1 More Animation and (maybe) Particle Systems Procedural Animation Motion Capture . Particle Systems Intro Differential Equation Basics Particle Systems Procedural Animation Motion Capture . Particle Systems Intro Differential Equation Basics Particle Systems Types of Animation • Keyframing • Procedural Animation • Motion Capture
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More Animation and (maybe) Particle Systems
Procedural AnimationMotion Capture.Particle Systems IntroDifferential Equation BasicsParticle Systems
Procedural AnimationMotion Capture.Particle Systems IntroDifferential Equation BasicsParticle Systems
Types of Animation• Keyframing• Procedural Animation• Motion Capture
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Procedural Animation
• Define the motion using formulas
–Hand-crafted
–Physically based
• The animator must be a programmer
• Keyframing starts to become procedural as expressions are added
• At some level of complexity it becomes easier/more efficient than keyframing.
Procedural Animation
Battle of Helm’s Deep, LOTR
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Procedural Animation
NYU Media Research Lab (Ken Perlin, Athomas Goldberg)
Dynamics
• Generate motion by specifying mass and force, apply physical laws (e.g., Newton’s laws)
• Simulates physical phenomena–gravity–momentum (inertia)–muscle forces
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Active Simulations
Active Simulations: Examples
Wayne Wooten, Pixar (by way of Georgia Tech)
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Active Simulations: More Examples
Petros Faloutsos, UCLA
Robotics Comparison
HRP2 robot, AIST (Japan)
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Performance-based Animation (Motion Capture)• Record the animation from live action
– simplest method - rotoscope (trace) over video of real motions
• Real time input devices
– electronic puppeteering
• Motion capture
– track motion of reference points » body or face or hands
– magnetic
– optical
– exoskeletons
– convert to joint angles (not always straightforward)
– use these angles to drive an articulated 3-D model
– These motion paths can be warped
Motion Capture
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Motion Capture Research
Motion Data AcquisitionMotion Data Acquisition
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Maze - Sketch InterfaceMaze - Sketch Interface
Re-sequenceRe-sequence
Motion Capture Region Virtual Environment
Obstacles
Sketched path
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Re-sequenceRe-sequence
Motion Capture Region Virtual Environment
Data AcquisitionData Acquisition
“Poles and Holes” rough terrain“Poles and Holes” rough terrain
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Terrain NavigationTerrain Navigation
Choice InterfaceChoice Interface
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Another Example
Arikan et al., (Berkeley)SIGGRAPH ‘03
Particle Systems
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References• W. T. Reeves, Particle Systems - a Technique for Modeling a Class of
Fuzzy Objects, ACM Transactions on Graphics, 2(2), pp. 91-108, 1983.– http://portal.acm.org/citation.cfm?id=357320&dl=ACM&coll=portal&CFID=12858257&CFTOKEN=79986367
• Karl Sims, Particle animation and rendering using data parallel computation, ACM SIGGRAPH Computer Graphics, v.24 n.4, p.405-413, Aug. 1990
– http://portal.acm.org/citation.cfm?id=97923&dl=ACM&coll=portal&CFID=12858257&CFTOKEN=79986367
• A. Witkin, D. Baraff, M. Kass: Physically-Based Modeling, SIGGRAPH tutorial course notes. 2001
– http://www.pixar.com/companyinfo/research/pbm2001/
• Partial slide credit: Thomas Funkhouser
Kinematics and Dynamics• Kinematics
– Considers only motion
– Determined by positions, velocities, accelerations
• Dynamics
– Considers underlying forces
– Compute motion from initial conditions and physics
• Today: Passive Dynamics:
– No muscles or motors
– Examples:» Smoke» Water» Cloth
» Fire» Fireworks
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Karl Sims, Particle Dreams
Particle Systems
CloudsSmokeFireWaterfallsFireworks
Reeves ’83, the Wrath of KhanBatman Returns, using Reynold’s flocking algorithms
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Particle Systems• For each frame:
– Create new particles and assign attributes– Delete any expired particles– Update particles based on attributes and physics– Render particles
Creating/Deleting Particles• Where to create particles?
– Around some center – Along some path– Surface of shape– Where particle density is low
• When to delete particles?– Where particle density is high– Life span– Random
This is where user controls animation
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Example: Wrath of Khan
Reeves
Example: Wrath of Khan
Reeves
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Example: Wrath of Khan
Reeves
Particle System Attributes• Creation—number, initial condiions
• position/velocity • randomness• surface of emitter shape • vertex of polygonal object
• size• color• transparency• shape• lifetime
• Deletion• Update of position/velocity
• translation• vortex
• Rendering style – motion blur, compositing
What control handlesdo we want/need?
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Equations of Motion: Gravity Only!
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Integration: accuracy improves as step size decreasesbut never a perfect match
Particle System Forces
• Force fields– Gravity, wind, pressure
• Viscosity/damping– Liquids, drag
• Collisions– Environment– Other particles
• Other particles– Springs between neighboring particles (mesh)– Useful for cloth
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Spring-Mass Systems
Cloth in 2DJello in 3D
Spring-Mass Systems
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Cloth
Increased Resolution of Mesh+Possible Shapes+ Smoothness- Simulation time
Breen ‘95
Modeling for Clothing
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Collisions for Clothing
Potentially VERY expensiveBounding Box Hierarchy
Partition space or objectsAvoid expensive primitive tests
Polygons Primitive Level
IntermediateLevel(s)
Top Level
Leaves in the Wind…
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Leaves in the Wind…
uniform sink source vortex
Add together to make interesting fields…
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Wejchert&Haumann, ‘91
The Challenges of Passive Simulation
• Accurate for the situation• What pieces of the physics are
necessary for appearance?• How to give the animator control?
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Dynamics, more generally• Point mass• Spring/mass systems• Linkages of rigid bodies• Other physical phenomena
–Aerodynamics–Fluids–Fracture–Explosions
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