/** Air Navigation Waypoint Intercept Demonstrator 
    by Robert J Morton UK-YE572246C 21 Oct 1997 */

/*  A demonstrator applet for the Waypoint Encounter class: NavEncPG.class
    which in turn uses the classes: Aircraft.class and Waypoint.class */

import java.awt.*;        // abstract window tool kit for applet 
import java.lang.System;  // needed for system time services

public class wpapplet extends java.applet.Applet implements Runnable {

  String            //Field names
    Names[] = {
      "WAYPOINT ENCOUNTER","","Waypoint Name","","Selected Radial",
      "Aircraft Bearing","Radial Deviation","","Station Bearing",
      "Steering Offset","Required Heading","","Distance"
    },

  //leading zeros for displaying numeric values
    Zeros[] = {"","0","00","000"};

  int
    SelRad = -44,  // Selected Radial in angular degrees
    XM = 190,      // x margin between left edge and start of tracking area
    fh,            // font height (height of a line of text)
    fa,            // font ascent (height of letters above base line)
    nw,            // width in pixels of longest field name
    vw,            // width in pixels of standard value string
    NY,            // top margin for start of text
    VY, vy,        // start height of first numeric value
    X=520, Y=200;  // window and image buffer dimensions

  // values from previous pass of update()
  int[] OldVal={999,999,999,999,999,999,999};

  long
    TF = 50,  // inter-plot time frame (milliseconds)
    T;        // future system time at which a new plot is due to begin

  Thread TH;    // declare a program thread reference variable
  aircraft ac;  // reference to an aircraft object
  waypoint wp;  // reference to a waypoint object
  wpencpg  en;  // reference to an encounter object
  wpcolour ca;  // reference to a colour array object

  Color TFC = Color.white;  // text foreground colour

  //reference to a font (or typeface) for the text in this applet
  Font font = new Font("Dialog",Font.PLAIN,12);

  FontMetrics fm;       // reference to the font's dimensions etc.
  Image buffer = null;  // reference for an off-screen image buffer
  Graphics gc = null;   // graphics context for the off-screen image


  public void init() {  // INITIALISE THE APPLET

    // Create the off-screen image buffer and get its graphics context.
    buffer = createImage(X,Y);
    gc = buffer.getGraphics();

    // Fill the off-screen image with the background colour.
    gc.setColor(Color.black);
    gc.fillRect(0,0,X,Y);

    ac = new aircraft();  // create an aircraft object
    wp = new waypoint();  // create a waypoint object
    en = new wpencpg();   // create an encounter object
    ca = new wpcolour();  // create a colour array object

    fm = getFontMetrics(font);  // get the dimensions etc for this font
    fh = fm.getHeight();        // get the full height of a line of text
    fh = 14;                    // Netscape Navigator problem
    fa = fm.getAscent();        // get the font's ascent (ht above baseline)
    fa = 10;                    // Netscape Navigator problem

    // width of the longest field name + 10pixels
    nw = fm.stringWidth(Names[10]) + 20;

    vw = fm.stringWidth("000+");  // width of numeric value readout string
    NY = 5;                       // top 'margin' for text

    // starting height of first numeric value field
    VY = NY + fh + fh + fh + fh;

    // Set System Time at which the first time frame will terminate.
    T = System.currentTimeMillis() + TF;
  }


  private void reset(){  // PAINT THE SUPERSTRUCTURE FOR A NEW RUN

    /* Clear the text area by filling it with its background colour
    then set up the text area's font to print in white lettering. */

    gc.setColor(Color.black);
    gc.fillRect(0,0,XM,ca.YH);
    gc.setFont(font);
    gc.setColor(Color.white);

    int y = NY;  // Set the vertical start position for the text.

    /* Display each of the 13 Field Names, each on a separate line,
    additionally showing the waypoint's name on the third line. */

    for(int i = 0 ; i < 13 ; i++) {
      gc.drawString(Names[i], 10, y += fh);
      if(i == 2) gc.drawString(wp.N, nw, y);
    }

    // For each line of pixels in the map area ...
    for(y = 0 ; y < ca.YH ; y++) {
      int
        X = 0,  // starting dot of next single-colour stretch of line
        x = 0;  // to find next pixel in current line with a different colour 

      // Make the colour of the first dot the reference colour.
      Color c = ca.C[X][y];

      // While we've not yet reached the end of the current line of pixels
      while(++x < ca.XW) {

        /* If this dot's a different colour from previous dot, set the colour
        to that of the previous dot, draw the line from the start dot to the
        previous dot then make the new reference colour that of this dot. */

        if(c != ca.C[x][y]) {
          gc.setColor(c);
          gc.drawLine(XM + X,ca.YH - y - 1,XM + x - 1,ca.YH - y - 1);
          c = ca.C[X = x][y];
        }
      }

