Lessons Learned from Building a 3D
System for Novices
Jeff Pierce
Carnegie Mellon University
jpierce@cs.cmu.edu
Outline
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About Alice
Some Lessons Learned
Advanced Functionality
Building An Alice World
Building Virtual Worlds: the class
The Problem
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3D faster than Moore’s Law
3D authoring is too hard
“What If” too expensive
Current 3D APIs
– Non-intuitive behavior
– Implementation leaks through
What Alice Is...
• Allows novices to write scripts that
control interactive 3D graphics
• Novices
– 19 year old (non-engineering) college
undergraduates
• Like 3D LOGO…
…with “threads”
Alice is Not...
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Modeler / CAD Package
Keyframing
Multimedia Authoring
VRML Authoring
What Is Alice For?
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Animated Illustrations
Games
Small Virtual Worlds
Rapid Prototyping
Teaching?
• Question really is: “What is 3D graphics
for?”
Alice 99 & Squeak Alice
• Alice 99
– Developed by Stage 3 Research group,
Randy Pausch director, at UVA and CMU
• Squeak Alice
– Port of Alice to Squeak
– Draws on the lessons learned, but lacks
some functionality
Alice 99 Architecture
Visual Basic Alice Interface
User Scripts
Alice OOP Classes
Animation Engine
Simulation Scheduler
Database/Matrix Services
C / C++
Extension
Libraries
(Ex. UNC
particle
system)
Microsoft Direct 3D (Retained Mode )
Squeak Alice Architecture
Morphic Interface
User Scripts
Wonderland Classes
(Actors, Animations, Cameras,
Scheduler, etc.)
Database/Matrix Services
Balloon 3D (Immediate Mode)
Key Squeak Alice Classes
• Wonderland
– Encapsulates a 3D world
• Scheduler
– Responsible for making time pass
• WonderlandActor
– Encapsulates behaviors for actors
• WonderlandCamera
– Responsible for drawing the world
The Alice Main Loop
DO Forever
Process Any Input Events
FOR Each Scheduled Animation DO
Update Affected Objects
FOR Each Camera DO
Render the Updated World
Demo
Design Philosophy
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Focus on Behavior Specification
Observe the 90/10 Rule
All Tradeoffs in Favor of the Novice
Let the Tutorial Drive the Design
Tutorial Drives the Design
• Two Parts:
– Design
– Teaching
• As designers, we control both halves
• Teaching influences design
Research Approach
• Psychology/Linguistic Literature
– inspires and informs good decisions
– does not dictate
• User Observation
– ferrets out bad decisions
• Need Both
User Observation
• N > 120
• Two Person Talk Aloud Protocol
– eavesdropping
• Critical Incident Reporting
– exit interviews after extended use
Outline
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About Alice
Some Lessons Learned
Advanced Functionality
Building An Alice World
Building Virtual Worlds: the class
First, a disclaimer...
You (and I)
are not our users...
99%
99%
My Our
Users
Users
1%
You Are Here
You (and I)
are not our users...
99%
99%
My Our
Users
Users
1%
You Are Here
...but your students are
XYZ Considered Harmful
Avoid Small Cognitive
Hit on Every Operation
forward
up
left
Vocabulary Matters
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X, Y, Z
Translate
Rotate
Scale
Depth
RGB Triples
• (0, 0, 255)
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Left, Up, Forward
Move
Turn
Resize
FrontToBack
Color names

blue
Controlled Exposure
To Power: Animation
• Extend, Don’t Abandon Knowledge
• Optional Keywords
• Allow combinations when possible
Distance = Speed x Time
• Duration
• Speed
• Style (interpolation function)
Animation Examples
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bunny move: up
bunny move: up distance: 1
bunny move: up distance: 1 duration: 5
bunny move: up distance: 1 speed: 2
bunny move: up speed: 2
bunny move: up speed: 2 for: 5
bunny move: up distance: 1
style: abruptly
All Actors Are
Reference Frames
• Controlled Exposure To Power
• Optional asSeenBy keyword
bunny move: forward distance: 1
bunny move: forward distance: 1
asSeenBy: camera
• Direct 3D 5.0
UP is Fundamental
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Essential like cameras and lights
Not gravity, Just “Up”
Panning cameras
pointAt:
Even without a ground plane, observer
supplies an “Up” vector
Turning at Speed
• bunny turn: left speed: 2
• Units?
Turns/Second
22
RPM
9
Unitless 1-10
7
Fast/Medium/Slow
6
Degrees/Second
3
Seconds/Turn
2
Radians/Second
1
N=50
Turns/Second
22
RPM
9
Unitless 1-10
7
Fast/Medium/Slow
6
Degrees/Second
3
Seconds/Turn
2
Radians/Second
1
N=50
Turn
• There are only two kinds of turning
• bunny turn: left turns: 1
• bunny turn: right turns: 1
• bunny turn: forward turns: 1
• bunny turn: back turns: 1
Roll Is…
• Invisible to 70% of Subjects
• bunny roll: left turns: 1
• bunny roll: right turns: 1
Parts
• First-Class and Part properties
• Distinct from Parent-Child relationship
• Boundaries in the scene graph
More About Parts
• More than Picking
– property setting (color)
– delete
Table
Ball
Legs (parts)
More About Parts
• More than Picking
– property setting (color)
– delete
Table
Ball
Legs (parts)
Pulling Objects Apart
• Is it still a part?
