Character Animation for Realtime Applications

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Character Animation for Realtime Applications

• Michael Putz Klaus Hufnagl
• Institute of Computer GraphicsGraz University of
  TechnologyAustria

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STRUCTURE OF THIS PRESENTATION

• 1. introduction
• 2. an old fashioned way of animation
• 3. example implementation
• 4. outlook to a new technique
• 5. example implementation
• 6. diskussion

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THE OLD WAY

• low polygon alien character mesh (1200 polys)
• main character of a freeware game STOKEDRIDER
• currently under developement by a group of
  students
• animated using keyframes and mesh interpolation
  (also called vertex tweening)

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LINEAR MESH INTERPOLATION

• artist models keyframes in 3D Software
• export keyframes (vertex normal positions)
• runtime application generates missing
  interpolation-frames
• BUT NOW let us take you where the action is..

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free download at http//www.bongfish.com
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CONSTRAINTS OF MESHINTERPOLATION

• smooth animation
• folding-seams eliminated
• (but only within a certain range)
• fast
• - multiple copies of the mesh in memory
• (one for each key frame)
• - limit on the level of interactivity and realism
  
• - no dynamic animations at runtime

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SOME STATISTICS

• STOKEDRIDER filesize 7 MB
• keyframe meshes 21 2.3mb ( 32 of
  filesize)only 3 tricks animations, the rest is
  used for ground movement ( steering, switching
  direction etc.. )

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WHAT DO WE EXPECT FROM OUR NEXT ANIMATION-SYSTEM ?

• unlimited trick combinations for the alien rider
• response to enviromental stuff (collisions
  with objects, different ground conditions)
• fluid and physically correct movement
• should be a realtime implementation
• nextgen hardware should be supported
• (vertex shaders)

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THE NEW APPROACH

• 2 different animation systems!
• 1. OFFLINE ANIMATION(exported animation using a
  skeletal system and softskinning)
• 2. ONLINE ANIMATION(realtime deformation
  according to ingame physics)

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SKELETAL ANIMATION

• vertices bound to hierachic bonestrukture
• quaternions used for bones
• bone movement -gt skin movement
• 1 matrix transformation -gt many
  corresponding vertices
• no need to store vertex positions for all the
  vertices for every frame of the animation
• derive intermediate frames by using spherical
  interpolation
• smooth transitions while changing from one
  animation to the other
• the memory bandwidth is very small
• - close to joints deformations can result in
  creasing

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SKINNING / SOFT-SKINNING

• rigid each vertex corresponds with only one bone
  -gt bulges
• soft (multiple weights)
• drawback
• computation overhead

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OFFLINE ANIMATION

• premodelled in e.g. 3dsMax, Maya, Milkshape,
• some IK physik skeleton (like BIPED)
• use envelopes to set and correct weights
• generate animation-cycle (for the bones
  keyframes)
• exported filestructure consists of
• mesh container (lokale matritzen)
• hierachichic bones (FrameTransformMatrix)
• skin (texture UV-coordinates)
• list of weights
• animations

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ONLINE ANIMATION

• arm shake animation for the alien-character
• both arms should shake according to riding speed
• physics-engine generates animation parallel to
  offline animation
• BUT HOW TO COMBINE BOTH SYSTEMS?

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IMPLEMENTATION OF HANDSHAKING

• using the already existing bone-hierachy parsing
  code from offline animation
• wait for shoulder bone than modify all bones
  below using sin/cos depending on riding speed
• simple but effective without almost any cpu
  costs

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ONLINE ANIMATION

• lots of other uses for physic based animation
• Look-at constraints
• Secondary motion (Chest Heaves ,breathing)
• Inverse Kinematics
• Muscle Bulges
• Ponytails, clothes, belly etc.

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OUTLOOK

• more sophisticated online animations than sin/cos
• physic-based realtime IK
• using realtime terrain information gt realistic
  crashes
• enhanced motion blending of the animations
• support of multichannel precalculated animations
• complexe Offline Animation of details

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QUESTIONS ?
for in-depth information about the
implementation, please take a look at our paper
or visit http//www.bongfish.com/stokedrider