A developer of visual media will often benefit from the ability to include 3D assets or animation. From videogames to videos, 3D animation is frequently used in the visual media industry. Even 2D games will frequently use 3D rendered sequences for sprites, cut scenes and animations. Whether you are a professional or a hobbyist, it is worth your time to learn at least the foundations of 3D animation so that you can understand at least what is available to use, even if you don’t have to create the 3D assets yourself.
There are many steps to creating 3D assets but the foundation is modeling. Modeling means creating the geometry of the 3D asset. This can be done in a variety of software, such as Maya, 3D Studio Max, Houdini, Blender, ZBrush and many others. Some software, like ZBrush, allow you to simply sculpt without the need to worry about edge loops or polygons. However, we will examine the type of 3D modeling where you have direct control over the position of edges and vertices. This type of modeling is called polygonal (or poly) modeling. I will use Maya as the software of reference, but the same principles apply to software like 3D Studio Max and others.
Whether you are creating an object or a character, 3D modeling involves creating a mesh that is the “skin” of the object. The mesh is composed of polygons, or “polys”. A poly is a face surrounded by edges. A poly surrounded by three edges looks like a triangle, and is called a “tri”. A poly surrounded by four edges is called a “quad”. A poly can have many edges, but as you will soon learn, this is considered poor practice.
Each point on a poly is called a vertex. In Maya, by default, polys are one-sided. That means they have one face, and are visible only from one side. Every poly has a “normal”, which is a vector perpendicular to the face of the poly, pointing in the direction of the face. You can toggle the visibility of the normal on and off. It is a good practice to check your normals, to make sure that all of the polys are facing outward. Now, let’s take a look at some other tips to better 3D modeling:
1. USE QUADS
If your 3D model is deformable or if it will be smoothed (subdivided), quads are the preferred method of modeling. Deformable models such as creatures or characters require a flexible “skin”. If you bend your elbow, for example, your skin changes shape and adjusts to fit the new position. On the other hand, a robot uses a mechanical joint to rotate an elbow, and often doesn’t have “skin” that would flex or bend. However, if it uses some kind of flexible cover over the joint, then that too would be considered a deformable mesh.
If the 3D object is stationary or non-deformable, using quads and tris is acceptable. However, quads can easily be divided using the smoothing function, without creating “poles”. Tris, on the other hand, tend to create “poles” which persist through subsequent iterations of division, and lead to sharp points that don’t smooth properly. Also, tris end edge loops, which are important to proper deformation and will be mentioned later on in this article.
All of your geometry should be either quads or tris, no other polys should ever be present in a finished model. If you have a poly with more than 4 sides, divide it. Some applications require all quads, or all tris, and sometimes you can use tris judiciously in an otherwise all quad geometry, but you should absolutely never have polys that have more than 4 edges.
There are various techniques to reduce edge loops, which you can use when you’re going from a high density edge loop area to a low density area. Research and experience will teach you how to handle virtually any situation.
2. CHAMFER EDGES
A note about sharp edges is that almost every object in real life has at least some roundness to its edges. Unless you’re talking about the edge of a knife or a sheet of paper, most edges which we consider sharp have at least a little bit of chamfer to them. Take a look at your desk, for example. The edges of furniture appear sharp, but upon closer inspection we notice that in fact they are rounded or flattened, to a minute amount. This amount is important to how light bounces off the edge.
Unless your model is a low poly model for a game, you should always take care to round edges appropriately. Even for low poly models, they often use normal maps generated from high poly versions which do have the nicely rounded edges that result in beautiful specular highlights when rendered. I can often tell the difference between a professional 3D model versus an amateur one, just by seeing whether the artist took the time to polish the model by rounding edges. It’s well worth the extra effort!
3. PROXY MODEL FOR SMOOTH RESULTS
Proxy modeling is a tool available in Maya and some other 3D modeling software. It allows you to model a low-poly “cage”, and simultaneously create a high-poly smoothed model. Usually, the cage is transparent, so that you can see the high-poly geometry inside. You also have the option to move the cage and model next to the high-poly version.
Proxy modeling is great for creating organic models such as characters and creatures. You can also create objects and architecture, simply by placing edge loops very close together to create “hard” edges. The nice thing about proxy modeling is that it will automatically smooth your model and that you can select the level of subdivision, seeing both the low-poly cage and high-poly model at the same time. Any changes applied to the low-poly cage will be immediately reflected in the high-poly model, and so you can manipulate the shape easily by pulling and pushing a few vertices. You have the benefit of both low-poly vertex-level control, and the ability to quickly and easily generate and modify a smooth high-poly surface without having to deal with too many vertices. If you do want to control individual vertices on the high-poly version, you can always break the connection to the low-poly mesh and sculpt away to your heart’s content!
Proxy modeling makes it easy to ensure your model has good geometry and good edge loops. I highly recommend using it.
4. CHECK YOUR HARD EDGES
Every polygonal 3D object, regardless of how round or smooth, is made up of polygonal faces. To give the appearance of a smooth curve, we must use many small faces. Let’s look at a sphere, for example. As a polygonal object, it is divided into many small facets, like a disco ball. The smaller the faces, the more round the sphere.
In 3D, we can choose edges to be hard or soft. If we make all the edges of the poly sphere hard, it will have a faceted appearance. If we soften the edges, it will look round and smooth.
Depending on what you are modeling, you may choose some edges to be smooth and others hard. It is important to “turn on hard edges” to check your work, before you submit the finished model, to make sure that the correct edges have been softened or hardened. If you skip this step, you will often find unexpected “creases” in your render, and may wonder how they got there.
In Maya, there’s a function that allows you to soften all edges below a certain threshold, for example 30 degrees. This is a good start, but you still need to check the edges after you apply this function to make sure there are no surprises.
5. PLACE EDGE LOOPS INTELLIGENTLY
Especially on deformable meshes, such as characters or creatures, proper edge loop placement is extremely important. Think about how a mesh will bend or deform, and make sure your edge loops run topologically perpendicular and parallel to the vector of movement. If your edge loops are diagonal to the deformation, you will see a lot of ugly deformation where edge loops are bent across topology.
The area to be extra careful about is the face. The eyes and the mouth should have edge loops in concentric circles, the cheeks should be able to contract naturally, the forehead and the nose should be able to wrinkle. There are many good books available on the art of 3D facial animation, but I recommend “Stop Staring: Facial Modeling and Animation Done Right” by Jason Osipa. This topic certainly deserves much more attention than I can give it in a short article, but I do want to bring up the importance of intelligent edge loop placement, because it will save you a lot of headache in the animation phase.
There are many, many tips, tricks and techniques that will help you improve your 3D modeling skills. Experience, books, online tutorials and forums are excellent resources. If you are artistic, love to create, or simply want to try a new art form, I encourage you to try 3D modeling. In my opinion, it is the art form of the digital age: it allows me to share my visions with the world, to create anything I imagine from virtually nothing, and to breathe life into it. Where in the past, visual art was often limited to a still image or sculpture, today we can incorporate movement, defy physics, and create illusions so realistic that they are virtually indistinguishable from real life! Don’t be afraid to try this new art form, it may give you the tools to fully express your creativity and unlock your inner child.
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