Particle Systems

• How do we model ``fuzzy'' objects? Objects with
  • ``soft'' boundary
  • changing boundary
  • chaotic behavior

  Examples: Clouds, fire, water, grass, fur

• Could texture map ``fuzziness,'' but changing shape is hard
• Another way is with Particle Systems

  Basic idea: model fuzzy objects as large colletion of particles

  Used to model ``Genesis'' effect in The Wrath of Kahn

Particle Systems

: 

• Animate fuzzy or gaseous objects as a changing cloud of ``particles''
• Aim for overall effects by having many, simple particles
• Each particle has properties:
  • Geometry (point, sphere, line segment)
  • Position
  • Velocity vector
  • Size
  • Colour
  • Transparency
  • State
  • Lifetime

Animating Particles Systems

: 

• New particles are born, old ones die
• State information describes type of particle
• At each time step, based on state
  • Update attributes of all particles
  • Delete old particles
  • Create new particles
  • Display current state of all particles
• To anti-alias, draw line segment from old position to new position
• To draw grass or fur, draw entire trajectory of particle

Particle System Details

: 

• Easy to implement state machine
• Hard part is determining how to make particles act
• Particles usually independent

  Don't know about one another

• Often will model gravity when updating particles
• Render fire etc using transparency

  Brighter where particle system denser