sheep_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.util.Random;
import java.io.IOException;
import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;

public class Sheep_Canvas
    extends GameCanvas
    implements Runnable, CommandListener {

  //代表程序是否运行的状态
  boolean running;

  //存储构成羊动画的各图像帧
  Image sheep_img;

  //存储构成背景的各图像帧
  Image grass_img, fence_img;

  //代表羊动画的精灵对象
  Sprite sp;

  //动画播放序列
  int fs[][] = {
      {
      0, 1, 2, 3, 4}
      , {
      5, 6, 7, 8, 9}
      , {
      10, 11, 12, 13, 14}
  };

  //代表草地背景
  TiledLayer tlg;

  //代表栅栏背景
  TiledLayer tlf;

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

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

  //每帧羊图像的宽高
  int img_sheep_size = 15;

  //每帧草图像的宽高
  int img_grass_size = 16;

  //每帧栅栏图像的宽高
  int img_fence_size = 16;

  //代表羊所处的方位，0、1、2、3分别代表上下左右道路。
  int dir = 2;

  //绘制上下文
  Graphics g = getGraphics();

  //主MIDlet类实例
  Sheep_MIDlet sm;

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

    try {
      sheep_img = Image.createImage("/icons/background/sheep.png");
      grass_img = Image.createImage("/icons/background/grass.png");
      fence_img = Image.createImage("/icons/background/fence.png");
    }
    catch (IOException e) {
      System.out.println(e.getMessage());
    }
    // 计算横向需要多少图片
    int backcols = win_width / img_grass_size + 1;
    // 计算纵向需要多少图片
    int backrows = win_height / img_grass_size + 1;
    //铺草地
    tlg = new TiledLayer(backcols, backrows, grass_img, img_grass_size,
                         img_grass_size);
    Random r = new Random();
    for (int i = 0; i < backcols * backrows; i++) {
      int n = (r.nextInt() >>> 1) % 5 + 1;
      tlg.setCell(i % backcols, i / backcols, n);
    }

    //铺栅栏
    tlf = new TiledLayer(backcols, backrows, fence_img, img_fence_size,
                         img_fence_size);
    //铺外上栅栏
    for (int i = 0; i < backcols; i++) {
      tlf.setCell(i, 0, 1);
    }
    //铺外下栅栏
    for (int i = 0; i < backcols; i++) {
      tlf.setCell(i, backrows - 2, 1);
      tlf.setCell(i, backrows - 1, 1);
    }
    //铺外左栅栏
    for (int i = 0; i < backrows; i++) {
      tlf.setCell(0, i, 1);
    }
    //铺外右栅栏
    for (int i = 0; i < backrows; i++) {
      tlf.setCell(backcols - 2, i, 1);
      tlf.setCell(backcols - 1, i, 1);
    }
    //铺内上栅栏
    for (int i = 2; i < backcols - 3; i++) {
      tlf.setCell(i, 2, 1);
    }
    //铺内下栅栏
    for (int i = 3; i < backcols - 3; i++) {
      tlf.setCell(i, backrows - 4, 1);
    }
    //铺内左栅栏
    for (int i = 2; i < backrows - 3; i++) {
      tlf.setCell(2, i, 1);
    }
    //铺内右栅栏
    for (int i = 3; i < backrows - 3; i++) {
      tlf.setCell(backcols - 4, i, 1);
    }

    //初始化羊
    sp = new Sprite(sheep_img, img_sheep_size, img_sheep_size);
    sp.setFrameSequence(fs[0]);
    sp.setFrame(0);
    sp.setPosition(17, 16 * (backcols - 3));

    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() {
    long st = 0, et = 0, diff = 0;
    //控制每秒帧数，即动画快慢
    int rate = 250;

    while (running) {
      st = System.currentTimeMillis();
      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.实现绘制
   */
  private void render(Graphics g) {
    //绘制背景
    g.setColor(0x000000);
    g.fillRect(0, 0, win_width, win_height);
    tlg.paint(g);
    tlf.paint(g);
    //处理碰撞
    if (sp.collidesWith(tlf, false)) {
      //处理左上角
      if (sp.getX() < 18 && sp.getY() < 17) {
        dir = 0;
        sp.setFrameSequence(fs[1]);
        sp.setTransform(Sprite.TRANS_MIRROR);
        sp.setPosition(17, 17);
      }
      //处理右上角
      if (sp.getX() > ( (win_width / 16 - 2) * 16) && sp.getY() < 18) {
        dir = 3;
        sp.setFrameSequence(fs[2]);
        sp.setTransform(Sprite.TRANS_NONE);
        sp.setPosition( (win_width / 16 - 2) * 16, 17);
      }
      //处理右下角
      if (sp.getX() == ( (win_width / 16 - 2) * 16) &&
          sp.getY() > ( (win_height / 16 - 2) * 16)) {
        dir = 1;
        sp.setFrameSequence(fs[1]);
        sp.setTransform(Sprite.TRANS_NONE);
        sp.setPosition( (win_width / 16 - 2) * 16, (win_height / 16 - 2) * 16);
      }
      //处理左下角
      if (sp.getX() < 17 && sp.getY() == ( (win_height / 16 - 2) * 16)) {
        dir = 2;
        sp.setFrameSequence(fs[0]);
        sp.setTransform(Sprite.TRANS_NONE);
        sp.setPosition(17, (win_height / 16 - 2) * 16);
      }
    }
    //没有碰撞
    else {
      switch (dir) {
        case 0:
          sp.move(3, 0);
          sp.nextFrame();
          break;
        case 1:
          sp.move( -3, 0);
          sp.nextFrame();
          break;
        case 2:
          sp.move(0, -3);
          sp.nextFrame();
          break;
        case 3:
          sp.move(0, 3);
          sp.nextFrame();
          break;
      }

    }
    sp.paint(g);
    flushGraphics();
  }

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

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

}