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reference materialAnimating with Bones
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What are bones?
As in the human skeleton, they underly the "skin" of the form. Move or rotate a bone and the skin moves in response. In animation, this feature will cause the form or "skin" around the bone to distort in response to the bones movement or rotation.

NOTE
For this purpose, it is important to have TRIANGULAR polygons OR subpatched polys comprising the objects/forms that will incorporate bones, to avoid non-planar rendering errors.

Bones function by first holding a default rest position and rest rotation. After this, anytime a bone is moved, rotated, or sized away from its rest settings, the object will deform. How much the object deforms is based on the number of bones, their ranges of influence, and their relative strengths. It helps to think of bones as magnets that attract parts of an object (those closest to the bone) as the bone is moved, rotated, or
sized away from its rest settings. Bones play against each other, so you usually need at least two. A single bone will affect every point within an object (unless an influence range is used).

NOTE
Because bones are generally set up in a hierarchy, they are often used with Inverse Kinematics.

NOTE
As with displacement and clip maps, bone information is saved as part of a scene file and not as part of an object. In order to load an object and its bones into a scene, use Load From Scene.

Steps to add bones one style
1. First, you need an object to add bones to, this object should have triangular faces.

2. Load object into scene.

3. With the object actively selected, under Items / Add / Bones / Add Bone.
You'll be prompted to name the bone. In the case of complex bone hierarchies it is wise and valuable to name the bones according to their function or placment within a form.

4. With bone selected as active object, rotate and move bone in to place.

5. Set the Rest Length of bone by selecting the Tool function and sizing the bone to fit the area of the object to influence. DO NOT USE the SIZE function.

6. Create key frame at frame 0 to establish these initial parameters.

7. Add all other bones, including child bones, and set into place at this time. It is much more effective to build the entire skeleton all at one time.

To add child bones, (two methods)
a. press "=" or
b. select child bone from the Add Bones pop-up menu, or

Child bones behave just as child objects do.

8. When finished adding bones and creating their key frames, make bones active by selecting each bone one at a time (two methods):
a. pressing "r" on the keyboard or
b. selecting each bone separately under Bone / Item Properties / and selecting the "Bone Active" box.


Steps to add bones another style
To draw a bone in a viewport:

1. In any Layout orthogonal-view viewport, select the object, or existing bone if you are drawing a child bone.

2. Select Items > Add > Bones > Draw Bones. (Since this is the initial bone, you can alternatively choose Draw Child Bones.)

3. Place your mousepointer where you want to place the base of the bone.

4. Drag your mouse to create the bone. To open the Bones panel: Select a bone and press the P key or click Item Properties.

NOTE
You can also borrow the bones from another object by selecting the lending object in the Use Bones From Object pop-up menu.


Activating and Deactivating Bones
Using the keyboard shortcut "r" activates the an selected bones. Multiple bones can be selected simultaeously. "CTRL+r" toggles between active and inactive status. The Bone Active option on the Bones Properties panel is also an option, though much more tedious to use regularly.
NOTE "activating" or "deactivating" bones does not reset their rest position.


Control of bones
How you control a bone's distortion of its assigned object's form is by one of two means:

Limiting the area of influence or Offsetting a bones influence by using other "control bones" to balance pull.


Limiting the area of influence
Under the bone properties menu, you can select "Limited Range." The default setting is unlimited. Once you select "Limited Range" you will be able to type in a minimum and maximum value/distance for each bone. Once "Limited Range" is set, you will see an outline around each bone in the Layout screen showing the maximum range (illustration 1A).


Offsetting bones
Offsetting bones is a method that simply pits one bone's unlimited influence against another. The points closest to the bones will react to the closest bone's movement.

This is the more intuitive and most would say the easiest method of applying a skeletal structure, even though it may seem the most vague. The only real tip for success using this method is to use "control bones" to help limit the amount of distortion. These "control bones" simply stay still but occupy space so that a portion of the form does not distort as the active bones are moved or rotated (illustration 1B).


Bone features
The following features can be found within the bone / item properties menu:

Joint Compensation
Limits the amount of distortion at the "joint" where bone meets bone for the current bone selected (illustration 2A-C).

Joint Compensation for Parent
Limits the amount of distortion at the "joint" where bone meets bone for the parent bone of the bone selected.

Muscle Flexing
Creates additional distortion in the shape of a bulge in the middle of the form as the bone is moved or rotated into a compressed state. It is generally more "realistic" for the parent of the moving bone to flex (illustration 3A).

Muscle Flexing for Parent
Creates additional distortion in the shape of a bulge in the middle of the form of the parent of the selected bone as it is moved or rotated. This is generally more "realistic" for the as a muscular flex (illustration 3B).


Setting the Rest Position
When you use the Record Bone Rest Position command, the rest current position and rotation values assume a "natural state" and are viewable as the Rest Position and Rest Direction values within the Bones panel. This creates a point of reference, so if you later move the bone (not the object), it can influence the object’s shape.

The Record Bone Rest Position command also activates the bone. If you need to reset the rest position, you may want to deactivate the bone before reapplying the Record Bone Rest Position command. Alternatively, you could manually edit the Rest Position and Rest Direction values.



See also Skelegons reference material.

illustration 1A - "Limited Range"
Note: the dotted capsule shape surrounding the bone is showing the "range" of influence established by the numeric settings.

illustration 1B - "Offset Bones"
Note: the polygons of this form are
displayed using the bounding box
mode to more easily demonstrate
what the bones look like.
     
     
     

Within the Layout, select Items / Add / Bones / Add Bone.
     
     
     
     
     
       
       
       
       
       
       
       
       
       
       
 
 
       
     
     

 

 

 

 
       
       
 

 

 
       
       
       
       
       
     

 

  

 

 


This object is used in all the examples below. Note the primitive characteristics and the subtle variations of form which are created by the deformation caused by the bone influence in each of the illustrations.
     
     

illustration 2A - "Joint Compensation 100%"

  

illustration 2B - "Joint Compensation 100%"
     
     

illustration 2C - "No Joint Compensation"

  

illustration 2D - "No Joint Compensation"
     
     
     
     
     

illustration 3A - "Flex 100%"

  

illustration 3B - "Parent Flex 100%"