Skeletal Animation

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Skeletal Animation

• Zebulon Evans
• CS536 Computer Graphics
• CSUSM

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What is Skeletal Animation?

• Skeletal animation is simply a system of bones
  and joints (the skeleton) that is used to deform
  a model.
• Also known as a bone system it is used to create
  skeletal animations.
• A skeletal animation consists of a skin mesh and
  an associated bone structure.
• Moving a bone will also move the corresponding
  vertices of the mesh. 
•  

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Why Skeletal Animation?

• Memory advantages over loading a mesh for each
  frame to do the animation. 
• Each character has a single model.
• Each move or animation done by the model is just
  a set of bone movements which move a subset of
  verticies in the model.
• Relative ease to add new behavior to your models
  as it would just be defining a new set of bone
  movements.

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How Does a Bone System Work?
Basic triangle illustration
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How Does a Bone System Work?
Add some anatomy with 4 joints and three bones
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How Does a Bone System Work?

• J1 is the base joint
• All other joints are children of J1
• What happens if J1 moves?
• What happens if J4 moves?

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How Does a Bone System Work?

• The object mesh (usually you can use a single
  mesh, but you can also use more than one)
• Use weighted vertices
• A skeleton for the mesh, composed by a hierarchy
  of
• Bones
• Joints
• You can also define the range of motion.

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How Does a Bone System Work?

• A mesh is connected with your skeleton
• Each vertex in the mesh is associated with at
  least one bone and assigned a weight
• The weight determines how much the bone movement
  affects the vertex
• Pre-calculate the positions of the bones (poses)
  and create an algorithm to calculate
  interpolation between movements.

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How Does a Bone System Work?

• Skinning is when you connect a mesh to a bone
  structure
• While applying the skin is where you assign the
  vertex weights for each bone.
• This can be done in many 3D modeling packages
  such as Blender.

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How Does a Bone System Work?

• Skinning is when you connect a mesh to a bone
  structure
• While applying the skin is where you assign the
  vertex weights for each bone.
• This can be done in many 3D modeling packages
  such as Blender.

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Animation with Forward Kinematics

• Positions of particular parts of the model at a
  specified time are calculated from the position
  and orientation of the object, together with any
  information on the joints of an articulated
  model.
• The motion of the model is defined directly by
  the animator.

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Animation with Inverse Kinematics

• In contrast to forward kinematic animation, where
  each movement for each component must be planned,
  only the starting and ending locations of the
  limb are necessary.
• In inverse kinematics the orientation of
  articulated parts is calculated from the desired
  position of certain points on the model.
• The key is the use of constraints
•  limitations of the articulations of joints
• finite physical loads and speeds at which they
  are able to operate

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References

• Basic Introductionhttp//nehe.gamedev.net/data/a
  rticles/article.asp?article03In-Depth Custom
  System
• http//gpwiki.org/index.php/OpenGLTutorialsBasic
  _Bones_SystemBlender Armature and Stride
  Boneshttp//youtube.com/watch?vBnqEy5BKtLcfeatu
  rerelatedAdding Armature in Blender
• http//www.youtube.com/watch?vbDOszVr1gIcfeature
  relatedFinal Product Animation with
  Boneshttp//www.youtube.com/watch?vpPD_i5lreI8
  featurerelatedForward Kinematic
  Animationhttp//en.wikipedia.org/wiki/Forward_ki
  nematic_animationInverse Kinematic
  Animationhttp//en.wikipedia.org/wiki/Inverse_ki
  nematic_animationBlender Character Animation
  Featureshttp//www.blender.org/development/relea
  se-logs/blender-240/
•