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Transcript of Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature...
![Page 1: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/1.jpg)
Hair Simulation
COMP 768 Qi Mo
![Page 2: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/2.jpg)
Motivation
• Cosmetic prototyping
• Entertainment industry
- Feature animation
- Interactive systems
![Page 3: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/3.jpg)
Motivation
• Cosmetic prototyping
• Entertainment industry
- Feature animation
- Interactive systems
![Page 4: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/4.jpg)
Motivation
• Cosmetic prototyping
• Entertainment industry
- Feature animation
- Interactive systems
![Page 5: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/5.jpg)
Motivation
• Cosmetic prototyping
• Entertainment industry
- Feature animation
- Interactive systems
![Page 6: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/6.jpg)
Motivation
• Cosmetic prototyping
• Entertainment industry
- Feature animation
- Interactive systems
![Page 7: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/7.jpg)
Motivation
• Cosmetic prototyping
• Entertainment industry
- Feature animation
- Interactive systems
![Page 8: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/8.jpg)
Motivation
• Cosmetic prototyping
• Entertainment industry
- Feature animation
- Interactive systems
![Page 9: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/9.jpg)
Challenges
• Over 100,000 hair strands
• Real hair properties still under research
![Page 10: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/10.jpg)
Overview
• Styling Geometry of hair
Density, distribution, orientation of hair strands
• Simulation Dynamic motion of hair
Collision between hair and other objects Mutual hair interactions
• Rendering Light scattering and shadows
![Page 11: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/11.jpg)
Overview
• Styling Geometry of hair
Density, distribution, orientation of hair strands
• Simulation Dynamic motion of hair
Collision between hair and other objects Mutual hair interactions
• Rendering Light scattering and shadows
![Page 12: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/12.jpg)
Hair Geometry
• Curliness: Straight, wavy, curly, etc.
• Shape of cross-section - Asian hair strand: circular
- African hair strand: very elliptical
- Caucasian hair strand: between the two
![Page 13: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/13.jpg)
Hair styling
• Attaching hair to the scalp
• Global hair shape
• Fine details
![Page 14: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/14.jpg)
Attaching hair to the scalp
• 2D Placement
• 3D Placement
• Distribution of hair strands on the scalp
![Page 15: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/15.jpg)
Global Hair Shape Generation
• Geometry-based hairstyling - Parametric surface
- Wisps and generalized cylinders
• Physically-based hairstyling - Fluid flow
- Styling vector and motion fields
• Generation of hairstyles from images
![Page 16: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/16.jpg)
Global Hair Shape Generation
• Geometry-based hairstyling - Parametric surface
- Wisps and generalized cylinders
![Page 17: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/17.jpg)
Global Hair Shape Generation
• Geometry-based hairstyling - Parametric surface
- Wisps and generalized cylinders
![Page 18: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/18.jpg)
Global Hair Shape Generation
• Geometry-based hairstyling - Parametric surface
- Wisps and generalized cylinders
![Page 19: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/19.jpg)
Global Hair Shape Generation
• Physically-based hairstyling - Fluid flow
- Styling vector and motion fields
![Page 20: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/20.jpg)
Global Hair Shape Generation
• Physically-based hairstyling - Fluid flow
- Styling vector and motion fields
![Page 21: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/21.jpg)
Global Hair Shape Generation
• Physically-based hairstyling - Fluid flow
- Styling vector and motion fields
![Page 22: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/22.jpg)
Global Hair Shape Generation
• Geometry-based hairstyling - Parametric surface
- Wisps and generalized cylinders
• Physically-based hairstyling - Fluid flow
- Styling vector and motion fields
• Generation of hairstyles from images
![Page 23: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/23.jpg)
Finer Details
![Page 24: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/24.jpg)
Finer Details
![Page 25: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/25.jpg)
Finer Details
![Page 26: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/26.jpg)
Hair Mechanics• Difficult to shear and stretch
• Easy to bend and twist
• Anisotropic friction
• Hair geometry also affects motion
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Dynamics of Individual Strand
• Mass-spring systems
• One dimensional projective equations
• Rigid multi-body serial chain
• Dynamic super-helices
