
vih_flatten_example()
{
if (P.z > 0) {
        P.z = 0;
        Cd = {0,0.5,0};
        
}
}
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AlbertoGZ
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Joined: Jan. 2017
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I'm a newbie in Houdini and VEX code, but in Wrangle documentation seems to explain it uses @ to create temporary VEX variables.

https://www.sidefx.com/docs/houdini15.0/nodes/sop/pointwrangle [sidefx.com]
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tamte
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8551 posts
Joined: July 2007
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@ is a special syntax for snippets to bind to an attribute
it's not part of VEX language
you can dive into Point Wrangle, RMB on attribvop1 inside and choose VEX/VOP Options/View VEX Code… to actually see the VEX code created from your snippet

more help on snippets here https://www.sidefx.com/docs/houdini15.5/vex/snippets [sidefx.com]

if you are building your operators directly in VEX, then certain types of operators already have some Global Variables that may be bound to or return certain data like SOP type operator you mentioned, however you can't just use the same logic for custom attributes, as well I'm not sure if P or Cd or other would just work like that for CVEX operators, you would need to define them as operator function arguments
Tomas Slancik
FX Supervisor
Method Studios, NY
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