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Animation

Animation. Low-Level behaviors Overview Keyframing Motion Capture Simulation. Low-Level Behaviors. Keyframing Motion Capture Simulation. Generating Motion. What matters? Quality of motion appropriate for rendering style and frame rate Controllable from UI Controllable from AI

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Animation

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  1. Animation Low-Level behaviors Overview Keyframing Motion Capture Simulation Game Design

  2. Low-Level Behaviors • Keyframing • Motion Capture • Simulation Game Design

  3. Generating Motion • What matters? • Quality of motion appropriate for rendering style and frame rate • Controllable from UI • Controllable from AI • Personality of the animated character Game Design

  4. Keyframe Example Game Design

  5. Keyframing • Fine level of control • Quality of motion depends on skill of animator Game Design

  6. Motion Capture • Natural-looking motion • Hard to generalize motions • Registration is difficult • “Weightless” according to professional animators Game Design

  7. Motion CaptureImages courtesy Microsoft Motion Capture Group Game Design

  8. Simulation (Broadly Defined) • Physics is hard to simulate • Pseudo-physics is somewhat hard • Control is very hard • Gives Generalization + Interactivity Desired Behavior Forces and Torques Model Numerical Integrator User/AI Control State Graphics Game Design

  9. When to Use What Method? • Keyframing • Sprites and other simple animations • Non-human characters • Coarse collision detection • Motion Capture • Human figures • Subtle motions, long motions • Simulation • Passive simulations • When interactivity w/ motion is important Game Design

  10. Keyframing Game Design

  11. Keyframing Game Design

  12. Keyframe Example Game Design

  13. Keyframing • Fine level of control • Quality of motion depends on skill of animator Game Design

  14. Hand Drawn Animation -- 2D • Sketches • Pencil tests • Inking • Coloring • Digitize to sprites Game Design

  15. Computer Animation: 2D or 3D • Sketches • Models and materials • Key configurations • Playback of motion or render to sprites Game Design

  16. The development process: Adjust trajectory Playback motion Parameters: Locations Joint angles Shape -- flexible objects Material properties Camera Motion Lighting Keyframing Game Design

  17. Keyframing Interpolation • Inbetweening v 1,2,3 4 5 6 7,8,9… Linear time v 1,2,3 4 5 6 7,8,9… Slow in, Slow out time Game Design

  18. Interpolation Example Game Design

  19. Key Frames 1 2 3 Game Design

  20. Key Frames • Timeline • 1 2 3 3 1 Game Design

  21. Inbetweening • Frame dependent (“wrong”) slow-in/out • Iterate once per frame • This is a variant on the Infinite Impulse Response (IIR) filter: Game Design

  22. Inbetweening • Frame-Independent (“right”) slow in/out • Compute acceleration a Time of last frame Time Tend Game Design

  23. Spline-driven Animation y x,y = Q(u) for u:[0,1] • Equal arc lengths • Equal spacing in u x Game Design

  24. Reparameterize Arc Length • S= A(u) = arc length • Reparam: • Find: Bisection search for a value of u where A(u) = S with a numerical evaluation of A(u) (Details in Watt & Watt) Game Design

  25. Keyframing -- Constraints • Joint limits • Position limits • Inverse kinematics Game Design

  26. Keyframing -- Constraints Game Design

  27. Coordinate Systems Game Design

  28. Kinematics • The study of motion without regard to the forces that cause it Draw graphics Specify fewer Degrees Of Freedom (DOF) More intuitive control of DOF Pull on hand Glue feet to ground Game Design

  29. Inverse Kinematics Game Design

  30. Inverse Kinematics Game Design

  31. What makes IK Hard? • Many DOF -- non-linear transcendental equations • Redundancies • Choose a solution that is “closest” to the current configuration • Move outermost links the most • Energy minimization • Minimum time Game Design

  32. IK Difficulties • Singularities • Equations are ill-conditioned near singularities • High state-space velocities for low Cartesian velocities • Goal of “Natural Looking” motion • Minimize jerk (3rd derivative) Game Design

  33. Motion Capture • What do we need to know? • X, Y, Z • Roll, Pitch, Yaw • Errors cause • Joints to come apart • Links grow/shrink • Bad contact points • Sampling Rate and Accuracy Game Design

  34. Motion Capture • Goals: • Realistic motion • Lots of different motions (300-1000) • Contact • Appropriate game genres • Sports • Fighting • Human characters Game Design

  35. Applications Movies, TV Video games Performance animation Game Design

  36. Game Design

  37. Game Design

  38. Plan out Shoots Carefully • Know needed actions (80-100 takes/day) • Bridges between actions • Speed of actions • Starting/ending positions • Hire the right actor • Watch for idiosyncrasies in motion • Good match in proportions Game Design

  39. Sensor Placement • Place markers carefully • Capture enough information • Watch for marker movement • Check data part way through shoot • Videotape everything! Game Design

  40. Game Design

  41. Technology • Numerous technologies • Record energy transfer • Light • Electromagnetism • Mechanical skeletons Game Design

  42. Technology • Passive reflection – Peak Performance Tech • Hand or semi-automatically digitized • Video • Time consuming • Issues • No glossy or reflective materials • Tight clothing • Marker occlusion by props • High frames/sec Game Design

  43. Technology • Passive reflection --Acclaim, Motion Analysis • Automatically digitized • 240Hz • Not real-time, Correspondence • 3+ markers/body part • 2+ cameras for 3D position data Game Design

  44. Technology • Vicon Motion Systems • Retroreflective paint on reflectors • Lights on camera • Very high contrast markers Game Design

  45. Technology • Active light sources -- Optotrak • Automatically digitized • 256 markers • 3500 marker/sec • Real-time • Specialized cameras Game Design

  46. Technology • Electromagnetic Transducers • Ascension Flock of Birds, etc • Polhemus Fastrak, etc • Limited range/resolution • Tethered (cables to box) • Metal in environment (treadmill, Rebar!) • No identification problem • 6DOF Realtime • 30-144 Hz 13-18 markers Game Design

  47. Technology • Exoskeleton + angle sensors • Analogous • Tethered • No identification problem • Realtime - 500Hz • No range limit - Fit • Rigid body approximation Game Design

  48. Dataglove Low accuracy Focused resolution Monkey High accuracy High data rate Not realistic motion No paid actor Technology Mechanical motion capture Game Design

  49. Technology • Technology issues • Resolution/range of motion • Calibration • Accuracy • Occlusion/Correspondence Game Design

  50. Animation Issues • Style • Scaling • Generalization Game Design

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