Houdini VOPs Primer

A quick primer into using VOPs networks in Houdini.

Get the FREE Effects Demo Reel Guide here: http://www.nelsonlim.com/fxreelguide

Say hi on social:
IG: https://www.instagram.com/iamnelsonlim
FB: https://www.facebook.com/iamnelsonlim

Welcome to quick bites, a series where I drop really quick tidbits of information, tips, best practices, anything that I can squeeze really quickly into a video.

In today’s quick bite. We will be talking about VOPs. So what is VOPs? VOPs is a very easy visual way to manipulate Houdini attributes. I think a bit like visual scripting.

The easiest way to use VOPs is to drop an attribute VOP. Well, So let’s dive inside our attribute VOP by double clicking it inside. You will see a set of predefined attributes that are common attributes that you would find in Houdini, such as P for position, V for velocity, force, age, life, ID, color, UV, N normals. You’ll also find a bunch of outputs that are pretty common.

Again, position, velocity, color, normals.

So VOPs will perform its operations over discrete geometry types. In this case, it is going to run each operation over points, but you can use it to run over vertices or primitives or even detail. The idea being that each point will bring in a couple of attributes. At least it will bring in the position. You can perform some sort of operation in between. And finally, you can output that final position to the VOP output note.

So one of my favorite use cases, for VOPs is to deal with noise. I just find it easier than dealing with noise functions in VEX.

Let’s drop an anti-alias noise node, and we can sample the noise at the same position of our point coming in. And let’s ensure that it outputs a spatial, three dimensional noise output.

Let’s add that to the position. So by adding it to the position, we will now add noise to our current position and you can see the result is immediate.

If we prefer, we could also pipe our output, not to position, but to color. And you can see a three dimensional color. If you change this 3d noise now to 1D noise, you would see that it is a color from zero to one.

Now it can be a pain to have to dive into the VOP node each time to manipulate, for example, frequency or amplitude of noise. So it’s a very common thing to maybe middle mouse, click frequency and say promote parameter. And maybe we want to promote the amplitude.

Now, if we jump up by hitting ‘u’, we can now see that frequency is on the VOP attribute node itself, and we can manipulate our frequency to be much higher and even increase our amplitude.

If your attribute that you need to bring in is a custom attribute. You can always use the bind node to bring in your custom attribute, name it, whatever custom attribute it is, change it to whatever custom attribute type that you’re using. Pipe it into your noise or whatever operation you have. And if what you need to output is also a custom attribute.

You can use the bind export to finally export your own custom attribute and name it accordingly, as well as the correct type.

Finally, if you are interested in manipulating volumes with a VOP note, there is also a volume VOP node that you can use that will essentially do the same as an attribute VOP, but perform operations on a volume.

All right, this is the 20% you need to know in order to do 80% of the work in VOPs I hope you liked this quick bite series. And if you do, please like the video as well as hit subscribe and the bell to be notified when new content on this channel comes up, I’ll see you in the next video.