PhysicallyBased Modeling Generic Library

1
Physically-Based Modeling Generic Library

• David Brown Shawna Thomas
• 12/2/04

2
Physically Based Modeling

• Techniques that use physics to create realistic
  animations automatically

3
Library Hierarchy
Modeling System
4
Outline

• Basic Simulation Concepts
• Particle System Concepts and Example
• Flocking System Concepts and Example
• Mass Spring System Example
• Conclusion

5
Outline

• Basic Simulation Concepts
• Particle System Concepts and Example
• Flocking System Concepts and Example
• Mass Spring System Example
• Conclusion

6
Basic Simulation Concepts

• Modeling System
• Contains a set of modeling elements
• Encapsulates the motion in the animation
• Particle system, rigid body system, fluid flow,
• Modeling Element
• Contains a static portion and a dynamic portion
  (called state)
• Evolve over time by responding to forces through
  Newtons law Fma
• Particle, rigid body, fluid element,

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Basic Simulation Concepts

• Environment
• Set of obstacles that the modeling system
  interacts with
• Playground, room,
• (Environment.h)
• Obstacle
• Object that modeling elements interact with
• Sphere, triangle,
• (BasicObstacle.h, SphereObstacle.h,
  TriangleObstacle.h)

8
Basic Simulation Concepts

• Force
• Models the physical laws governing motion
• Applies an acceleration to a modeling element
• Gravity, wind, friction, collision,
• (Forces.h)

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Basic Simulation Concepts

• Numerical Integrator
• Mathematical tool to advance the modeling system
  to the next timestep given the modeling systems
  current state
• Euler, Midpoint, Runga-Kutta4,
• (NumericalIntegrators.h)

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Basic Simulation Concepts

• Simulation Loop
• Continuous loop where the modeling system is
  advanced through time based on the forces present
• while 1 do
• Reset modeling system
• Set A for each modeling element in the modeling
  system based on F
• Integrate the modeling system forward 1
  timestep
• Handle collisions
• Display to screen

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Outline

• Basic Simulation Concepts
• Particle System Concepts and Example
• Flocking System Concepts and Example
• Mass Spring System Example
• Conclusion

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Particle System
Genesis Effect from Star Trek II The Wrath of
Kahnby William Reeves
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Particle System
Particle Dreamsby Karl Sims
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Particle System

• BasicParticleSystemltTgt
• BasicParticleltTgt
• BasicState
• default_update_visitor

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Particle System

• BasicParticleSystemltTgt
• Models Modeling System
• Contains a set of interacting particles of type T
• Defined in Basic ParticleSystem.h
• Data Members
• vectorltTgt particles
• Double mass
• Methods
• UpdatetoNextTimeStep(UpdateVisitor vis)
• CheckCollision()

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Particle System

• BasicParticleltTgt
• Models Modeling Element
• Defined in BasicParticle.h
• Data Members
• double mass
• BasicObstacle collision
• T state
• Vector3d Color

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Particle System

• BasicState
• Models State
• Defined in BasicState.h
• Data Members
• Vector3d X
• Vector3d V
• Vector3d A
• Vector3d deltaX
• Vector3d deltaV

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Particle System

• default_update_visitor
• Used in UpdatetoNextTimeStep() to prep the
  modeling elements for the next simulation
  iteration
• template ltclass ModelingElementgt bool
  checkElement(const ModelingElement e)
• template ltclass ModelingElementgt bool
  updateElement(ModelingElement e)

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Transient Particle System

• TransientParticleSystemltTgt
• Refines BasicParticleSystemltTgt
• Particles are generated and killed during
  simulation
• Defined in TransientParticleSystem.h
• TransientParticleltTgt
• Refines BasicParticleltTgt
• Particle with a lifespan and a flag alive
• Defined in TransientParticle.h

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Transient Particle System

• transient_update_visitor
• Refines default_update_visitor
• Only updates particles that are alive
• updateElement()
• decrements lifespan by 1
• if lifespan lt 0, sets alive to false
• Defined in TransientParticleSystem.h

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Particle System

• Demo

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Volcano Simulation

• VolcanoState
• Refines BasicState
• Vector3d Tail
• VolcanoParticleSystem
• Refines TransientParticleSystemlt TransientPartic
  leltVolcanoStategt gt
• AdjustColor()
• volcano_update_visitor
• Refines transient_update_visitor
• updateElement() sets Tail to previous X position

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Outline

• Basic Simulation Concepts
• Particle System Concepts and Example
• Flocking System Concepts and Example
• Mass Spring System Example
• Conclusion

24
Flocking System
Go Fish!by Xiaoyuan Tu
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Flocking System

• Refines Basic Particle System
• Flocking Forces
• Energy Cutoff

Collision Avoidance
Velocity Matching
Flock Centering
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Flocking System

