J2ME%20

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J2ME BREW Game Design

• Code running on the handset (at last)

Greg Costikyan www.ungames.comwww.costik.comcost
ik_at_costik.com
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What is BREW?

• Binary Runtime Environment for Wireless

• Tied to CDMA (in practice, if not theory)
• Strongly supported by Verizon, AlltelKorean
  carriers, KDDI in Japan, Bell Mobility in Canada

• Like Java, runs in a virtual machine (on the
  hardware)

• Qualcomm is the Gatekeeper

• Write apps in C, C, or Java

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What is J2ME?

• Java 2 Micro Edition (for small device
• CLDC Connected Limited Device Configuration
• MIDP Mobile Information Device Profile

• Runs on a virtual machine (KVM, lt80k)

• Java-enabled phones available in Japan, Korea,
  Europe, through Nextel major commitment by
  Sprint, support from all major manufacturers

• Carriers are the Gatekeepers (but Motorola for
  Nextel)

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Which Should You Use?

• Little difference in technical capability

• Largely a business decision

• Likely to be a larger installed base of
  J2ME-enabled handsets

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Why Develop J2ME/BREW Games?

• Run apps on the handset (not all logic has to be
  on the server side)

• Much better control over UI

• Small User Base at Present (but likely to grow
  fast)

• An area of carrier focus

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How it Used to Work

1. Download applet to your PC over the Internet.
2. Hotsynch your phone to install applet.
3. Cant install applications over the air network.
4. In Asia, applets cant communicate over the
   networksoloplay only.

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How it Now Works

1. User makes a network connection, browses
   carriers list of midlets, chooses one.
2. HTTP request goes out over air network, is routed
   to remote server on the Internet.
3. Server sends midlet to handset, where it is
   installed.
4. Network sockets are exposed to J2ME on the
   handset, so midlets can send and receive data
   with remote servers.

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Technical Limitations

• Midlets must be lt50k (or so)

• No simultaneous key presses

• No support for image transparency

• Cannot edit bitmaps on the fly, no blitting

• Cant assume any audio support

• No floating point math

• No JNI or AWT

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What We Can Rely On

• High-Level UI Features
• PNGs bitmaps
• Text Entry
• Select lists (radio buttons) Multiple select
  lists (check boxes)
• Bar graphs
• Support for standard phone keys (0-9, , ,
  arrows)
• Abstracted game controls

• Low-Level UI Features
• Canvas
• Graphics

• HTTP

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Latency gt WAP?

• With WAP, latency air network Internet latency

• With J2ME, add HTTP handshaking

• UDP is supported but not mandatory but exists
  on Motorola/iDen handsets (Nextel)

• An area of carrier focus

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Keep Network Access Sessions Short

• People pay by the minute but YOU get nada

• 5-10 minute sessionsoffline as well as online
  componentssimove, deck construction

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Network Still Unreliable

• Irrelevant for soloplay

• If connection is intermittent, game needs need to
  sense network failure

• If connection continuous, handle drops gracefully

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Dealing with the 50k Limit

• Keep text short

• Use ( reuse) small number of graphics

• Use a code obfuscator

• Minimize the number of inner classes

• Collapse the class hierarchy

• Maximize use of pre-installed classes

• Consider using multiple midlets

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Making the Most of Graphics

• No inherent support for layers

• Tiled Backgrounds (or images at discrete
  locations on blank background)

• Limit number of sprites behaviors

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Thinking About UI

• Handset is similar to a console controller

• Motion for a single actor arcade-style, RPGs

• Select an actor, select a destinationsimple
  strategy games

• Select-lists menus

• 11 buttons NetHack-style UI

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What Kinds of Games Can We Do?

• Primitive skill-and-action games (retro arcade)

• Classic board card

• Console-like games with simple controls (gold,
  driving)

• Levelware

• Networking is STILL where mobile phones have an
  advantage

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Jamdat Bowling
www.jamdatgames.com
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Diamond Mine
www.jamdatgames.com
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Micro Nitro
www.morpheme.co.uk
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Froggy
www.perimind.com
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URLs

• Obfuscatorswww.alphaworks.ibm.com/tech/JAX/ret
  rologic.com
• J2ME Wireless Toolkitjava.sun.com/products/j2mew
  toolkit/
• Useful Articleswireless.java.sun.com/midp/articl
  es/www.gamasutra.com/resource_guide/20010917/fox_
  01.htm