      /* Set the colour for the final stretch of the
      current line, then draw the the final stretch. */

      gc.setColor(c);
      gc.drawLine(XM + X,ca.YH - y - 1,XM + x - 1,ca.YH - y - 1);
    }
    repaint();  // re-display the off-screen image
  }


  //PAINT THE INITIAL IMAGE from the off-screen image buffer
  public void paint(Graphics g) { g.drawImage(buffer, 0, 0, null); }


  //PAINT THE IMAGE SO FAR from the off-screen image buffer
  public void update(Graphics g) { g.drawImage(buffer, 0, 0, null); }


  // DISPLAY A NUMERIC VALUE FOR A FIELD ON THE OFF-SCREEN IMAGE
  void ShowNum(Graphics g,double a,int n){
    if(n < 6)          // If displaying a field that contains an angular
      a *= en.DegRad;  // value, convert the value from radians to degrees.

    String sign;       // Create a string containing sign of integer 'a'.
    if(a < 0) {
      sign = "-";
      a = -a;
    } else
      sign = "+";

    int i = (int)a;    // convert it to an integer and round it off
    if((a -= i) > .5)
      i++;

    vy += fh;          // advance downwards to new text line

    if(i != OldVal[n]){  // if this value has changed since the last update

      /* Remember this time's (changed) value for
      next time then convert it to a String. */

      OldVal[n] = i;
      String s = String.valueOf(i);

      // Compute the number of leading zeros required.
      i = 3 - s.length();
      if(i < 0) i = 0;

      /* Set to background colour and wipe the numeric field's display
      area then set to foreground colour and display the string. */

      gc.setColor(Color.black);
      gc.fillRect(nw,vy - fa,vw,fh);
      gc.setColor(Color.white);
      gc.drawString(Zeros[i] + s + sign,nw,vy);
    }
  }

  void advance() {  // ADVANCE THE AIRCRAFT ALONG THE TRACK

    int  // current 'window co-ordinates' of aircraft
      x = (int)(ac.x + XM),
      y = (int)(ca.YH - ac.y);

    gc.setColor(ca.ATC);      // Set the colour of the aircraft track
    gc.drawLine(x, y, x, y);  // and draw the next bit of it.

    vy = VY;  // set vertical start position of first numeric field

    gc.setFont(font);  // activate the chosen font and then display...

    ShowNum(gc,en.OSR,0);     // outbound selected radial
    ShowNum(gc,en.tBrg,1);    // bearing of aircraft from waypoint
    ShowNum(gc,en.RadDev,2);  // aircraft's deviation from the
                                // selected outbound radial
    vy += fh;  // miss a line

    ShowNum(gc, en.rBrg,3);    // bearing of waypoint from aircraft
    ShowNum(gc, en.StrOff,4);  // steering offset
    ShowNum(gc, en.ReqHdg,5);  // required heading

    vy += fh;  // miss a line

    // Show distance 'to' waypoint as negative and 'from' it as positive. 
    double a = en.Dst;
    if(en.approach)
      a =- a;
    ShowNum(gc,a,6);

    repaint();  // re-display the off-screen image
  }

  public void run() {    // RUN THE WAYPOINT ENCOUNTER PROGRAM THREAD
    while(TH != null) {  // while the run() thread remaims alive...

     // if aircraft has just passed out of range ...
     if(en.outofRange(ac, wp)) {

       // if selected radial has come full circle, start over
       if((SelRad += 44) > 359)
         SelRad -= 360;

       /* Set up the new selected radial, initialise the colour
       array and initialise a new fly-past of the waypoint. */

       en.SetRadial(ac,wp,SelRad);
       ca.InitC(ac,wp,en.OSR);
       reset();
     } else              // Else, plot the aircraft's new 
       ca.PlotPosn(ac);  // position on the display raster

     advance();  // advance the aircraft along its track

     /* Get time remaining in this Time Frame, imposing upon it a lower
     limit of 5 milliseconds, then put thread to sleep for this amount
     of time. Catch any exceptions that may occur while thread is asleep
     but do nothing about them because they are normal external events. */

     long s = T - System.currentTimeMillis();
     if(s < 5) s = 5;
     try{ TH.sleep(s); }
     catch(InterruptedException e) { }

     // Set the System Time at which the next time frame will terminate.
      T = System.currentTimeMillis() + TF;
    }
  }


  /* START THE PROGRAM THREAD by creating the thread object
  and starting it running by requesting a call to run(). */

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

  public void stop() { TH = null; }   // STOP THIS PROGRAM THREAD
}