///////    ImageSequence.java    ///////
import java.applet.Applet;
import java.net.URL;
import java.awt.*;

public class ImageSequence
{   public ImageSequence(URL location, String img_file,
                  String ext, int dim, Applet p, Toolkit tk)
    {   pic = new Image[dim];
        app = p;  n = dim;
        tracker = new MediaTracker(app);
     // get annimation frames (id == 0) 
        for (int i = 0; i < n; i++)
        {   pic[i] = (tk != null)
                 ?  tk.getImage(img_file+i+ext) 
                 : app.getImage(location, img_file+i+ext); 
            tracker.addImage(pic[i], 0);                
        }
        tracker.checkID(0, true);   // starts image loading
    }

    protected ImageSequence() {}

// gets next frame, cycling back to 1st frame or not
    public Image next(boolean cycle)
    {  if ( loaded() )                   // waits
       {  if ( ! cycle && index == n-1 ) // end reached
          {  index= -1;  return null; } 
          index = (index+1) % n;
          return pic[index];
       }
       return null;                      // error
    }

    public int width()
    {  if ( loaded() ) 
	   return pic[0].getWidth(null);
       else return -1;
    }

    public int height()
    {  if ( loaded() )
           return pic[0].getHeight(null);
       else return -1;
    }

    private boolean loaded()
    {  if (  ready ) return true;
       try
       {   tracker.waitForID(0);    // loading terminated 
       } catch (InterruptedException e)
         { ERROR = true;  return false; }
    
       if ( tracker.isErrorID(0) )  // check for error
       {   ERROR = true;  return false;  }
       else
           return (ready = true);
    }

    public static boolean ERROR = false;
    protected boolean ready=false;
    protected Applet app;
    protected Image[] pic = null;
    protected int n;
    protected MediaTracker tracker;
    protected int index=-1;
}