/**
  * Image Loader for the HF Broadcasr Receiver Demonstrator Applet
  * @author Robert J Morton YE572246C
  * @version 12 Dec 2007 */

import java.awt.*;             // abstract window tool kit for applet 
import java.awt.MediaTracker;  // for the new-fangled 1.1 event handling

public class imgldr {

  private hfbrx_swing hf;    // instance reference to the hfbrx_swing applet
  private messagespanel sm;  // instance reference for message panel

  // to track when the progress of image loading
  private MediaTracker tracker;

  private boolean 
    loadingImages = true,
    trackerError = false,  // true = tracker encountered an error
    loadFTT = true,        // To avoid an erase and repaint of loading and
    errorFTT = true;       // load-error messages every refresh cycle.


  imgldr(hfbrx_swing hf, messagespanel sm) {
    this.hf = hf;  // instance reference to the movmap applet
    this.sm = sm;  // instance of message panel

    //create a media tracker and register images with it
    tracker = new MediaTracker(hf);

    if(hf.JarredImages)  // if loading images from the applet's own jar file
      hf.IMG1 = hf.getImage(getClass().getResource("map.png"));
    else                 // else we're loading images from remote server
      hf.IMG1 = hf.getImage(hf.getDocumentBase(),"map.png"); 

    // add the images to the tracker's watch list
    tracker.addImage(hf.IMG1,0);
  }


  boolean awaitingImages() {
    if(loadFTT) {  // if this is the first time through here
      sm.showMsg("Loading image from server...", false);
      loadFTT = false;  // avoid repeating display every cycle      
    }
    /* Keep checking the tracker for a signal. If the tracker does
    not say anything, return without servicing the applet's thread. */
    try { tracker.waitForAll(); }
    catch (InterruptedException e) { return true; }

    return false;  // will drop thru when tracker gives a completion signal
  }


  boolean imagesLoaded() {
    if(tracker == null)  // Returns true when image
      return true;       // loading has terminated.
    if(loadingImages) {  // if image loading process still running

      // Get the current status of the image loading process.
      int ts = tracker.statusAll(false);

      // If the image loading process has terminated in an error state
      if((ts & MediaTracker.ERRORED) != 0) {
        trackerError = true;  // indicates image loading failure
        if(errorFTT) {        // if this is the first time through here
          sm.showMsg("Error: couldn't load image.", true);
          errorFTT = false;   // avoid repeating display every cycle
        }
      }
      /* if the tracker has completed its task, set flag to
      indicate that the image loading process has terminated. */
      if(ts == MediaTracker.COMPLETE) {
        loadingImages = false;
      }
    } else {          // Else, the image loading process has just finished,
      killTracker();  // so refresh display if this hasn't already been done
      sm.showMsg("Image Loaded.", false);
    }
    return false;
  }


  void killTracker() {
    if(tracker != null) {              // if tracker object still exists
      tracker.removeImage(hf.IMG1,0);  // Remove (de-register) the image 
      tracker = null;                  // from it then kill the tracker
    }
  }


  boolean TrackerError() { return trackerError; }
}