VEX 101 and new point SOP

[Isleofgough]

A lot of old tutorials use the old point SOP for a color ramp, purely to assign a number between 0 and 1 for some future purpose. For instance for a line oriented along the y axis, the old point SOP has the color channels deleted and then puts an "add color" of ($BBY,0,0). Sometimes normals are deleted as well. Commonly the next node added is an attribute VOP with a ramp parameter to reassign this 0-1 range on the red channel to some  spline ramp value.

I am trying to not use the old point SOP for new models. I see there are two different nodes, and I am not sure which to substitute: the "point wrangle" with yellow cowboy hat (attribute wrangle) and the new "point" with red cowboy hat (attribute expression). Which is better to use? With the point wrangle, I can put in VEX code like "@Cd = set(.5, 1, 0);" to assign a constant color, but what would be the equivalent of $BBY? What is the VEX equivalent of the old point SOP "no normal" to delete normals? Thanks.

 

Edited December 12, 2017 by Isleofgough

[mestela]

$BBY equivalent as per your post:

vector bb = relpointbbox(0,@P);
@Cd = set(bb.y,0,0);

You can't delete attributes in a wrangle, you'd use an attribute delete sop.

It's all more verbose than before, but scales much better, and is more internally consistent. 

[Isleofgough]

Thank you. That is very helpful and works perfectly! A lot of tutorials are for older versions of Houdini, and some of the newer nodes appear to be completely different from the older versions: most notably the new and old point SOP. It looks like it would be better to learn VEX than python for Houdini work. I am somewhat familiar with older programs (Algol, Fortran C++, Visual basic, etc.) but have no experience with VEX. Your code will be very helpful for substituting a point wrangle (and a attribute delete) for the old point SOP.

[mestela]

Definitely vex over python when starting; python is handy for pipeline stuff, interfacing to other apps, best to delay that until you need it.

Usual plug for my wiki notes here:

http://www.tokeru.com/cgwiki/?title=HoudiniVex

 

[caspgin]

I have a question regarding this topic. Initially, I had normals pointing in the x-direction as shown in the image. I wanted to make normal and point away from the surface so I used the old point sop and just did no normal and reversed it. That worked as shown in the second image. What I want to know is what does the no normal option does in the background to make the normals proper (like does it add something )? How can I use the VEX expression to get the same result without the old point sop just using the attribute expression?

 

Thank you.

[Isleofgough]

Did you try an attribute delete node? I don't have access to a computer this week, but I would think that would work.

[caspgin]

Isleofgough Yes, I tried it now. Attribute delete works too. So is the old point sop deleting normal attribute when we select the no normal option in it? How can I replicate it in attribute expression?

[Isleofgough]

I don't think you can use attribute expression to delete an attribute.