Understanding Bones and Skeletons

Bone objects are common in 3D. They are typically used as a method to control the motion and position of a group of 3D points without having to move the points individually. Bones are not rendered; they are only included as guides to manipulate the character. Anime Studio uses bones in a similar manner to 3D packages, but there are some differences.

When many bones are combined together, they form a skeleton, which is hierarchically organized with parent and children bones. All bones are parented under a root bone that controls the entire character. While bones and skeletons are common in the 3D world, they can be scaled to the 2D world and are quite revolutionary.

All bones are included on a separate bone layer, which makes them easy to locate and manipulate. Bone layers, like group layers, can hold several sublayers.

Working with Hierarchies and Forward Kinematics (FK)

One of the key features of bones is their ability to be parented to other bone objects. By creating a hierarchy of bones, you can control all the bones in the skeleton by simply moving the root bone. The root bone is the bone that is at the top of the hierarchy, and it is the parent of all the other bones.

A parent bone can have several children attached to it so that moving the parent bone automatically causes the children to move with their parent. Children bones, however, can move without altering their parents. This allows a parent bone located at the shoulder, for example, to control the movement of all the rest of the arm bones, but the forearm bone can still move independently of the shoulder.

The ability of a parent bone to control its children bones is called forward kinematics, or FK for short. Using FK, Anime Studio can calculate the movement of children bones when the parent bone moves by using the connection between the two bones.

Drawing Objects to Be Used with Bones

Bones can be used to control layers and points. If a bone controls a layer, the rotation point for the layer is defined by the bone’s base point. Having a bone control an entire layer keeps the layer from being deformed as the bone moves.

However, if the bone is bound to a selection of points, then the way the vector object is drawn will determine how the object is distorted when the bones are moved. When drawing objects that will be controlled by bones, try to keep the curves smooth. Any sharp points located near the bone joint will be distorted when the bones are moved, which will cause the fill to overlap on itself.