Pen Based User Interface Issues

1
Pen Based User Interface Issues

• CSE 490RA
• January 25, 2005

2
Lecture outline

• Physical input devices
• Limited range of devices / continuous vs.
  discrete
• Theory Fitts law
• Basic stylus issues
• Large number of mechanical challenges
• Application Design considerations
• Mode switch issues
• Modes are evil
• Aspects of pen computing
• Abstract writing, gestures, control

3
Physical Input Devices

• Discrete

• Analog

4
HCI Theory

• Understand human tradeoffs in motion
• Fitts law
• Steering law

5
Experiment measure time to move cursor to target
W
T(A, W) Targeting time for amplitude A and width
W
A
Cursor
Target
6
Index of difficulty

• How does T behave as a function of A (W fixed)?
• How does T behave as a function of W (A fixed)?

7
Fitts law

• A tasks movement difficulty is given by ID
  log2(A / W)
• ID index of difficulty
• A amplitude of the move
• W width of the target region
• T a b ID

8
Interpretation of Fitts Law

• Scale invariance
• Dependence on A/W
• Exponential targeting
• Log factor as in binary search

9
Menu design

• What can you say about the cost of accessing
  items in the following menu
• Cursor is at the top of the menu

10
Design a menu where each entry has equal access
time
11
Basic Stylus Issues

• List three challenges in using a stylus on the
  Tablet PC

12
Basic stylus issues

• What techniques can be used at the application
  level to overcome these problems?

13
Uses of the stylus

• Direct writing
• Abstract writing
• Pointing
• Selecting
• Gesture
• Direct manipulation
• Control

14
Mode Problem

• Cognitive difficulties in remembering / keeping
  track of modes
• Which mode?
• Remapping operations
• Retaining mode across context switch
• But modes are very useful
• Efficient use of limited input controls
• Not all modes are the same
• Shift key vs. Caps Lock
• Mouse move vs. mouse drag
• Pen color

15
Does the automobile interface (for the driver)
have modes?
16
Mode issues in pen computing

• Adding modes to the pen
• Barrel button
• Secondary button with non-dominant hand
• Eraser tip
• Pressure
• Explicit mode buttons
• Area based modes (writing area, gesture area,
  control area, etc.)
• Cursor feedback
• Importance of visual cues for informing user
• Errors in crossing mode boundaries

17
Abstract writing

• Enter text with specialized, stroke based
  recognition
• Optimized for automatic recognition
• Not human readable
• Character based or word based

18
Examples
Cirrus (Georgia Tech)
Graffiti (Palm)
19
Quikwrite Perlin, NYU
20
Quikwrite Perlin, NYU
21
Control

• Widgets design for stylus use

22
Flow Menu

• Use movement through octants for control
  information

Move
Item
100
100
Text
Item
Zoom
Highlight
200
66.6
200
66.6
Shape
400
50
400
50
75.0
100.0
800
25
800
25
Custom
Custom
23
Interaction with direct manipulation
Move
Item
Zoom
Highlight
24
CrossY Crossing based UI

• Specify operations by drawing through

25
Gestures

• Commands issued with a single stroke
• May be drawn or invisible
• Support from SDK
• Register gestures to be recognized
• UI Issues
• Similar to keyboard short cuts
• Speed up for experts
• Hard to learn / remember

26
Gestures

• Ambiguity
• Distinction between gestures
• Distinction between gesture and other ink
• Robustness
• Handling misrecognized gestures
• False positive
• False negative
• Gesture initiated actions should be undoable