A Gestural Interface to Free-Form Deformation

Transcription

1 A Gestural Interface to Free-Form Deformation Geoffrey M. Draper Parris K. Egbert Department of Computer Science Brigham Young University

2 Introduction Free-Form Deformation (FFD) is a powerful technique for 3D geometric modeling But it is difficult to use! New gestural user interface to FFD Simple to learn and use

3 Overview of Presentation Gesture-based User Interfaces Free-Form Deformation Our System: Freddy How-to-use Algorithmic Review Conclusions

4 Gestural Interfaces (Also known as Pen-based or Sketching Interfaces) Different from a typical GUI User interaction accomplished via ink strokes An attempt to mimic the way people do things in the real world

5 History of Gestural Interfaces Coleman 1969 (text editing using proofreader s symbols) Slow progress in 1970's 's Increasing popularity since 1990's Faster hardware Rubine s automated gesture recognition (1991)

6 Examples of Gestural Interfaces Drag & Drop PalmOS Tivoli: Electronic Whiteboard (Moran et al. 1995, 1997, 1998) Teddy (Igarashi 1999) Di Fiore and Van Reeth (2002)

7 Teddy Gestural interface for simple 3D modeling Inspiration for our work

8 Free-Form Deformation Basic Idea: Surround a geometric model by a 3D lattice of control vertices Every vertex in the model has a specific location relative to the lattice Displace control vertices in lattice Adjust vertices of model to reconcile their previous relative locations with the new position of lattice

9 Free-Form Deformation Illustrated Geometric model surrounded by lattice Deformed lattice produces a deformed model

10 Free-Form Deformation A Question of Interface Today s hardware can calculate FFDs in near real-time yet using FFD can still be a timeintensive, cumbersome process User interfaces for FFD typically require manual positioning and deformation of control lattice Limiting factor is the human/computer interaction

11 Our Solution A Marriage Between FFD and Gestural Interfaces Apply a Gestural interface to FFD Simple ink strokes replace the manual displacement of the FFD lattice FFD + Teddy = Freddy Bend, Twist, Stretch, Squash 3D objects easily, without dealing with individual vertices

12 Freddy Overview Bend Twist Stretch/Squash Now let s discuss each one in turn...

13 Bend High-Level Overview Stroke must begin inside the object, and go outside the object, without going inside again Draw a stroke in the direction you want the object to bend Object will bend along the contours of the stroke

14 Bend What REALLY Happens 3D model is surrounded by FFD lattice Successive planes of lattice are rotated and translated along the slope of stroke to impart a gradual bend to the object

15 Bend Stroke Interpolation/Resampling Must divide stroke into curve segments of equal length; determine rotation angle and translation distance from these

16 Twist High-Level Overview Stroke must begin inside object, pass outside, then go back inside Physical analogy

17 Twist The Rest of the Story Model is surrounded by lattice Planes of lattice are rotated around the object at successively greater degrees, imparting a twisted look to the object

18 Twist Details Rotate lattice between endpoints of the stroke Degree of twist is determined by angle between endpoints

19 Twist Determining the degree of rotation

20 Stretch & Squash Draw a stroke entirely outside the object Click and drag the stroke farther from the object to stretch; or closer to the object to squash Similar to pushing or pulling on a physical object

21 Stretch & Squash Two Flavors Straight strokes Deform object globally Curved strokes Deform object locally

22 Stretch & Squash Straight Stroke Algorithm Calculate the distance between every point in stroke and every vertex in lattice ( ) Calculate the longest distance between stroke and every vertex in lattice ( ) Calculate rise and run between old and new positions of stroke (d x,y ) Offset each lattice-vertex by d x,y * ( - ) /

23 Stretch & Squash Curved Stroke Algorithm Zone of influence : Parallelogram formed between projected enpoints of stroke and the edge of the screen Only displaces vertices of lattice that lie within zone of influence

24 Freddy supports manual selection of specific sub-regions Creates miniature lattice around the selected region Only the selected region is deformed Selection Truly Localized Deformation

25 Future Work What comes next? True volume preservation Animation Lattices of arbitrary topology

26 Concluding Remarks Simpler way of peforming FFD Simplicity versus Precision Intuitive and fast for beginners; quick brainstorming tool for experienced designers At any rate, it s fun...

27 THE END A Gestural Interface to Free-Form Deformation Brigham Young University