1. Computer Animation Ying Zhu Georgia State University
Character Animation with Armature

2. Skeletal animation
Skeletal animation is the standard way to animate characters
A character is represented in two parts
A polygon mesh model of the character (called skin)
A set of bones (called skeleton, or armature) used for animation

3. Armature
“An armature is the name of the kinematic chains used in computer animation to simulate the motions of virtual human or animal characters.” – Wikipedia
In character animation, directly animating the polygon mesh is too time consuming.
Instead, you attach the polygon mesh to an armature.
Then you animate the armature, which in turn animates the polygon mesh model.

4. Benefits and drawbacks
Benefits of skeletal animation
Reduce the number of moving parts that an animator needs to control
Can build hierarchical skeletal structures
Can apply inverse kinematic techniques to make an animator’s job easier
Weaknesses
Cannot simulate realistic muscle or skin motion

5. Rigging and skinning
Rigging: the process of building a hierarchical set of bones for animation
Skinning: the process of attaching polygon meshes appropriately to the bones

6. How to add armature?
In Object mode, press Space bar and add an armature
How to extend a bone?
Select a bone, enter Edit mode. Select tip of the bone, press E or ctrl + LMB to extrude bones
Each extruded bone will be the child of the previously selected bone
This way you can build a hierarchical skeleton model

7. Different representations
Select armature, in Editing panel, under “Armature”
Octahedron: useful for positioning and extending
Stick: slim, useful for weight painting
Envelope

8. Armature parameters
Select armature, in Editing panel, under “Armature”
X-Ray
Display bones in front of the polygon mesh
Usually you want to turn this on
X-Axis Mirror
Use Shift + E to symmetrically extrude bones
Names: draw bone names

9. Armature parameters
In Edit Mode, in Editing panel, under “Armature Bones” tab
BO: edit name of the bone
In this panel, you can also edit the parent/child relationship between bone
You can also press/unpress the “Con” button to change connections between bones
Useful for inverse kinematics (IK)

10. Naming convention Naming convention for symmetrical bones
Include word “left” (or l), “right” (or r) in the bone names
Separate the word “left” and “right” with other part of the bone name with a separator (dot ‘.’, dash ‘-’, underscore ‘_’, or space)
For example: arm.l, Left.hand, Foot-r, Righthand, etc.
Be consistent
This is required for convenient tools like X-Mirror weight painting

11. Armature Posing Select armature, enter Pose mode
RMB to select bones, then you can rotate, move, or scale bones

12. Skinning
Two methods:
(preferred) Apply an “armature” modifier to the polygon mesh
Make polygon mesh a child of armature

13. Skinning through modifier
Give your armature a meaningful name
By default it’s called “Armature”
Select the polygon mesh, add an “Armature” modifier
Type the Armature name in “Ob:” field
Usually un-press “Envelopes” button and keep “Vert.Groups” select to use Weight Paint
(Use Envelopes only for simple skinning)

14. Skinning through parenting
Select the mesh first, select the armature
Make sure you select all the bones you want to associate with the mesh
Press Ctrl + P
Make the polygon mesh a child of the armature
In subsequent menu “Create vertex groups?”
select “Create from bone heat” if you want to use Weight Paint
Select “Create from envelopes” for simple skinning
After this step, you can do weight painting

15. Weight paint
Weight paint is a technique for attaching polygons to each individual bone
Armature must be in “Pose” mode
Otherwise cannot select bones in the “Weight paint” mode
Select the polygon mesh, enter “Weight Paint” mode

16. Weight Paint
In weight paint mode, the color of the polygons indicate the influence (weight) of a bone on these polygons
Blue means zero influence (0)
Red means maximum influence (1.0)
Other color (e.g. green, yellow, or orange) means somewhere between 0.0 and 1.0.

17. Weight Paint
Select a bone to see which polygons are influenced by this bone
Initially the polygons are probably blue
Use paint brush to paint on the polygons in order to change the influence (weight) of the selected bone on the polygons
Only takes effect if you paint on vertices, not on faces
You’ll see the color of the polygons change

18. Weight Paint parameters
In Editing panel, under “Paint” tab
Weight: select the current influence level
Opacity: press on the brush
Size: size of the brush
Paint method: mix, add, sub, mul(tiply), etc.
All faces: turn on or off the brush circle
Spray: continuously apply paint pressure

19. Weight Paint parameters
In Editing panel, under “Paint” tab
X-Mirror: paint symmetrically if the bone names are symmetrical (this is why you should follow the naming convention)
Clear: clear all previous paint for the selected bone so you can start over (like a “undo all” button)

20. Posing in Weight Paint mode
There is usually no need to switch betwene Weight Paint and Pose mode
You can manipulate the bones in Weight Paint mode
When you move the bones, you may see some polygons are mistakenly attached (or not attached). Just paint over them

21. Edit mode
Note that a polygon mesh is not animated by the bones in Edit mode
If you select the polygon mesh and enter Edit mode, the mesh will go back to “rest” position
If you select bones and enter Edit mode, the bones will go back to “rest” position

22. Weight paint and vertex group
What weight paint essentially does is to create a vertex group for each bone.
You can see the vertex group associated with each bone in Edit mode
Select polygon mesh, enter Edit mode
Under “Link and Materials” tab, see “Vertex Groups” field
Select a bone by name, press “Select” button to see the vertex group for that bone

23. Weight paint and vertex group
You can add or remove polygons to/from each vertex group
Give more control to animators than just weight paint

24. Armature and Sub-surf modifiers
Usually the Armature modifier should be above the Sub-surf modifier in the modifier stack
This means the Armature will animate the base mesh first, and then Sub-surf will happen later

25. Inverse Kinematics
Inverse Kinematics (often called IK) is an important technique for character animation
When we place a hand or foot to a certain position, we want the rest of the arm/leg to follow the hand/foot.
IK means that when a child bone is moved, the parent bones are automatically moved to follow it.
On the other hand, forward kinematics means that only child bones will follow parent bones

26. How to add IK to armature?
Select a bone (usually the tip on a bone chain)
Enter Pose mode
Add a “IK Solver” constraint
The “IK Solver” constraint is only available in the Pose mode

27. IK parameters
Can change the “ChainLen” number to add/remove bones from the IK chain
By default, “ChainLen” is 0, which means all the bones that are connected with the selected bone are in the IK chain
You can also add a “Target” object so that the IK chain will track to the target object
E.g. catching a ball
You can make the IK chain Rot(ate) with the target
You can adjust the influence of IK on the bone chain

28. What is motion capture?
Motion capture involves measuring an object's position and orientation in physical space, then recording that information in a computer-usable form.
Objects of interest include human and non-human bodies, facial expressions, camera or light positions, and other elements in a scene.
In most instances, a live subject, most likely human (but possibly and animal or puppet), is used as the source of data which is transformed into another form.

29. Motion capture (MoCap)
MoCap is used extensively in films
But game industry accounts for 85-90% of the total MoCap usage
Almost all games use MoCap to drive character animation

30. Importing motion capture data
You can import motion capture data into Blender
As of 2009, Blender can import two MoCap file formats: BVH and C3D
Go to File  Import.
In case you don’t see the importing scripts, reinstall Blender.

31. Importing motion capture data
A MoCap file will be imported as an armature
You can then attach polygon mesh to it and do weight painting, etc.
But you can change the armature pose at any frame

32. MoCap data Lots of MoCap data online (many of them free)