Writing Java ME Games

What Kind of Games?

Old-skool games.

• Think: 2D, top-down or side-scrollers. "platform games"
• Pixel-drawn characters on large maps
• Super Mario Bros.
• Legend of Zelda
• Metroid
• etc.

Game Dev concepts

Data: Sprites

• Small images representing a single frame of a character
• Often one or two fixed sizes
• Usually lots of sprites stored in one image

Game Dev concepts

Data: Sprites

• Frames are changed out in sequence to animate.

=> { 0, 1, 2, 1 } =>

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Game Dev concepts

Data: What we need in a map

• Maps are huge, scrollable images
• Need to specify interaction details (e.g. collisions, lava, doors, etc)
• Very limited storage and memory
• Want to view only a small viewport at any time

Game Dev concepts

Data: Map Tiles

The Java ME Game API

javax.microedition.lcdui.game

• Layer
• Sprite
• TiledLayer
• LayerManager
• GameCanvas

javax.microedition.lcdui.game.Sprite

javax.microedition.lcdui.game.TiledLayer

javax.microedition.lcdui.game.LayerManager

TileTest!

Game Dev concepts

Gameplay mechanics - A Simple Game Loop

• User input
• All the gameplay excitement
• AI
• Physics
• Animations
• Frequent screen updates

Multithreaded Game Engine

Gameplay mechanics

    public void run()
    {
      while (! _gameOver)
      {
        updateWorld();    // move player, creatures, projectiles, etc.
        checkGameState(); // check for game over, goal achieved, etc
        delay();          // maintain a consistent FPS
      }
    }
    

Our Object Heirarchy

• Sprite
  X,Y
  width,height
• Creature
  abstract move()
• Player
  move() { (Key Input) }
• Enemy
  move() { (AI) }

Canvas++

javax.microedition.lcdui.game.GameCanvas

• Same functionality as Canvas
• + getKeyStates
• + Double Buffering

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Multiple background layers, all moving at different speeds.

GameTest

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Other stuff: Sound (Just my opnion, but...)

• Inconsistent APIs
• Various sound formats supported
• Suspend/Resume problems
• Players don't want it*

*But everyone who won't play your game does.**

**Which means you'll probably have to do it.

Other stuff: Java ME Porting Terror

• Some (many) devices don't double-buffer
• Watch out for the FIRE key event
• One Canvas to rule them all
• Trust nobody!

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