Edge Flows

Greetings and salutations! Today I am going to briefly cover my thoughts on how I plan on approaching the edge flow for the lo-res mesh for Aphrael. There are three areas I will highlight: the face, torso, and feet.

First, for anyone who doesn't know, edge flow is the flow of continuous edges of polygons around a particular shape. When they meet up in the same spot as the origin, it is known as an edge loop. How edge flow is approached is very important, especially for lo-res meshes because it can affect the shape of how the mesh will morph doing bending, stretching, and other things during animation. Since Aphrael will be rigged, I need to make sure that the edges flow around the mesh in a way that will minimize strange artifacts in the mesh and allow smooth morphing. Here are examples to illustrate my point:

Facial Edge Flow

The face is probably the most complex and most difficult part of the body to get the edge flow correct and smooth. Part of the problem is that everyone's face is different, hence the edge flow will be different for each person. However, this is where knowledge of anatomy comes into play. You see, the face is made up of several different muscle groups that all control how it morphs so we can generate expressions. Those muscles flow in a very specific way. For example, the muscles around the eyes form a loop around the eye sockets. The same happens with the mouth. For the cheeks, muscles flow straight down into the the mouth muscles, thus allowing us to smile. This is a simplistic explanation, but I hope everyone understands. In order to replicate facial expressions when animating, the modeler needs the edge loops to flow in the same direction as the muscles in the face. Hence my crazy drawing above. The large pink areas represent large polygonal areas that need to be considered as possible muscle groups for animating. The red arrows specify the flow those edge loops need to take, or at least an approximation. Now there is no right or wrong way to do it (well actually there is and that is by not using edge loops at all!) because everyone plans their edge loops differently and each face is unique. The whole goal is to minimize the mesh from breaking or morphing into strange artifacts and keeping the animations as natural and close to reality as possible. Even cartoon characters like in Pixar films follow this basic knowledge of edge loop flow, hence the animations are very smooth without the mesh breaking.

Now generally when I do the face, I kind of think of the face as a mask with one large edge loop flowing around the eyebrows and below the chin and jaw to define its border. Then I define all the other loops within that mask. All orifices have a loop around them to define their edges: the mouth, the eyes. and the nostrils. Secondary loops are then defined. For example, I place another loop around the tip of the nose and the nostrils and then a larger loop around the nostril wings, nose tip and nostrils to clearly define the nose. To help define laugh lines in the mesh if necessary, I then create an even bigger loop that goes around the bridge of the nose, encompassing the three smaller nose loops, around the mouth, and just beneath the chin. While I am creating these loops, I also have to think about the flow of edges that connect these different parts of the face. I use facial muscle groups as guides to define how those edges flow into the other loops, creating a nice cohesive whole that I believe will animate well when rigged.

For the rest of the body, it is far simpler on a lo-res mesh. For example, here is my plan for the torso:

Torso Edge Flow

The torso only really needs to be horizontal bands of edge loops. Sure, I could have the edge loops follow the direction of the clothing, but then the body wouldn't morph correctly. The detail in the clothes' form will actually be held in a normal map baked onto the lo-res mesh, so modeling that separately will not be necessary, hence why I sculpted first. The whole point is to mimic the correct way that the human body moves without breaking the mesh. Using horizontal bands on the torso will allow the body to morph in a far more natural way and it won't break the mesh. One of the things with edge flow is that it really is a bunch of judgment calls. You have to determine if the edge flow you are planning to create will work with how the character is going to bend and stretch in addition to how that edge flow relates to the rest of the body. If you are rigging a nude character for instance, then it probably is a good idea to follow some of the muscle flow underneath the skin so you can morph the muscles when the character flexes, relaxes, bends, etc. For clothes though, that may not be necessary.

Another example are the shoes that Aphrael is wearing. These are hard surfaces combined with an organic shape that are meant to bend so a different approach is needed.

Shoes Edge Flow

Since Aphrael has metal plates on her shoes, these need to actually be modeled appropriately. Usually when I do hard surfaces, I model the edge first. This allows me to define the shape from the outset so then when I am ready, I can just fill in the rest with simple polygons. For the feet, the plates need to be modeled with the flow of their edges in mind while still incorporating a horizontal like band pattern so that they bend correctly when the foot rolls during a walk or run cycle. Thus the edges can be modeled first and then the empty space can be filled with horizontal bands of polygons. Easy!

So that is how I plan on approaching the edge loops for Aphrael's lo-res mesh. Next time I post about Aphrael, I should have the lo-res mesh modeled and ready for UV mapping, so stay tuned!