// 程序：復合型移動
// 范例文件：AI3.java

import java.awt.*;
import java.util.*;
import java.applet.*;
import java.awt.event.*;

class Sprite
{
   int    spriteX,spriteY,VX,VY,AppletWidth,AppletHeight,CurrentMode;
   AI3    Game;
   Random R;

   public Sprite(AI3 Game,int AppletWidth,int AppletHeight)
   {
      this.Game         = Game; 
      this.AppletWidth  = AppletWidth;
      this.AppletHeight = AppletHeight;
      R                 = new Random();
      CurrentMode       = 0;

      spriteX   = 0;
      spriteY   = 0;
      VX        = 0;
      VY        = 0;
   }

   public void updateState()
   {
      if(Math.abs(R.nextInt() % 100) < 5) 
      {
         if(CurrentMode == 0)
            CurrentMode = 1;
         else
            CurrentMode = 0;
      }


      switch(CurrentMode)
      {
         case 0:
                 if(spriteX + 25 > Game.getX())
                    VX = 1;
                 else if(spriteX + 25 < Game.getX())
                    VX = -1;
                 else
                    VX = 0;

                 if(spriteY + 25 > Game.getY())
                    VY = 1;
                 else if(spriteY + 25 < Game.getY())
                    VY = -1;
                 else
                    VY = 0;
                 break;
         case 1: 
                 if(spriteX + 25 > Game.getX())
                    VX = -1;
                 else if(spriteX + 25 < Game.getX())
                    VX = 1;
                 else
                    VX = 0;

                 if(spriteY + 25 > Game.getY())
                    VY = -1;
                 else if(spriteY + 25 < Game.getY())
                    VY = 1;
                 else
                    VY = 0;
                 break;         
      }   
 
      spriteX = spriteX + VX;
      spriteY = spriteY + VY;

      if(spriteX < 0)
         spriteX = 0;
      else if(spriteX > AppletWidth - 50)
         spriteX = AppletWidth - 50;

      if(spriteY < 0)
         spriteY = 0;
      else if(spriteY > AppletHeight - 50)
         spriteY = AppletWidth - 50;
   }

   public void paintSprite(Graphics g)
   {  

      g.setColor(Color.black);           
      g.fillOval(spriteX,spriteY,50,50);
      
      g.setColor(Color.white);
      g.drawLine(spriteX + 25,spriteY + 15,spriteX + 25,spriteY + 35);
      g.drawLine(spriteX + 15,spriteY + 25,spriteX + 35,spriteY + 25);
   }
}

public class AI3 extends Applet 
       implements Runnable,MouseListener,MouseMotionListener
{
   int      mouseX,mouseY,AppletWidth,AppletHeight;   
   Image    OffScreen;
   Thread   newThread; 
   Graphics drawOffScreen;
   boolean  update;
 
   Sprite   S;

   public void init()
   {
      mouseX       = 0;
      mouseY       = 0;
      AppletWidth  = getSize().width;
      AppletHeight = getSize().height;
      update       = false;

      S            = new Sprite(this,AppletWidth,AppletHeight);

      addMouseListener(this);      
      addMouseMotionListener(this);

      OffScreen      = createImage(AppletWidth,AppletHeight);
      drawOffScreen  = OffScreen.getGraphics();
   }

   public void start()        
   {
      newThread = new Thread(this);  
      newThread.start();
   }

   public void stop()      
   {
      newThread = null;       
   }

   public void paint(Graphics g)
   {

      drawOffScreen.clearRect(0,0,AppletWidth,AppletHeight);


      S.paintSprite(drawOffScreen);
           

      g.drawImage(OffScreen,0,0,this); 
   }

   public void update(Graphics g)    
   {
      paint(g);     
   }

   public void run()
   {
      while(newThread != null)
      {
         repaint();  

         try
         {
            Thread.sleep(33);
         }
         catch(InterruptedException E){ }

         if(update)
            S.updateState();    
      }
   }


   public int getX()  
   {
      return mouseX;
   }

   public int getY()  
   {
      return mouseY;
   }


   public void mouseExited(MouseEvent e) 
   {
      update = false;    
   }
   
   public void mouseClicked(MouseEvent e){} 
   
   public void mouseEntered(MouseEvent e)  
   {
      update = true;     
   }
   
   public void mousePressed(MouseEvent e){} 
   
   public void mouseReleased(MouseEvent e){} 
  
   public void mouseMoved(MouseEvent e) 
   {
      mouseX = e.getX();  
      mouseY = e.getY();  
      showStatus("(" + mouseX + "," + mouseY + ")");
   }  
 
   public void mouseDragged(MouseEvent e){}
}