import java.awt.*;

import java.awt.event.*;

import java.lang.*;
import java.lang.Math;
import java.text.*;



public class Equilibrium2 extends java.applet.Applet 

  implements Runnable {


  Canvas oscillators;

  Label beamWeightLabel, blackWeightLabel, blackPosLabel, orangePosLabel, 

        bluePosLabel, bluePosS,

        beamWeightS, blackWeightS, blackPosS, orangePosS;

  Thread runner;

  Scrollbar beamWscroll, blackWscroll, blackXscroll, orangeXscroll,

     blueXscroll;
  int beamWeight, blackWeight, blackPos, orangePos, bluePos;

  double beamW, blackW, blackX, orangeX, blueX, blueForce, redForce;



  int[] redExes = new int[3];

  int[] redWhys = new int[3];

  int[] blueExes = new int[3];

  int[] blueWhys = new int[3];

  Image offscreenImg;

  Graphics offscreenG;



  boolean startFlag = false;


  void buildConstraints(GridBagConstraints gbc, int gx, int gy, 

      int gw, int gh,

      int wx, int wy) {

	gbc.gridx = gx;

	gbc.gridy = gy;

	gbc.gridwidth = gw;

	gbc.gridheight = gh;

	gbc.weightx = wx;

	gbc.weighty = wy;

  }



  public void init() {

    GridBagLayout gridbag = new GridBagLayout();

    GridBagConstraints constraints = new GridBagConstraints();

    setLayout(gridbag);



    // beam Weight text

    buildConstraints(constraints, 0, 0, 1, 1, 20, 5);

    constraints.fill = GridBagConstraints.NONE;

    constraints.anchor = GridBagConstraints.EAST;

    Label beamWeightLabel = new Label("Weight of the beam (N):", Label.CENTER);

    gridbag.setConstraints (beamWeightLabel, constraints);

    add(beamWeightLabel);



    // beam Weight scrollbar label

    buildConstraints(constraints, 2, 0, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    beamWeightS = new Label("20", Label.LEFT);

    beamWeight = 20;

    gridbag.setConstraints (beamWeightS, constraints);

    add(beamWeightS);



    // beam Weight scrollbar

    buildConstraints(constraints, 1, 0, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    beamWscroll = new Scrollbar(Scrollbar.HORIZONTAL, 20, 1, 0, 50);

    gridbag.setConstraints (beamWscroll, constraints);

    add(beamWscroll);



    // black Weight text

    buildConstraints(constraints, 0, 1, 1, 1, 20, 5);

    constraints.fill = GridBagConstraints.NONE;

    constraints.anchor = GridBagConstraints.EAST;

    Label blackWeightLabel = new Label("Weight of the black box (N):", Label.CENTER);

    gridbag.setConstraints (blackWeightLabel, constraints);

    add(blackWeightLabel);



    // black Weight scrollbar label

    buildConstraints(constraints, 2, 1, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    blackWeightS = new Label("20", Label.LEFT);

    blackWeight = 20;

    gridbag.setConstraints (blackWeightS, constraints);

    add(blackWeightS);



    // black Weight scrollbar

    buildConstraints(constraints, 1, 1, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    blackWscroll = new Scrollbar(Scrollbar.HORIZONTAL, 20, 1, 0, 50);

    gridbag.setConstraints (blackWscroll, constraints);

    add(blackWscroll);



    // black position text

    buildConstraints(constraints, 0, 2, 1, 1, 20, 5);

    constraints.fill = GridBagConstraints.NONE;

    constraints.anchor = GridBagConstraints.EAST;

    Label blackPosLabel = new Label("Position of the black box (cm):", Label.CENTER);

    gridbag.setConstraints (blackPosLabel, constraints);

    add(blackPosLabel);



    // black position scrollbar label

    buildConstraints(constraints, 2, 2, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    blackPosS = new Label("80", Label.LEFT);

    blackPos = 80;

    gridbag.setConstraints (blackPosS, constraints);

    add(blackPosS);



    // black position scrollbar

    buildConstraints(constraints, 1, 2, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    blackXscroll = new Scrollbar(Scrollbar.HORIZONTAL, 80, 2, 0, 100);

    gridbag.setConstraints (blackXscroll, constraints);

    add(blackXscroll);



    // orange position text

    buildConstraints(constraints, 0, 3, 1, 1, 20, 5);

    constraints.fill = GridBagConstraints.NONE;

    constraints.anchor = GridBagConstraints.EAST;

    Label orangePosLabel = new Label("Position of orange box (cm):", Label.CENTER);

    gridbag.setConstraints (orangePosLabel, constraints);

    add(orangePosLabel);



    // orange position scrollbar label

    buildConstraints(constraints, 2, 3, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    orangePosS = new Label("50", Label.LEFT);

    orangePos = 50;

    gridbag.setConstraints (orangePosS, constraints);

    add(orangePosS);



    // orange position scrollbar

    buildConstraints(constraints, 1, 3, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    orangeXscroll = new Scrollbar(Scrollbar.HORIZONTAL, 50, 2, 0, 100);

    gridbag.setConstraints (orangeXscroll, constraints);

    add(orangeXscroll);



    // blue position text

    buildConstraints(constraints, 0, 4, 1, 1, 20, 5);

    constraints.fill = GridBagConstraints.NONE;

    constraints.anchor = GridBagConstraints.EAST;

    Label bluePosLabel = new Label("Position of blue support (cm):", Label.CENTER);

    gridbag.setConstraints (bluePosLabel, constraints);

    add(bluePosLabel);



