Simulation and Rendering of Liquid Foams Hendrik Kück (UBC, Vancouver) Christian Vogelgsang (FAU...
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Transcript of Simulation and Rendering of Liquid Foams Hendrik Kück (UBC, Vancouver) Christian Vogelgsang (FAU...
Simulation and Rendering of Liquid FoamsHendrik Kück (UBC, Vancouver)Christian Vogelgsang (FAU Erlangen, Germany) Günther Greiner (FAU Erlangen, Germany)
Graphics Interface 2002
MotivationMotivation
• Liquid foams can be found in many places in the real world
• Very difficult / impossible to recreate using standard techniques• extremely complex microscopic
structures • unique optical properties• complex dynamic behaviour
• Liquid foams can be found in many places in the real world
• Very difficult / impossible to recreate using standard techniques• extremely complex microscopic
structures • unique optical properties• complex dynamic behaviour
GoalsGoals
• Visually convincing simulation and rendering of liquid foams• Not: Physically accurate• But: Efficient
• Interaction with external objects• Integration into existing raytracing
systems
• Visually convincing simulation and rendering of liquid foams• Not: Physically accurate• But: Efficient
• Interaction with external objects• Integration into existing raytracing
systems
OutlineOutline
• Structure and dynamics of liquid foams
• Previous work• Simulation of foam dynamics• Shading• Results• Future Work
• Structure and dynamics of liquid foams
• Previous work• Simulation of foam dynamics• Shading• Results• Future Work
Structure of liquid foamsStructure of liquid foams
Plateauborders
LiquidFilms
Plateau bordercross section
Dynamics of liquid foamsDynamics of liquid foams
• Viscoelastic, can behave like• Solids (elastic deformation)• Fluids (viscous flow)
• Film rupture• Rising bubbles
• Viscoelastic, can behave like• Solids (elastic deformation)• Fluids (viscous flow)
• Film rupture• Rising bubbles
• Physics• Durian, 1995
2D foam dynamics
• Physics• Durian, 1995
2D foam dynamics
Previous workPrevious work
• Computer Graphics• Almgren & Sullivan, 1993
Surface Evolver, Interference Colours
• Icart & Arquès, 1999‚2D‘ foam, Interference colours
• Glassner, 2000Soap bubbles, Interference colours
• Durikovic, 2000Soap bubble dynamics,Mass-spring-damper system
• Computer Graphics• Almgren & Sullivan, 1993
Surface Evolver, Interference Colours
• Icart & Arquès, 1999‚2D‘ foam, Interference colours
• Glassner, 2000Soap bubbles, Interference colours
• Durikovic, 2000Soap bubble dynamics,Mass-spring-damper system
General approachGeneral approach
• Use simple model in simulation step
• Fixed size spheres• No explicit computation
of foam micro geometry• Forces acting on spheres• Output sphere geometry
• In ray-tracing step• Reconstruct liquid films
and Plateau borders• Use appropriate shading
models
• Use simple model in simulation step
• Fixed size spheres• No explicit computation
of foam micro geometry• Forces acting on spheres• Output sphere geometry
• In ray-tracing step• Reconstruct liquid films
and Plateau borders• Use appropriate shading
models
Bubble Bubble ForcesBubble Bubble Forces
• Soap films minimize surface area due to surface tension
• Soap films minimize surface area due to surface tension
Bubble Bubble ForcesBubble Bubble Forces
• Soap films minimize surface area due to surface tension
• Soap films minimize surface area due to surface tension
Bubble Bubble ForcesBubble Bubble Forces
• Soap films minimize surface area due to surface tension
• Soap films minimize surface area due to surface tension
Bubble Bubble ForcesBubble Bubble Forces
• Soap films minimize surface area due to surface tension
• Soap films minimize surface area due to surface tension
120°
Bubble Bubble ForcesBubble Bubble Forces
• Model with 2 spring forces per pair of overlapping spheres• Attractive force• Repulsive force
• Model with 2 spring forces per pair of overlapping spheres• Attractive force• Repulsive force
SimulationSimulation
• Forces acting on spheres due to • Contact with other spheres/bubbles• Viscosity • Air resistance• Gravity• Contact with external objects
• Assumption: Bubbles have no mass Forces have to add up to 0 for each bubble• Results in 1. order ODE system
• Forces acting on spheres due to • Contact with other spheres/bubbles• Viscosity • Air resistance• Gravity• Contact with external objects
• Assumption: Bubbles have no mass Forces have to add up to 0 for each bubble• Results in 1. order ODE system
SimulationSimulation
• Start with randomly generated bubbles • Initial simulation to get a stable
configuration• For each animation frame
• Randomly add/remove spheres• Numerical integration to compute sphere
positions for that point in time• Generate sphere geometry
• Flatten spheres at external objects
• Start with randomly generated bubbles • Initial simulation to get a stable
configuration• For each animation frame
• Randomly add/remove spheres• Numerical integration to compute sphere
positions for that point in time• Generate sphere geometry
• Flatten spheres at external objects
RenderingRendering
• Special shader
• Invoked at every ray/sphere intersection• Has to
• Decide if intersection corresponds to Plateau border or liquid film
• Perform shading using corresponding shading model
• Special shader
• Invoked at every ray/sphere intersection• Has to
• Decide if intersection corresponds to Plateau border or liquid film
• Perform shading using corresponding shading model
Shading model selectionShading model selection
• Base decision on the order in which the ray enters and leaves spheres
• Shading only for some intersections
• Approximate separating films by averaging of adjacent intersections
• Base decision on the order in which the ray enters and leaves spheres
• Shading only for some intersections
• Approximate separating films by averaging of adjacent intersections
Bubble 1Bubble 2
• 2 different cases• Overlap of 3 spheres• Empty space between spheres
• 2 different cases• Overlap of 3 spheres• Empty space between spheres
Plateau BordersPlateau Borders
Liquid Film Shading Liquid Film Shading
• Fresnel reflection• (Interference
Effects)
• Fresnel reflection• (Interference
Effects)
Plateau Border ShadingPlateau Border Shading
• High curvature• Refraction & total
reflection randomize light direction
• Our shading model• Simple light diffusion
approximation (multiple scattering)
• Single scattering
• High curvature• Refraction & total
reflection randomize light direction
• Our shading model• Simple light diffusion
approximation (multiple scattering)
• Single scattering
ResultsResults
• Implemented for Mental Ray® as combination of geometry shader and material shader
• Implemented for Mental Ray® as combination of geometry shader and material shader
Resolution: 800x630 ~700 bubbles
~4 s. simulation 40 s. rendering
Future workFuture work
• Improve shading models• Interference effects• Simulation of multiple scattering
• Level of detail approach• Efficient simulation and rendering of
arbitrary dense foams at arbitrary scale
• Improve shading models• Interference effects• Simulation of multiple scattering
• Level of detail approach• Efficient simulation and rendering of
arbitrary dense foams at arbitrary scale
QuestionsQuestions
AcknowledgementsThis project was supported by Animation/VFX (SZM Studios, Munich, Germany)
Special thanks to Horst Hadler and Michael Kellner
AcknowledgementsThis project was supported by Animation/VFX (SZM Studios, Munich, Germany)
Special thanks to Horst Hadler and Michael Kellner