DAB:Interactive Haptic Painting with 3D Virtual Brushes Bill Baxter Vincent Scheib Ming C. Lin Dinesh Manocha SIGGRAPH 2001 Presentation by Pin Ren Feb 27 th, 2003

Previous work Computer-Generated Painting Meier 96, Curtis et al. 97, Hertzmann 98, Litwinowicz 97 Modeling of Paint Curtis et al. 97, Cockshott et al. 92, Hasse & Meyer ’92, Kubelka & Munk ’31 Modeling of Brushes & Strokes S. Saito et al. 99, Wong et al. 00, Strassmann 86 User Interface A. R. Smith 78, Painter, Z-Brush, Deep Paint Hanrahan & Haeberli 90, Agrawala et al. 95 Johnson et al. 99, Gregory et al. 00

When computers try to make paintings Can computers really create paitnings artistically? What do the artists think about that? Are they afraid of losing jobs? Are they angry?

“I am not satisfied by those painting machines!” ---- Picasso(really?) Artists are simply not satisfied They don’t like being asked to set some parameters and waiting around for the final pictures. They want to computers to assist their creative work, not to be deprived the fun of making art. They want natural environment,equivalent tools and creation experiences to the real world

“Art is not only about beautiful pictures” Craft of the painting vs. the Art Craft is about the study of materials, and the whole process of painting. Artists cannot divorce one from the other

Motivation 3D deformable brush [action] Haptic feedback [touch] Paint model [sight] User interface [action] [feeling] Capturing the Sight, Touch, Action and Feeling of Painting

dAb System: interface

System Design [flash]

dAb System: Components Brush Model Haptic Model Paint Model

Brush Model Design considerations Interactivity (~30Hz) Unconditional stability Flexibility

Brush Model Dynamic model Spring-mass particle system Geometric model Subdivision surface

Brush Equations Newtonian Dynamics F=ma, or Semi-Implicit numerical integration (Desbrun’s 99) Linear force Non-linear force Constant!

Brush Equations Overdamped inertial system Eliminate explicit damping Solve F=mv (Aristotelian)

Haptics Simple model Designed to run easily at 1kHz Decoupled from dynamics Effective for control

Haptics: Simulation Linear spring Linear spring Nonlinear spring + angular falloff Nonlinear spring + angular falloff Force vector at a point Force vector at a point

Haptics – Linear slope k 2 Normal Force Brush head penetration depth % slope k device limit Normal Force Friction

Bend Buckle Mash Haptics – Non-linear (Spline) Normal Force Brush head penetration depth % 0100 f 1,k 1 f 2, k 2 f 3, k 3

Buckle Haptics – Angular Dependence 45° 0°0°

Painting Model Interactive Oil/Acrylic Paint Make use of 3D Brush

Paint Transfer

Paint Effects Bi-directional paint transfer Glazing wet paint over dry Controlled by various bush pressure and speed Variable wetness Depended on the timing

Paint Layers Surface Reservoir Wet Dry

Paint Blending

Paint Rendering Alpha blend wet over dry Volume of paint determine the opacity Embossing of paint volume Brush is rendered with just the surface layer over a bristle texture

Example Pic (1) James Ball

Example Pic (2) Rebecca Holmberg

Example Pic (3) Rebecca Holmberg

Summary (1) Novel modeling for real world art craft Deformable 3D brush Haptic feedback Paint model

Summary (2) Simple, yet rich interface Strokes Color mixing Brush loading Digital advantages

Future Challenges Improve current models Expand from 2D canvas to 3D models Training and Study

All pics, flashs and video clips from original siggraph presentation slides and their project website:

Thanks! Any Questions?