Scale (Resize)
• bunny resize: 0.5
• Scale is a terrible term
• Many Traditional APIs
– Matrix Scale == Scaled Space
• Alice
– Tracks the scale factor, later operations
scaled back. A meter is always a meter.
Numbers Matter
• Importance of 0 and 1
– Users often try 1 when they need a number
– Alice uses 0..1 for all bounded ranges
• Novices do not understand “magic ranges”
(0..255, 0..32767)
• 1/4 = 0.25, not 0
• We changed integer division in Python
• Not a problem in Squeak
Undo
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Make “what if” cost-free
Animates
Users are insensitive to duration
Users are sometimes sensitive to path
Some operations tricky
– start an animation, then UNDO
Problems With Scripting
• Case sensitivity (85%)
• Bunny and bunny the same for novices
• We made Python case insensitive
• This is problematic for Squeak
• Typing (63%)
• Syntax (45%)
– parentheses, dots, commas
Novices Want End-to-End
Teddy 2 by Takeo Igarashi
3D Paint Tool
by Dennis Cosgrove
Outline
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About Alice
Some Lessons Learned
Advanced Functionality
Building An Alice World
Building Virtual Worlds: the class
Some Higher Level Commands
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obj1 pointAt: obj2
obj1 alignWith:obj2
obj1 place: onTopOf object: obj2
obj1 standUp
obj1 destroy: 2
obj1 resizeLikeRubber
dimension: topToBottom
Animations Are Objects
spin
spin
spin
spin
spin
:= bunny turn: left turns: 1
pause
resume
stop
start
spin loop: 2
spin loop
spin stopLooping
Composing Animations
jump := bunny move: up distance: 1.
fall := bunny move: down distance: 1.
hop := w doInOrder: {jump. fall}.
hop start
spinJump := w doTogether:
{hop. bunny turn: left turns: 1}.
spinJump loop
Adding Responses
newReaction :=
bunny respondWith:
[:event | bunny turn: left turns: 1]
to: leftMouseClick
bunny addResponse:
[:event | bunny move: up distance:
2] to: leftMouseClick
bunny removeResponse: newReaction
to: leftMouseClick
Outline
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About Alice
Some Lessons Learned
Advanced Functionality
Building An Alice World
Building Virtual Worlds: the class
The Process
• (1) Create Models
– Objects created in external CAD Packages
– Alice reads common polygonal 3D file formats
• (2) Paint Textures on Models
– Unfolding and (U,V) coordinate mapping
– Good tools somewhat rare on PC
• (3) Scripting
ALICE
Alice World =
Opening Scene
+
Script
whiz = box.turn(left, Rate=20)
box.setReaction(LeftMouseDown, whiz)
(Squeak Alice lacks the Opening Scene mechanism)
Opening Scene
• Insert Objects Via Menus
• Drive Camera(s) into position
• Tweak the scene
– Direct Manipulation
– GUI tools
– command box
• Save
Making and Running Scripts
• Define Behaviors
• Launch Behaviors
• As program runs evaluate new code
– command box
– GUI tools
– Direct Manipulation
• Reset / Undo when necessary
Outline
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About Alice
Some Lessons Learned
Advanced Functionality
Building An Alice World
Building Virtual Worlds: the class
Building Virtual Worlds
• Semester-long course at CMU
• Mix of computer science, art, drama,
design, and architecture students
• Every 2-3 weeks (6 projects total)
– students randomly assigned to new
interdisciplinary group of 4-5 people
– must build a virtual world using Alice
• Open showcase at end of semester
Video
Availability
• Alice 99
– Runs on Windows 95 / 98 / 2000 / NT / XP
– Free
– http://www.alice.org
• Squeak Alice
– Runs on anything Squeak does
– Free
– http://www.squeak.org
The Authors
Matthew Conway, Steve Audia, Tommy Burnette,
Dennis Cosgrove, Kevin Christiansen, Rob Deline,
Jim Durbin, Rich Gossweiler, Shuichi Koga,
Chris Long, Beth Mallory, Steve Miale,
Kristen Monkaitis, James Patten, Jeff Pierce,
Joe Shochet, David Staack, Brian Stearns,
Richard Stoakley, Chris Sturgill, John Viega,
Jeff White, George Williams, Randy Pausch
Lessons Learned from Building a 3D
System for Novices
http://www.alice.org
Jeff Pierce
Carnegie Mellon University
jpierce@cs.cmu.edu