From the course: Houdini Essential Training

Object vs. suface context - Houdini Tutorial

From the course: Houdini Essential Training

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Object vs. suface context

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- [Narrator] When we're working with geometry in Houdini, there's a few different contexts and a few different names for things. And the purpose for this video is just to lay down those fundamentals so all of this is super clear. So what we're going to do is we're just going to make a torus in our default scene here off the shelf. So let me hit torus, drop that in the scene, and there we go. I can almost click the little cursor here to get rid of the manipulator. And I'll bring the torus object down here. I'm going to hit the P key, and I'm going to make it zero, one, zero. Actually, let's make it negative one. Okay, now I'm going to rotate it on the X 45 degrees and I'm going to scale it up three units. Okay, just so we can see it, and we have a torus there in our scene. Okay, so at this level here, we're just in our object level. And we see this node here got created automatically for us. And you can see that is a geometry node. And now, we haven't done this before, but I'm going to middle mouse click. And now we can start to see some other information about our object, and we'll use this a lot too just to be able to view different things about our node. And number one, we can see what level we're at. We're at /object/ and that's our torus_object. And what is this? This is a geometry object. So any geometry we create will be in one of these objects. And now we can move things around, for example, at two levels. I can control its rotation, scaling, translation, those kinds of basic transforms at this level. I can't do any deformation or manipulation of the geometry itself. That happens inside this node. So at this top level here, we do basic translates, rotations, scales. Inside here is where we actually build the geometry, edit it, manipulate it, deform it, all that stuff. So, this is sort of more a simpler top level node. And anything inside of it is handled separately. Alright, so now what I'm going to do is I'm going to go inside this torus object. And we see this one object got created, and this is the torus itself. If I middle mouse click, you can see first we see our path. We're at obj/torus_object1/torus. And now, this is the important thing I want to point out here. Now you see this is a Torus Sop. And this goes back to sort of the under-the-hood Houdini nomenclature about what these nodes are. At this level, it says Geometry here. What a sop is is a surface operator. And everything within the geometry context is going to be a sop that we're dealing with. And so, I'm going to use the terms sops which means surface operators which is everything happening in this context where we're actually building and editing geometry. And this is the only thing within the torus object that makes the torus. Like for example, let me select this. I'm going to delete it out. I'm going to go up a level. Our torus object is still there. This kind of container of geometry is still there. We could put anything inside of it. If I go inside, now I'm going to hit Tab which helps me make a new node. I'm going to type S P H and get a sphere and lay that sphere down. And I'm going to hit the U key to go back up. Now, this is still a torus object, again, because this is just a geometry container. It's dumb, essentially. It doesn't know what's inside of it. And all of these transforms, rotations, and scales still apply. We can see this is rotated towards us a little bit. It's been scaled up. And inside, we just deleted the torus out and we made a sphere. If I middle mouse click on the sphere, now you can see obj/torus_object. Now, this is a sphere1, and this is a Sphere Sop, a sphere surface operator. So now for example, in this, I'm going to change this to polygon from primitive. So now we actually have polygon faces on that. And now, we could go about editing different faces and manipulating all sorts of different things on this level and then control its overall position, transforms, and rotations at its top geometry level. Alright, so that's the sort of two worlds of geometry we're living in. We've got these higher levels where we could move things around and do sort of the more positional and basic manipulation of geometry. And inside these geometry nodes are our sops. And this is the huge playground where we'll start getting into where we can actually model, manipulate, do all sorts of things within the sop context of Houdini.

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