Rapid and Expressive Prototyping on Cell Phones via Script Embedding

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Rapid and Expressive Prototyping on Cell Phones
via Script Embedding

• Jingtao Wang
• Computer Science Division
• jingtaow_at_cs.berkeley.edu

2
Agenda

• Motivation
• Challenges in creating cell phone app
• Overview of popular mobile development platforms
• Low threshold and high ceiling, the script
  embedding approach
• Summary

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The Popularization of Cell Phones
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Cell Phone is THE Portable Computing Device

• Global penetration reached 50 (3.3 Billion) on
  11/29/2007
• 59 countries had cell phone market share over
  100
• Luxembourg 158
• Hong Kong 140
• Italy 122
• United States 81
• China 42
• India 23 (largest growth market)
• There are only around 850 million PCs in the
  world.

Data from Informa Telecoms Media
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Opportunities and Challenges of Cell Phones

• The bright side
• Portable, always with you
• Always on, always connected to the internet
• Seamless integration with ones social networks
• High market penetration throughout the world
• The dark side
• Limited resources (CPU, memory, screen, input
  modality)
• Highly diversified hardware and software
  implementations
• Incomplete development tools and libraries
• Proprietary hardware/software decrease
  competition and add costs in development and
  distribution

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Threshold and Ceiling
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An Overview of Mobile Development Platforms - 1

• Mainstream (non-smart) Phones (more than 90
  market share)
• J2ME (Java 2 Micro Edition)
• BREW (Binary Runtime Environment for Wireless)
• Flash Lite
• HTML, WAP/WML

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An Overview of Mobile Development Platforms - 2

• Smart Phones (less than 10 market share)
• Windows Mobile (Embedded Visual C, .Net
  Framework Compact Edition)
• Linux (C/C, Java, J2ME)
• Symbian (C, Python)
• Palm (C/C, J2ME)
• Flash Lite
• BREW
• HTML/AJAX, WAP/WML

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J2ME

• Best availability on different platforms
• Can leverage knowledge and resources from desktop
  Java
• Good debugging support
• Poor UI framework/libraries
• Inconsistent behaviors in different devices
  (write once, debug everywhere)
• Poor performance (no JIT on most devices)
• Low ceiling (can only do what the built-in
  libraries allow one to do)
• Signature required to access certain functions

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BREW

• Using C/C as the host language
• Excellent performance (applications run as
  compiled native code)
• Small target application size and little overhead
• High ceiling (can access all the capabilities of
  the phone)
• The only widely available native API for
  non-smart phones
• Steep learning curve
• Bad UI library
• More costs for the development environments and
  the development process
• Hard to debug (different behaviors between the
  simulator and the real device)
• Troublesome coding restrictions
• Signature required to run any applications on a
  cell phone

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Flash Lite

• Flash Lite 2.x similar to Flash 7.0
• Excellent IDE/Emulator support
• Powerful functions for animation/vector graphics
• Low learning threshold
• Low runtime performance
• Hard to access functions not provided, low
  ceiling
• ActionScript Stuck

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HTML, WAP/WML

• Available on almost all cell phones
• Low learning threshold
• Easy to debug (functions implemented on the
  server side)
• Low ceiling
• Limited interactivity function support
• Almost impossible to access local resources of
  the cell phone
• High latency, requires network connection

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Windows Mobile Embedded Visual C

• Excellent performance
• Intermediate learning curve for existing C/C
  programmers
• Relatively steep learning curve for non-C/C
  programmers
• Easy to access hardware features
• Excellent UI framework and UI builder
• Excellent IDE/debugger support
• Excellent emulator support
• Limited device penetration

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Windows Mobile .Net Framework Compact Edition

• Medium to Good performance
• Low learning threshold
• Excellent UI framework and UI builder
• Excellent IDE/debugger support
• Excellent emulator support
• Extra space overhead (2 mb)
• Limited device penetration

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Symbian C

• Excellent performance
• High learning threshold
• Reasonable UI framework
• High ceiling
• High market share among smart phones
• Poor IDE/debugger support
• Troublesome coding restrictions
• Poor simulator support
• Limited device penetration in the U.S.

