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在J2me游戏使用“精灵”-Sprite(图)


  Sprite,精灵,顾名思义,专用来代表游戏中的动画角色,比如飞机,坦克等等。在MIDP1.0中,我们必须自己写专门的类来实现Sprite,幸运的是,MIDP2.0为Sprite提供了强力支持,可以创建静态,动态,不透明和透明的Sprite,下面我们准备在上次的GameCanvas基础上添加一个Sprite并让它动起来。
  
  Sprite的主要构造方法有:
  
  Sprite(Image):构造一个单幅图案的Sprite;
  
  Sprite(Image, int width, int height):构造一个动画Sprite,图片将按照指定大小被分为N个Frame,通过setFrame(int index)就可以让Sprite动起来。我们用了一个有透明背景的png图片创建坦克的Sprite:
  
 

  (注意这个图是放大的JPG格式,你需要用Photoshop之类的软件处理成有透明背景的png格式,大小为64x16)
  
  我们在Eclipse中建立如下工程和目录:
  
 

  以下是画出Sprite的TankGameCanvas.java:
  
  package tank.midp.core;import javax.microedition.lcdui.*;import javax.microedition.lcdui.game.*;public class TankGameCanvas extends GameCanvas implements Runnable {  // 控制方向:  private static int INDEX_OF_UP = 0;  private static int INDEX_OF_DOWN = 1;  private static int INDEX_OF_LEFT = 3;  private static int INDEX_OF_RIGHT = 2;  private boolean isPlay; // Game Loop runs when isPlay is true  private long delay; // To give thread consistency  private int currentX, currentY; // To hold current position of the 'X'  private int width; // To hold screen width  private int height; // To hold screen height  private Sprite spriteTank; // our sprite!  // Constructor and initialization  public TankGameCanvas() {    super(true);    width = getWidth();    height = getHeight();    currentX = width / 2;    currentY = height / 2;    delay = 20;    // init sprite:    try {      Image image = Image.createImage("/res/img/player1.png"); // 注意路径      spriteTank = new Sprite(image, 16, 16); // 大小是16x16    }    catch(Exception e) { e.printStackTrace(); }  }  // Automatically start thread for game loop  public void start() {    isPlay = true;    new Thread(this).start();  }  public void stop() { isPlay = false; }  // Main Game Loop  public void run() {    Graphics g = getGraphics();    while (isPlay) {      input();      drawScreen(g);      try {        Thread.sleep(delay);      }      catch (InterruptedException ie) {}    }  }  // Method to Handle User Inputs  private void input() {    int keyStates = getKeyStates();    // Left    if ((keyStates & LEFT_PRESSED) != 0) {      currentX = Math.max(0, currentX - 1);      spriteTank.setFrame(INDEX_OF_LEFT);    }    // Right    if ((keyStates & RIGHT_PRESSED) !=0 ) {      if ( currentX + 5 < width)        currentX = Math.min(width, currentX + 1);      spriteTank.setFrame(INDEX_OF_RIGHT);    }    // Up    if ((keyStates & UP_PRESSED) != 0) {      currentY = Math.max(0, currentY - 1);      spriteTank.setFrame(INDEX_OF_UP);    }    // Down    if ((keyStates & DOWN_PRESSED) !=0) {      if ( currentY + 10 < height)        currentY = Math.min(height, currentY + 1);      spriteTank.setFrame(INDEX_OF_DOWN);    }  }  // Method to Display Graphics  private void drawScreen(Graphics g) {    g.setColor(0); // black    g.fillRect(0, 0, getWidth(), getHeight());    // 画一个Sprite非常简单:    spriteTank.setPosition(currentX, currentY);    spriteTank.paint(g);    flushGraphics();  }}
  
  运行后的画面如下,可以用上下左右控制坦克:
  
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