VEX and normals from @ptnum

[mottosso]

Hi all,

I'm new to VEX and am facing an odd issue. With an Attribute Wrangle iterating over points, connected with any polygonal mesh (in this case a Sphere).

// Why does this not work..
vector broken_normal = point(0, "N", @ptnum);

// Why this does?
vector working_normal = @N;

// And this as well?
vector working_position = point(0, "P", @ptnum);

if (@ptnum == 0) {
    printf("%s\n", broken_normal);
    printf("%s\n", working_normal);
}

// {0,0,0}
// {-6.31725e-09,7.5807e-08,-1}

As you can see, the "broken_normal" yields a value of { 0, 0, 0 } when I would have expected a value identical to the "working_normal". I'm running this on Houdini 18.

vex_and_normals.hipnc

[bunker]

Nothing weird there. Your sphere doesn't have normals, @N is creating them on the fly.
Have a look at your Geometry spreadsheet.

[mottosso]

That's it, thanks. I figured it must have been something obvious like that.

But that begs the question; what attributes are generated on the fly like this? More importantly, how do I generate attributes on the fly for anything other than geometry 0?

[animatrix]

Hi, I think N is the only magical syntax SESI added to wrangles. But you can't manipulate any input other than the first input (yet). In a theoretical version of Houdini, this will be supported, that's why SESI advises to use geoself() for now.

[mottosso]

Thanks @animatrix