    // blue position scrollbar label

    buildConstraints(constraints, 2, 4, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    bluePosS = new Label("80", Label.LEFT);

    bluePos = 80;

    gridbag.setConstraints (bluePosS, constraints);

    add(bluePosS);



    // blue position scrollbar

    buildConstraints(constraints, 1, 4, 1, 1, 20, 0);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    constraints.anchor = GridBagConstraints.WEST;

    blueXscroll = new Scrollbar(Scrollbar.HORIZONTAL, 80, 1, 50, 100);

    gridbag.setConstraints (blueXscroll, constraints);

    add(blueXscroll);



    // canvas

    buildConstraints(constraints, 0, 5, 3, 1, 0, 80);

    constraints.fill = GridBagConstraints.HORIZONTAL;

    oscillators = new Canvas();

    gridbag.setConstraints (oscillators, constraints);

    add(oscillators);



    offscreenImg = createImage(this.size().width, this.size().height);

    offscreenG = offscreenImg.getGraphics();

  }

  public void start() {
    if (runner == null); {
      runner = new Thread(this);
      runner.start();
    }
  }

  public void stop() {
    if (runner != null) {
      runner.stop();
      runner = null;
    }
  }

  public void run() {



    int index;



    while (true) {

      beamW = beamWeight;

      blackW = blackWeight;

      blackX = blackPos;

      orangeX = orangePos;

      blueX = bluePos;



      blueForce = (beamW*30+blackW*(blackX-20)+50*(orangeX-20))/(blueX-20);

      redForce = (beamW*(blueX-50)+blackW*(blueX-blackX)+50*(blueX-orangeX))/(blueX-20);



      redExes[0]=90;

      redExes[1]=82;

      redExes[2]=98;

      redWhys[0]=297;

      redWhys[1]=321;

      redWhys[2]=321;

      

      for (index=0; index <=2; index++) {

           blueExes[index] = redExes[index]+2*(bluePos-20);

           blueWhys[index] = redWhys[index];

      }



     repaint();

     try { Thread.sleep(10); }

     catch (InterruptedException e) { }

     }
  }

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

  public void paint(Graphics g) {



  int i, yVal;



     // Draw background

    offscreenG.setColor(Color.lightGray);

    offscreenG.fillRect(0,0,500,199);

    offscreenG.setColor(Color.white);

    offscreenG.fillRect(0,200,500,200);



   // Draw vectors

    NumberFormat nf = NumberFormat.getInstance();

    nf.setMaximumFractionDigits(4);

    offscreenG.setColor(Color.red);

    offscreenG.drawString("Red support force = " + nf.format(redForce) + " N", 300, 320);

    offscreenG.drawString("Position of red support = 20 cm" , 300, 340);

    offscreenG.fillPolygon(redExes,redWhys,3);

    offscreenG.drawString("WARNING : A negative support force implies" , 50, 360);

    offscreenG.drawString("that the system is unstable and will tip over." , 50, 375);

    offscreenG.setColor(Color.blue);

    offscreenG.drawString("Blue support force = " + nf.format(blueForce) + " N", 300, 360);

    offscreenG.drawString("Position of blue support = " + bluePos + " cm", 300, 380);

    offscreenG.fillPolygon(blueExes,blueWhys,3);

    offscreenG.setColor(Color.gray);

    offscreenG.fillRect(50,280,200,20);

    offscreenG.drawString("Beam weight = " + beamWeight + " N", 300, 220);

    offscreenG.drawString("The beam is 100 cm long", 50, 240);

    offscreenG.setColor(Color.orange);

    offscreenG.fillRect(50+2*orangePos-10,260,20,20);

    offscreenG.drawString("Orange box weighs 50 N", 300, 240);

    offscreenG.drawString("Position of orange box = " + orangePos + " cm", 300, 260);

    offscreenG.setColor(Color.black);

    offscreenG.drawString("Black box weighs " + blackWeight + " N", 300, 280);

    offscreenG.drawString("Position of black box = " + blackPos + " cm", 300, 300);

    offscreenG.fillRect(50+2*blackPos-8,264,16,16);

   g.drawImage(offscreenImg,0,0,this);

  }



  public void destroy() {

     offscreenG.dispose();

  }



  public boolean action (Event evt, Object arg) {



    if (evt.target instanceof Button) {

    }

    else return super.action(evt, arg);

    return true;

  }



  public boolean handleEvent(Event evt) {



    if (evt.target instanceof Scrollbar) {

      if ((Scrollbar)evt.target == beamWscroll) {

        beamWeight = ((Scrollbar)evt.target).getValue();

        beamWeightS.setText(String.valueOf(beamWeight));

      }

      else if ((Scrollbar)evt.target == blackWscroll) {

        blackWeight = ((Scrollbar)evt.target).getValue();

        blackWeightS.setText(String.valueOf(blackWeight));

      }

      else if ((Scrollbar)evt.target == blackXscroll) {

        blackPos = ((Scrollbar)evt.target).getValue();

        blackPosS.setText(String.valueOf(blackPos));

      }

      else if ((Scrollbar)evt.target == orangeXscroll) {

        orangePos = ((Scrollbar)evt.target).getValue();

        orangePosS.setText(String.valueOf(orangePos));

      }

      else if ((Scrollbar)evt.target == blueXscroll) {

        bluePos = ((Scrollbar)evt.target).getValue();

        bluePosS.setText(String.valueOf(bluePos));

      }

	repaint();

    }

    else return super.handleEvent(evt);

    return true;

  }

}