an efficient brush model for physically-based 3d painting
DESCRIPTION
An Efficient Brush Model for Physically-Based 3D Painting. Nelson S.-H. CHU ([email protected]) Chiew-Lan TAI ([email protected]) The Hong Kong University of Science and Technology October 9, 2002, Beijing, China. Input: Brush movements. Simulation of Brush & ink. Output: Realistic brushwork. - PowerPoint PPT PresentationTRANSCRIPT
An Efficient Brush Model for Physically-Based 3D Painting
Nelson S.-H. CHU ([email protected])Chiew-Lan TAI ([email protected])
The Hong Kong University of Science and Technology
October 9, 2002, Beijing, China
Pacific Graphics 2002, Beijing, China
Overview Brush simulation for digital painting
Chinese brush Physically-based Interactive
Input: Brush movements
Simulation of Brush & ink
Output: Realistic brushwork
Pacific Graphics 2002, Beijing, China
Motivation Digital painting
Convenient, easy to experiment 2D mark-making methods
Works well for ‘hard’ media like pastel Spotted shape as brush footprint
Painting & strokes made using commercial software Corel
Painter
2D dab shapes
Pacific Graphics 2002, Beijing, China
Motivation Chinese brush
Expressive lining instrument Soft-yet-resilient quality 惟笔软则奇怪生焉。– 蔡邕 ( 东汉 )
Deft manipulation Spontaneous painting style
Spontaneity Rhythmic vitality
Execution + Elastic Brush
Pacific Graphics 2002, Beijing, China
Motivation
By Zhao Shao’ang
Pacific Graphics 2002, Beijing, China
Motivation
By Wu Guanzhong 1999
Pacific Graphics 2002, Beijing, China
Motivation Extend the expressiveness of Chinese brushes
into digital domain Help promote Chinese cultural heritage
Explore new possibilities for development 保留传统 , 只有发展才能保留 , 不发展就不可能保留。– 吴冠中
Creates new computer graphics tools High-quality calligraphic Oriental fonts Non-photorealistic rendering of 3D objects
Pacific Graphics 2002, Beijing, China
Previous Work Stroke Appearance Brush Model + Painting Process
Pacific Graphics 2002, Beijing, China
Previous Work Stroke Appearance
B. Pham ’91 (B-spline + offset curves) S. Hsu et al. ’94 (Picture deformation)
Brush Model + Painting Process
Pacific Graphics 2002, Beijing, China
Previous Work Stroke Appearance Brush Model + Painting Process
Geometric S. Strassmann ’86 (1D texture) Painting Software Corel Painter (2D dab shape)
Physically-based J. Lee ’99 (Homogeneous elastic rods) S. Saito et al. ’99 (Point mass at tip + Bezier spine) B. Baxter et al. ’01 (Spring-mass system)
Geometric + Physical behaviors H. Wong et al. ’00 (Cone) S. Xu et al. ’02 (Tuft-like objects)
Pacific Graphics 2002, Beijing, China
Our Brush Model
Pacific Graphics 2002, Beijing, China
Our Brush Model
Model in full gear Without tip splitting
Without lateral spreading
No deformation at all(brush penetrates
paper)
Pacific Graphics 2002, Beijing, China
Brush Modeling Layered approach
Brush skeleton Determines dynamics
Brush surface Determines footprint
Surface
Skeleton
Pacific Graphics 2002, Beijing, China
Brush Modeling Brush Skeleton
Spine Connected line segments For general bending
Lateral nodes Slides along the sides of a
spine node For lateral deformation
Pacific Graphics 2002, Beijing, China
Brush Modeling Brush Surface
Cross-section = two half-ellipses Sweep along spine Bristle splitting by alpha map
Tuft cross-sectionpaper footprint
Pacific Graphics 2002, Beijing, China
Brush Dynamics Variational approach
Brush skeleton of next frame obtained by energy minimization
Minimum principle for incremental displacements As a constrained optimization problem
Objective function: Total Energy = deformation energy + frictional energy
Constraints: All nodes above paper Solve using sequential quadratic programming
Pacific Graphics 2002, Beijing, China
Brush Dynamics Skeleton spring system
Angular Springs:between
consecutive spine nodes
Angular Springs:between
consecutive lateral nodes
Displacement Springs:
between spine nodes & its lateral
nodes
Pacific Graphics 2002, Beijing, China
Brush Dynamics Brush behaviors expected by real-brush
users Brush Plasticity
Wetted brush are plastic Paper pore resistance
Small pores on paper surface Fine brush tip gets trapped
Pacific Graphics 2002, Beijing, China
Brush Dynamics Brush Plasticity
Shift the spring energy function so that the zero (lowest) energy position is now at
= min (’, ),’ = position from last
frame = max. shift
Pacific Graphics 2002, Beijing, China
Brush Dynamics Paper pore Resistance
As a moving blocking-plane constraint Prevents brush tip from going towards the
direction it is pointing Adjustable lead distance
Pacific Graphics 2002, Beijing, China
Summary of New Features Brush flattening and spreading Brush splitting at bristle level Brush Plasticity Paper pore resistance
Pacific Graphics 2002, Beijing, China
Summary of New Features Brush flattening and spreading
Lateral nodes Brush splitting at bristle level Brush Plasticity Paper pore resistance
Pacific Graphics 2002, Beijing, China
Summary of New Features Brush flattening and spreading
Lateral nodes Brush splitting at bristle level
Alpha map Brush Plasticity Paper pore resistance
Pacific Graphics 2002, Beijing, China
Summary of New Features Brush flattening and spreading
Lateral nodes Brush splitting at bristle level
Alpha map Brush Plasticity
Zero-shifting Paper pore resistance
Pacific Graphics 2002, Beijing, China
Summary of New Features Brush flattening and spreading
Lateral nodes Brush splitting at bristle level
Alpha map Brush Plasticity
Zero-shifting Paper pore resistance
Blocking-plane constraint
Pacific Graphics 2002, Beijing, China
Video Demonstration
Pacific Graphics 2002, Beijing, China
Conclusions Efficient model for brush deformation
Plausible brush dynamics Bending, flattening, spreading & splitting Plasticity Paper pore resistance
Real-time on consumer-level PC Oil or watercolor brushes can be modeled
with small modifications
Pacific Graphics 2002, Beijing, China
Future Work Painting media modeling
Ink diffusion Paper texture Tuft hierarchy
Physics simulation Investigate vectorial dynamics
User interface Haptic input device Stereo display
Pacific Graphics 2002, Beijing, China
Thank you!
Questions?
Slide show of sample output
Contact: [email protected] [email protected]
Pacific Graphics 2002, Beijing, China
Brush Dynamics
Vectorial approach F=ma, for a certain F, small m large a Need to solve stiff differential equations
Variational approach Get into next state by minimization energy
functional Minimum principle for incremental displacements
Observations Little inertia, highly damped forces Almost always in steady state
Pacific Graphics 2002, Beijing, China
Brush Dynamics
Spine BendingEnergy
Lateral DeformationEnergy
Internal Energy
+
+Total Energy
DeformationEnergy
FrictionalEnergy
+=