Describes: bones purpose, setting up a bone structure, animating boned objects.
One key tool for realistic character animation is the skeletal system, commonly referred to as "bones". Bones act just like human bones do, providing a support structure for a continuous polygonal "skin" that can bend and twist realistically. This is very different both from animating separate pieces (where the seam between them ruins the effect) and from creating geometric morphing poses: geometric morphings make points move along mathemati cal trajectories, while bones firmly tie points to the support structure making the animator's life easier.
Bones are commonly thought as difficult to set up and use, but this is not really true. The most difficult part is to create models that can be animated with bones: building a seamless human body is no small task.
For this tutorial we'll use a ready made object, just load the "skelhand.tor" object from the objects directory, or rebuild it as an exercise in beveling and metameshing: starting with a cube it can be built in a few minutes.
The object has been built to demonstrate key features of objects to be boned: it has extra detail at the joints so that polygons can be bent correctly by the bone system.
Placement of bones as seen in front view
With Objects> Skeleton> Add bone, add a bone to the workspace. Select it, and move it near the joint between the first finger and the hand. The bone is now pointing to wards +Z and is really small compared to the object's size, so scale and rotate it until it looks like the lower bone in figure.
A bone acts only on the points that are inside its radius of influence. The term radius here is used loosely, since a bone is really a line that extends along the Z axis. Every point that is placed X axis size units from the bone's Z axis is assumed to be grabbed by the bone. The grabbing intensity can also be controlled with the Bones Panel, but the primary method for setting up bones is to scale them in the editor.
Now copy and paste this bone, displacing it and scaling along its Local Z axis to cover the shorter articula tion. It is very important that bone segments begin where their parent bones end because when two bones are near they average their influence. A look at figure will explain how points are affected by those two bones.
How bones influence mesh points
In order to associate the two bones with the mesh, it is necessary to group them as children of the mesh itself. Select the hand, then the lower bone and group them. Deselect all with spacebar, select the lower bone and then the topmost one, grouping them as well. Now the hierar chy is defined. Save the project to disk and proceed with freezing.
Freezing bones with Objects> Skeleton> Freeze Bones (the mesh must be selected) analyzes the object and the bones and assigns the points of influence. It is mandatory to freeze bones before anything useful can be done with them.
Once bones are frozen the project must always be saved in Modeling mode with the bones placed where they were when frozen! Expert animators may make use of this feature to slightly modify a boned object and im prove their animations, but otherwise be careful!
Once frozen, the bones can be rotated and moved as any linked object but they will apply their changes to the original mesh as well. If the Update Bones checkmark in Workspace> Settings panel is active, the changes will be reflected in real-time to the mesh, otherwise an explicit Update Bones command is needed to see the change take place.
Side view of rotated bones and the resulting deformed mesh