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Mass-Spring Systems
• Particles connected by stiff springs bending rigidity ensured by angular spring at each joint
Simple and easy to implement
But does not account for tortional rigidity or non-stretching of each strand
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One-dimensional Projective Equations
• Hair strand as a chain of rigid sticks
Easy to implementEfficientNon-stretchingBending
No tortional stiffnessDifficult to handle
external punctual forces
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Rigid Multi-body Serial Chain
• Hair strand as a rigid multi-body open chain
• Bending and twisting DOFs only, stretching DOF removed• Motion computed using forward dynamics
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Super-Helices
• Accurate Mechanical Model
Kirchhoff Equation and Cosserat Curves
![Page 32: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/32.jpg)
Super-Helices Model for Strands
• Cosserat curve: a one-dimensional rod
• A material frame defined at each point on the centerline
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Kinematics
r (s, t) – centerline
s – curvilinear abscissa along r
t – time ni(s, t) – axis of material frame
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Kinematics
Ω(s, t) – Darboux Vector
τ(s, t) – twist
κi (s, t) - curvatures
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Spatial Discretization
N – number of segments
Q – index of segments 1≤Q ≤ N
qi,Q(t) – constant curvatures & twist
χQ (s) – characteristic function of Q
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Dynamic Equations• Solve equations of motion using
Lagrangian mechanicsq (t) – generalized coordinates
T (q, , t) – kinetic energy
U (q, t) – internal energy
D (q, , t) – dissipation potential
F (s, t) – linenic density of forces
JiQ (s, q, t) – Jacobian matrix
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Energy Terms
ρS – mass per unit length
(EI)0 – torsional stiffness
(EI)1,2 – bending stiffness
κ0 – natural twist
κ1,2 – natural curvatures
γ – internal friction coefficient
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Equation of Motion• Symbolic Integrations
– inertia matrix
– stiffness matrix
qn – rest position
A – all remaining terms
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Key Features
• Discrete model for Kirchhoff equations
• Space integrations performed symbolically
• Stiff constraint of inextensibility incorporated into reconstruction process, therefore removed from the equations of motion
• Stable simulation even for small N
• When N →∞, Kirchhoff Eq recovered
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Parameters of Model
• Chosen based on physical measurements
- Hair mass
- Mean radius and ellipticity
- Natural curliness:
- Internal friction γ
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Results and Validation
![Page 42: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/42.jpg)
Dynamics of a Full Hairstyle
• Hair as a Continuous Medium
• Hair as Disjoint Groups
• Collision detection and response
• Hair-hair and hair-object interaction
![Page 43: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/43.jpg)
Hair as a Continuous Medium
• Fluid Dynamics
• Loosely Connected Particles
• Interpolation between Guide Hair Strands
• Free Form Deformation
![Page 44: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/44.jpg)
Animating Hair with Fluid Dynamics
• Kinematically link each hair strand to fluid particles in their vicinity
• Hair-hair interactions modeled by pressure and viscosity forces between strands
• Hair-body interactions modeled by creating boundary particles around solid objects
Captures the complex interactions of hair strandsCannot capture the dynamic clustering effectsComputationally expensive
![Page 45: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/45.jpg)
Loosely Connected Particles• Use a set of fluid particles that interact in an adaptive
way• Neighboring particles with similar orientations are linked• During motion particles interact with other particles in its
local neighborhood through breakable links• Allows separation and grouping while maintaining
constant hair length
![Page 46: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/46.jpg)
Interpolation between Guide Hair Strands
• Only simulate a sparse set of hair strands• Remaining strands created by interpolation• Only use the guide strands to detect and handle
collisions - Might miss collisions
![Page 47: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/47.jpg)
Free Form Deformation (FFD)
• Define a mechanical model for a lattice surrounding the head
• Lattice deformed using a global volumetric FFD scheme
• Good for simulating complex hairstyles when head motion has low magnitude
• Cannot reproduce discontinuities in hair
![Page 48: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/48.jpg)
Hair as Disjoint Groups
• Group nearby hair strands, simulate groups as independent, interacting entities
Account for discontinuities during fast motionSave computation time
• Simulation of
- Hair strips
- Wisps
![Page 49: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/49.jpg)
