UVs and SubDs: Raw! Uncensored! Also, Massive.

by akrid

I was pondering not showing what I've been doing this weekend, as it's truly hideous and not even close to a presentable state. In 3D, there are many artists who choose to obfuscate their abilities by only showing their best work. It's crazy how much polish I (and others) feel we need to put into WIP images, But I've come to the conclusion that If I'm to do a weekly blog I don't have that luxury. In other words, I'm not going to try and make you think I'm some kind of 3D God. Hopefully you understand that not every step in the process is a work of art.

Anyway, I think I can use this as an example to lay down some fundamentals I haven't talked about. It's kind of a long one, but there are plenty of pretty pictures to amuse you.

Ignore the splotchiness, It's caused by low GI settings. Keep in mind this is very much a work-in-progress.
This is what I've been working on this weekend... A sort of... Shop front? Hotel? I have no clue. I just started modelling and didn't stop till it was done. The project file for this is literally labelled "A thing". So lack of direction would be my first mistake here.
With a little more polish I think the front facade could work, but I think I'll have another go at the interior (And actually determine what sort of building this is supposed to be). I think I have a few things that work well in there (The marble, the wood desk), but overall it's not working. The exterior has a very clean almost surreal feeling, so maybe I can roll with that.
I really don't feel like I'm learning much from this project, nor do I think it's going to turn into something that great. The best I'm hoping for at this point is to make it into a decent filler portfolio piece.

Grade 3 Geometry Lesson

We good? Alright, just checking.

Sub-division Surfaces

6, 24, 96, and 384 polygons respectively.
A sub-division surface refers to a polygonal mesh that has had its polygons divided. Each polygon is divided into four. The position of each new vertice can be determined through different ways, but the most common method is devised by and referred to as Catmull-Clark.

Now, basically you can smooth out meshes. But it becomes interesting when you get in to sub-division surface smoothing (Or SDS).

An SDS cube.
SDS has the exact same outcome as that outlined above, but the difference is the new geometry is virtualized along the base mesh. You have no direct control over the new geometry, it merely interpolates within the polygons of your previous sub-division level. This proves useful in keeping you're geometry manageable and presentable, and yet smooth and deformable for animation purposes.

Subdivision Modelling

Now, finally what I've been trying to get at. Having a perfectly smooth and slick mesh is rarely what one wants. What if you want to throw in a few sharp edges and angles? Well you can, through the magic of control lines!

Above cube, with control lines highlighted.
Control lines refer to additional edges added solely for the purpose of controlling a subdivision surface. By limiting the range a polygon can smooth out to, you can create sharp and yet smooth edges very easily. No object in the real world has a perfectly sharp edge. There is always a certain radius to it. The SDS method mimics this fact, allowing you to create high resolution models with ease.

Counter bevel.
I can't really describe how to use control lines, it's really something you have to experiment with. And this little tangent is relevant for the fact that I used it on the marble countertop in the scene. SDS is pretty important for reflective objects. The reflectivity looks very weird on an unsmoothed mesh.

UV Mapping

Doubleshot! (This is the part where most of you will get bored and stop reading.)

UVs are an integral part of texturing. It's the magic ingredient that turns a 2D texture into 3D information. The name UV strangely comes from the the way the axes are labelled. The horizontal axis is U, Vertical is V.

It's best to think of UVing as a sort of reverse papercraft. Imagine you have an already built papercraft model, but it's entirely blank, so you want to de-construct the model back down into it's original flat form in order to draw on it. That's UV mapping in a nutshell! Just replace the paper with polygons, and the colored pencils with a .jpeg.

I have a simple example of a use of UVs with the red window in this scene. Instead of making a specific texture to fit around the geometry, using UVs I'll make the geometry fit around the texture. I have a texture that has the grain of the wood heading in a vertical direction:

I flatten a kind of copy of the geometry out into a 2D form. This is what determines how the texture is applied to the geometry. The texture underneath the polygon is the texture being applied to it.

But the problem is if I apply this texture as is to the window, all the pieces will have a uniform vertical grain, which looks pretty bad. In any sort of wood construction, the grain of the wood always follows the longest dimension of the piece.

The grain over ^here should be heading this way