// 程序名PigCanvas.java
// 一個(gè)簡單的Canvas的子類和一個(gè)Pig類
import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class PigCanvas extends Canvas {
  private UI_Low9 midlet;
  private Pig pig; //聲明一個(gè)Pig對(duì)象

  public PigCanvas(UI_Low9 midlet ){
    this.midlet = midlet;
    pig = new Pig();
    pig.changeVelocity(3); //設(shè)置pig的行進(jìn)速度，以象素為單位
  } 
 
  protected void paint( Graphics g ){
    //g.translate(getWidth()/2,getHeight()/2);//設(shè)置當(dāng)前坐標(biāo)系統(tǒng)
    g.setColor(0,255,0);
    g.fillRect( 0, 0, getWidth(), getHeight()); //繪制背景
    pig.paint(g); //繪制Pig
  }
  
  protected void keyPressed (int keyCode) { //按鍵事件
    switch (getGameAction(keyCode)) {
      case UP : { //響應(yīng)游戲動(dòng)作UP，執(zhí)行一定的動(dòng)作后然后發(fā)出重畫請(qǐng)求
        pig.goUp();
        repaint();
        break;
      }
      case DOWN : { //響應(yīng)游戲動(dòng)作DOWN，執(zhí)行一定的動(dòng)作后然后發(fā)出重畫請(qǐng)求
        pig.goDown();
        repaint();
        break;
      }
      case LEFT : { //響應(yīng)游戲動(dòng)作LEFT，執(zhí)行一定的動(dòng)作后然后發(fā)出重畫請(qǐng)求
        pig.goLeft();
        repaint();
        break;
      }
      case RIGHT : { //響應(yīng)游戲動(dòng)作RIGHT，執(zhí)行一定的動(dòng)作后然后發(fā)出重畫請(qǐng)求
        pig.goRight();
        repaint();
        break;
      }
      default : { //按其它按鍵，退出應(yīng)用程序
        midlet.exit(); //exit()類方法MIDlet的子類中實(shí)現(xiàn)，用于終止程序
      }
    }
  }
}

class Pig { //一個(gè)Pig類，用作動(dòng)畫中運(yùn)動(dòng)的對(duì)象，這里實(shí)現(xiàn)盡量簡單，目的是為了讀者理解
  private int x,y; //用作絕對(duì)坐標(biāo)
  private int velocity; //物體行進(jìn)速度，單位為象素
  private Image image;
  
  Pig() { //構(gòu)造函數(shù)，并設(shè)置初始值
    x = 0; //設(shè)置當(dāng)前絕對(duì)坐標(biāo)為(0,0)
    y = 0;
    velocity = 1; //設(shè)置速度為1
    image = Image.createImage(22,22);
    Graphics g = image.getGraphics();
    g.setColor(0x0000FF00);
    g.fillRect(0,0,22,22); //在當(dāng)前坐標(biāo)系統(tǒng)中繪制
    g.setColor(0x00000000);
    g.fillRect(2,2,22,22); //在當(dāng)前坐標(biāo)系統(tǒng)中繪制
    g.setColor(0x00F9D3D3);
    g.fillRect(0,0,20,20);
  }
  
  public void changeVelocity(int v) { //用于設(shè)置物體行進(jìn)速度
    if ((v >=0) & (v <10)) {
      velocity = v;
    }
  }
  
  public void pigAt(int x,int y) { //用于設(shè)置物體的絕對(duì)坐標(biāo)
    this.x = x;
    this.y = y;
  }
  
  public void goUp() { //如果物體向上運(yùn)動(dòng)，絕對(duì)坐標(biāo)y減少一個(gè)單位(velocity)
    y -= velocity;
  }
  
  public void goDown() { //如果物體向下運(yùn)動(dòng)，絕對(duì)坐標(biāo)y增加一個(gè)單位(velocity)
    y += velocity;
  }
  
  public void goLeft() { //如果物體向左運(yùn)動(dòng)，絕對(duì)坐標(biāo)x減少一個(gè)單位(velocity)
    x -= velocity;
  }
  
  public void goRight() { //如果物體向右運(yùn)動(dòng)，絕對(duì)坐標(biāo)x增加一個(gè)單位(velocity)
    x += velocity;
  }
  
  public void paint(Graphics g) {
    g.translate(x - g.getTranslateX(), y - g.getTranslateY());//設(shè)置當(dāng)前坐標(biāo)系統(tǒng)
    g.drawImage(image,0,0,g.TOP | g.LEFT);
    g.translate(x - g.getTranslateX(), y - g.getTranslateY());//改回原來的坐標(biāo)系統(tǒng)
  }
}