Simulation of Hair Strips• Model groups of strands using a thin flat patch,
e.g. a NURBS surface
Achieves real time using a strip to represent tens or hundreds of hairsLimited in the types of hairstyle and motion
![Page 50: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/50.jpg)
Simulation of Wisps
• Group neighboring strands into wisps
• Wisp representations - Trigonal prism-based wisp
- Typical strand and
random displacements
- Layered wisp model
![Page 51: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/51.jpg)
Multi-resolution Methods
• Tradeoff: performance and realism
• Level-of-detail representations
• Adaptive clustering
![Page 52: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/52.jpg)
Level-of-Detail Representations
• Three discrete levels of detail - strands, clusters, and strips• Common representation by subdivided curves and
surfaces• Collision detection using Swept Sphere Volumes• Dynamic level transition based on visibility, viewing
distance, and motion
![Page 53: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/53.jpg)
Adaptive Clustering
• Continuously adjustment with Adaptive Wisp Tree (AWT)
• Dynamically splits or groups wisps while preserving tree-like structure
• Implicitly models hair interactions
![Page 54: Hair Simulation COMP 768 Qi Mo. Motivation Cosmetic prototyping Entertainment industry - Feature animation - Interactive systems.](https://reader035.fdocuments.in/reader035/viewer/2022062314/56649cec5503460f949b8bd2/html5/thumbnails/54.jpg)
Hair Rendering
• Representation
• Light scattering in hair
• Hair self-shadowing
• Acceleration
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Representation
• Explicit representation
curved cylinder, trigonal prism, triangle strips
thin -> undersampling -> blending techniques
• Implicit representation
volumetric textures, cluster model with density
avoid aliasing, but traversal may be expensive
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Hair Optical Properties
• Hair composed of amorphous proteins as a transparent medium with an index of refraction η= 1.55
• Contain pigments that absorb light in a wavelength-dependent way -> color
• Circular/elliptical fibers treated as one-dimensional
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Light scattering
• One-dimensional reformulation of BRDF
• Reflection and refraction in cylinders
• Physical measurement of scattering
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Light Scattering Model
• Kay and Kajiya’s model
• Marschner’s model
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Self-shadowing
• Challenges - complex geometry - strong forward scattering properties
• Ray-casting through a volumetric representation• Shadow maps
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Rendering Acceleration
• Approximating Hair Geometry
• Interactive Volumetric Rendering
• Graphics Hardware
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Summary• Styling Hair geometry
Attaching hair to scalp, generate global shape, capture finer details• Simulation Hair mechanics
Mass-spring systems, One dimensional projective equations, Rigid multi-body serial chain, Dynamic super-helices
Continuous medium, disjoint groups
Multi-resolution methods• Rendering Hair optics
Representation, light scattering, self-shadowing, acceleration techniques
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Open Challenges
• Physically-based realism
• Visual realism with high user control
• Computations acceleration
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Reference
1. Anjyo, Usami & Kurihara (1992): A simple method for extracting the natural beauty of hair
2. Bertails, Kim, Cani & Neumann (2003): Adaptive wisp tree – a multiresolution control structure for simulating dynamic clustering in hair motion
3. Chang, Jin & Yu (2002): A practical model for hair mutual interactions
4. Hadap & Magnenat-Thalmann (2001): Modeling dynamic hair as a continuum
5. Koh & Huang (2000): Real-time animation of human hair modeled in strips
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6. Kurihara, Anjyo & Thalmann (1993): Hair animation with collision detection
7. L'Oréal (2005): Hair Science www.hair-science.com8. Magnenat-Thalmann & Hadap (2000): State of the art in
hair simulation9. Petrovic, Henne & Anderson (2007): Volumetric methods
for simulation and rendering of hair10. Plante, Cani & Poulin (2001): A layered wisp model for
simulating interactions inside long hair11. Rosenblum, Carlson & Tripp (1991): Simulating the
structure and dynamics of human hair: Modeling, rendering, and animation
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12. Volino & Magnenat-Thalmann (1999): Animating complex hairstyles in real-time
13. Watanbe & Suenaga (1992): A trigonal prism-based method for hair image generation
14. Ward, Bertails, Kim, Marschner, Cani & Lin (2007): A survey on hair modeling: styling, simulation and rendering
15. Ward & Lin (2003): Adaptive grouping and subdivision for simulating hair dynamics
16. Ward, Lin, Lee, Fisher & Macri (2003): Modeling hair using level-of-detail representations