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Symbian Python

• Poor performance
• Low learning threshold
• Reasonable UI framework
• Relatively high ceiling
• Poor IDE/debugger support
• Poor simulator support
• Additional runtime overhead (gt 1mb)
• Limited device penetration in the U.S.

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Palm

• Huge paradigm shift between version 1.x 4.x and
  5.x
• Only device specific simulator after 5.x
• Gradually becoming obsolete

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Android and iPhone

• Android
• Customized version of Java (between Java desktop
  and J2ME)
• Good UI framework (when compared with J2ME)
• Limited media capture capability as J2ME
• Calling native functions is discouraged
• iPhone
• HTML AJAX based web app running on browsers
• Native app (Objective C)

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Native Code vs. Dynamic Script

• Native Code
• Excellent runtime speed
• High threshold, high ceiling
• Easy to access the low level hardware
• Difficult to program and difficult to debug
• Dynamic (Interpreted) Script
• Slow runtime speed
• Easy to learn, low ceiling
• Easy to debug, easy to share
• Hard to access extra features of the hardware
• Can we take advantages of nice things from both
  approaches?

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Embedding Scripts to the Host Application
Host Program
color RED b button label OK, x
10, y 20
Embedded Interpreter
Wrapped Library
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Choice of the Embedded Script Engine

• Lua is a powerful, fast, light-weight, embeddable
  scripting language
• Originated in 1993, now developed by Lablua
• Designed as a lightweight embedded script
  language
• A leading scripting language in the games
  industry
• See www.lua.org
• Has been ported to BREW, Windows Mobile and
  Symbian

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Approximate Runtime Performance

• Not intended to be a comprehensive evaluation
• Benchmarking programs (sorting, factorial
  computing, string operations)

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Some Sample Codes
function HelloWorld () io.write ("hello
World") trace ("trace working now")
end HelloWorld()
function fat (n) if n 0 then return 1
else return nfat(n-1) end end
Function max(a, b) local m a if b gt a
then m b end return m end
1 MOVE 2 0 0 R(2) R(0) 2 LT 0 0 1
R(0) lt R(1) 3 JMP 1 to 5 (41) 4
MOVE 2 1 0 R(2) R(1) 5 RETURN 2 2 0
return R(2) 6 RETURN 0 1 0 return
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Easy to Switch Between both Worlds
LIBSHELL_API int LibSHELL_MessageBoxText(lua_State
L) const char szTitle (const char
)luaL_checkudata(L, 1, AECHAR_TNAME) const
char szText ( const char )luaL_checkudata(L,
2, AECHAR_TNAME) ISHELL_MessageBoxText(GETAPPSH
ELL(), szTitle, szText) return
0 lua_register(L, messageBox",
LibSHELL_MessageBoxText)
Exporting the ISHELL_MessageBoxText function from
BREW to the script
Void FireEvent(int id, const char args) if
(g_strEventHandler ! NULL) char
buf254 SPRINTF( buf, s(d,s),
g_strEventHandler, id, args)
lua_pcall(luaState, buf, LUA_MULTRET, 0)
return
Calling a lua function (event handler) from C/C
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Scaffolding Mobile Development via Script
Embedding

• Average users
• Use form-guided code generation templates to
  customize an application
• Download and share new functions
• Group development
• Only one member responsible for C/C
  programming, expose additional native functions
  to script programmers via glue function
• Other members fast prototyping in script
• Runtime performance sensitive application
• Identify performance bottlenecks in the script
  implementation, reemployment them in C/C and
  export them to the script

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Summary

• Building applications for cell phones is
  challenging due to highly diversified environment
  and toolkits
• Trade-offs between low learning threshold and
  high ceiling need to be carefully considered
• Script embedding is a solution to leverage nice
  features from both worlds

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Thanks!

• Any questions?