plane_canvas.java

本光盘是《J2ME无线移动游戏开发》一书的配套光盘

package ch08;

import java.io.IOException;
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;

public class Plane_Canvas
    extends GameCanvas
    implements Runnable, CommandListener {

  //代表程序是否运行的状态
  boolean running;

  //存储构成动画的各图像帧
  Image img;

  //代表动画的精灵对象
  Sprite sp;

  //屏幕宽度
  int win_width = getWidth();

  //屏幕高度
  int win_height = getHeight();

  //每帧图像的宽度
  int img_width = 24;

  //每帧图像的高度
  int img_height = 24;

  //主MIDlet类实例
  Plane_MIDlet pm;

  /*
   3.构造器
   */
  public Plane_Canvas(Plane_MIDlet pm) {
    super(true);
    this.pm = pm;
    Command exitCommand = new Command("退出", Command.EXIT, 0);
    addCommand(exitCommand);
    setCommandListener(this);

    try {
      img = Image.createImage("/icons/background/plane.png");
    }
    catch (IOException e) {
      System.out.println(e.getMessage());
    }
    sp = new Sprite(img, img_width, img_height);
    sp.setFrame(0);
    int x = (win_width - img_width) / 2;
    int y = (win_height - img_height) / 2;
    sp.setPosition(x, y);
    start();
  }

  /*
   4.启动线程
   */
  public void start() {
    running = true;
    Thread t = new Thread(this);
    t.start();
  }

  /*
   5.控制进程
   */
  public void run() {
    Graphics g = getGraphics();
    long st = 0, et = 0, diff = 0;
    //控制每秒帧数，即动画快慢
    int rate = 50;
    while (running) {
      st = System.currentTimeMillis();
      GameKeyInput();
      render(g);
      et = System.currentTimeMillis();
      //避免刷新过快，暂停线程至要求帧数
      diff = et - st;
      if (diff < rate) {
        try {
          Thread.sleep(rate - diff);
        }
        catch (InterruptedException ex) {
          stop();
        }
      }

    }
  }

  /*
   6.响应按键
   */
  private void GameKeyInput() {
    //保证左右移动停止后，恢复正向图像帧
    sp.setFrame(0);
    int KeyState = getKeyStates(); // 获得当前按键状态
    // 根据按键状态，飞机图象做相对移动，并判断是否超出屏幕边界
    if ( (KeyState & UP_PRESSED) != 0) { // 上
      if (sp.getY() - 3 < 0) {
        sp.move(0, 0 - sp.getY()); //出边界的处理
      }
      else {
        sp.move(0, -3); //正常处理
      }
      sp.setFrame(0);
    }
    if ( (KeyState & DOWN_PRESSED) != 0) { // 下
      if (sp.getY() + 3 + sp.getHeight() > win_height) {
        sp.move(0, win_height - sp.getY() - sp.getHeight());
      }
      else {
        sp.move(0, 3);
      }
      sp.setFrame(0);
    }
    if ( (KeyState & LEFT_PRESSED) != 0) { // 左
      if (sp.getX() - 3 < 0) {
        sp.move(0 - sp.getX(), 0);
      }
      else {
        sp.move( -3, 0);
      }
      sp.setFrame(1);
    }
    if ( (KeyState & RIGHT_PRESSED) != 0) { // 右
      if (sp.getX() + 3 + sp.getWidth() > win_width) {
        sp.move(win_width - sp.getX() - sp.getWidth(), 0);
      }
      else {
        sp.move(3, 0);
      }
      sp.setFrame(2);
    }

  }

  /*
   7.实现绘制
   */
  private void render(Graphics g) {
    g.setColor(0x000000);
    g.fillRect(0, 0, win_width, win_height);

    sp.paint(g);

    flushGraphics();
  }

  /*
   8.结束线程
   */
  public void stop() {
    running = false;
  }

  /*
   9.响应按钮事件
   */
  public void commandAction(Command c, Displayable s) {
    if (c.getCommandType() == Command.EXIT) {
      pm.quitApp();
    }
  }

}