• BoidltTgt
• Refines BasicParticleltTgt
• Defined in BoidParticle.h
• Data Members
• double energy
• static double Energy
• Methods
• Matrix3x3 RotatetoLocalCoordinates()
• bool InFieldofView(Vector3d X, double radius,
  double viewAngle) const
• bool InFieldofView(BoidltTgt pParticle, double
  radius, double viewAngle) const

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Flocking System

• FlockState
• Refines BasicState
• Defined in BoidParticle.h
• Data Members
• Vector3d Tail, Tail2
• double roll
• flock_update_visitor
• Refines default_update_visitor
• updateElement()
• Updates Tail, Tail2, energy

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Flocking Rules

• Applied at each time step
• Forces
• Vector3d AvoidCollisions(int index, Environment
  env, FlockParticleSystemltBoidgt pSystem)
• Vector3d VelocityMatching(int index,
  FlockParticleSystemltBoidgt pSystem)
• Vector3d FlockCentering(int index,
  FlockParticleSystemltBoidgt pSystem)

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Flocking System

• Advance Function
• Not sure
• Apply integrator
• Update state variables

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Flocking System

• Demo

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Outline

• Basic Simulation Concepts
• Particle System Concepts and Example
• Flocking System Concepts and Example
• Mass Spring System Example
• Conclusion

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Mass Spring System

• Demos

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Outline

• Basic Simulation Concepts
• Particle System Concepts and Example
• Flocking System Concepts and Example
• Mass Spring System Example
• Conclusion

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Conclusion

• Developed concepts for a generic physically based
  modeling library
• Implemented concepts related to particle system
  simulations
• Environment, State, Force, Numerical Integrator,
  Particle, Particle System,
• Demonstrated ease of creating complex simulations
  extended from basic library concepts
• Volcano simulation

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Future Work
Modeling System
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References

• BWK99 David Baraff, Andrew Witkin, and Michael
  Kass. Physically based modeling. SIGGRAPH Course
  Notes, Course 36, Los Angeles, 1999.
• BFA02 Robert Bridson, Ronald Fedkiw, and John
  Anderson. Robust treatment of collisions, contact
  and friction for cloth animation. International
  Conference on Computer Graphics and Interactive
  Techniques, pages 594-603, 2002.
• EMF02 Douglas Enright, Stephen Marshner, and
  Ronald Fedkiw. Animation and Rendering of complex
  water surfaces. International Conference on
  Computer Graphics and Interactive Technjques,
  pages 736-744, 2002.
• FSJ01 Ronald Fedkiw, Jos Stam, and Henrik W.
  Jensen. Visual simulation of smoke. International
  Conference on Computer Graphics and Interactive
  Techniques, pages 15-22, 2001.
• FM96 Nick Foster and Dimitri Metaxas. Realistic
  animation of liquids. Graphical Models and Image
  Processing, 58471-483, 1996.
• GBF03 Eran Duendelman, Robert Bridson, and
  Ronald Fedkiw. Nonconvex rigid bodies with
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  871-878, 2003.
• NFJ02 Duc Q. Nguyen, Ronald Fedkiw, and Henrik
  W. Jensen. Physically based modeling and
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  pages 721-728, 2002.
• OH99 James F. OBrien and Jessica K. Hodgins.
  Graphical modeling and animation of brittle
  fracture. International Conference on Computer
  Graphics, pages 137-146, 1999.

37
References

• R83 William T. Reeves. Particle systems --- A
  technique for modeling a class of fuzzy objects.
  ACM Transactions on Graphics, 2(2)91-108, 1983.
• R87 Craig W. Reynolds. Flocks, herds, and
  schools A distributed behavioral model.
  International Conference on Computer Graphics and
  Interactive Techniques, pages 25-34, 1987.
• S90 Karl Sims. Particle animation and rendering
  using data parallel computation. International
  Conference on Computer Graphics and Interactive
  Techniques, pages 405-412, 1990.
• S99 Jos Stam. Stable fluids. International
  Conference on Computer Graphics and Interactive
  Techniques, pages 121-128, 1999.
• S00 Bjarne Stroustrup. The C Programming
  Language (Special Edition). Addison Wesley,
  Reading, MA, 2000.
• TT94 X. Tu and D. Terzopoluos. Artificial
  fishes physics, locomotion, perception,
  behavior. International Conference on Computer
  Graphics and Interactive Techniques, pages 43-50,
  1994.
• WNDS99 Woo, Neider, Davis, and Shreiner. OpenGL
  Programming Guide Third Edition The Official
  Guide to Learning OpenGL, Version 1.2. Addison
  Wesley, New York, 1999.