1. Character Animation for Realtime Applications Michael Putz Klaus Hufnagl Institute of Computer Graphics Graz University of Technology Austria

2. 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

3. 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)

4. 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..

5. free download at http://www.bongfish.com

6. 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

7. 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.. )

8. 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)

9. 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)

10. SKELETAL ANIMATION vertices bound to hierachic bonestrukture quaternions used for „bones“ bone movement -> skin movement 1 matrix transformation -> 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

11. SKINNING / SOFT-SKINNING rigid: each vertex corresponds with only one bone -> bulges soft: (multiple weights) drawback: computation overhead

12. 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

13. 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?

14. 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

15. 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.

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

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