/** Draw Spring
  dX
 ---- = a v
  dt

  dv
 ---- = - b (v + x)
  dt

横軸 x すなわち位置と、縦軸 v すなわち速度との相図

あるいは、
    2
   d x      dx
m ---- + v ---- + kx = 0
   dt       dt 
**/
import java.awt.*;
import java.applet.*;

public class Spring extends Applet {
  SpringGraph phaseCanvas;
  Panel PrmPanel, InitPanel, CntrlPanel, InputPanel;

  TextField TFalpha, TFbeta, TFinitX, TFinitV;
  double alpha=1.0, beta=0.1, initX = 3.0, initV = -2.0;

  public void init() {
    setLayout(new BorderLayout());

    PrmPanel = new Panel();
    PrmPanel.setLayout(new FlowLayout());
    PrmPanel.add(new Label("alpha=", Label.RIGHT));
    PrmPanel.add(TFalpha = new TextField(String.valueOf(alpha), 4));
    PrmPanel.add(new Label(" beta=", Label.RIGHT));
    PrmPanel.add(TFbeta = new TextField(String.valueOf(beta), 4));

    InitPanel = new Panel();
    InitPanel.setLayout(new FlowLayout());
    InitPanel.add(new Label("Initial value X=", Label.RIGHT));
    InitPanel.add(TFinitX = new TextField(String.valueOf(initX), 4));
    InitPanel.add(new Label("      V=", Label.RIGHT));
    InitPanel.add(TFinitV = new TextField(String.valueOf(initV), 4));

    CntrlPanel = new Panel();
    CntrlPanel.setLayout(new FlowLayout());
    CntrlPanel.add(new Button("Start"));
    CntrlPanel.add(new Button("Stop"));
    CntrlPanel.add(new Button("Clear"));

    InputPanel = new Panel();
    InputPanel.setLayout(new GridLayout(3,1));
    InputPanel.add(PrmPanel);
    InputPanel.add(InitPanel);
    InputPanel.add(CntrlPanel);

    add("Center", phaseCanvas = new SpringGraph(alpha, beta, initX, initV));
    add("South",  InputPanel);
  }

  public boolean action(Event ev, Object arg) {
    if (ev.target instanceof TextField) {
      alpha = Float.valueOf(TFalpha.getText().trim()).floatValue();
      beta  = Float.valueOf(TFbeta.getText().trim()).floatValue();
      initX = Float.valueOf(TFinitX.getText().trim()).floatValue();
      initV = Float.valueOf(TFinitV.getText().trim()).floatValue();
      phaseCanvas.setparam(alpha, beta, initX, initV);
      return true;
    } else if (ev.target instanceof Button){
      String l = ((Button)ev.target).getLabel();
      if ( "Start".equals(l) ){
	alpha = Float.valueOf(TFalpha.getText().trim()).floatValue();
	beta  = Float.valueOf(TFbeta.getText().trim()).floatValue();
	initX = Float.valueOf(TFinitX.getText().trim()).floatValue();
	initV = Float.valueOf(TFinitV.getText().trim()).floatValue();
	phaseCanvas.setparam(alpha, beta, initX, initV);
	phaseCanvas.clear();
	phaseCanvas.start();
      } else if ( "Stop".equals(l) ){
	phaseCanvas.stop();
      } else if ( "Clear".equals(l) ){
	phaseCanvas.clear();
      }
      return true;
    } else 
      return true;
  }

  public boolean handleEvent(Event e) {
    if (e.id == Event.WINDOW_DESTROY) {
      stop();
      destroy();
      System.exit(0);
      return true;
    } else {
      return super.handleEvent(e);
    }
  }

  public static void main(String args[]) {
    PFrame f = new PFrame("Spring Phase Diagram");
    Spring spring = new Spring();
    spring.init();
    spring.start();
    f.add("Center", spring);
    f.resize(450, 500);
    f.show();
  }
}

class PFrame extends Frame {
  PFrame(String title) {
    super(title);
  }

  public boolean handleEvent(Event e) {
    if (e.id == Event.WINDOW_DESTROY) {
      dispose();
      System.exit(0);
    }
    return false;
  }
}
    
class SpringGraph extends Canvas implements Runnable {
  Point A = new Point(0,0), B = new Point(0,0);
  Point O = new Point(0,0);
  Point U = new Point(20,20);
  //  Point U = new Point(8,8);
  static int Height, Width;

  static double alpha, beta, initX, initV;
  static double x, v, dx, dv, T, dt;
  Thread th;
  static boolean clrflg = false;

  public void init() {
    if (th == null){
      th = new Thread(this);
      T = 0.0;
    }
  }

  public void start() {
    if (th == null) {
      th = new Thread(this);
      th.start();
    } else 
      th.resume();
  }

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

  public void run() {
    while (true) {
      try {
	Thread.sleep(100);
      } catch (InterruptedException e) {
	break;
      }
      repaint();
    }
  }

  public void update(Graphics g) {
    if ( clrflg ){
      g.setColor(getBackground());
      g.fillRect(0, 0, Width, Height);
      g.setColor(getForeground());
      clrflg = false;
    }
    paint(g);
  }

  public void clear() {
    clrflg = true;
  }

  SpringGraph(double alpha, double beta, double initX, double initY){
    T = 0.0;
    this.alpha = alpha;
    this.beta  = beta;
    this.initX = initX;
    this.initV = initV;
    x = initX; v = initV;
    aw2px(A, x, v);
  }

  public void setparam(double alpha, double beta, double initX, double initV){
    this.alpha = alpha;
    this.beta  = beta;
    this.initX = initX;
    this.initV = initV;
    x = initX; v = initV;
    aw2px(A, x, v);
  }

  public void aw2px(Point t, double x, double v){
    t.x = (int)(   x * (double)U.x + (double)O.x );
    t.y = (int)( - v * (double)U.y + (double)O.y );
  }

  public void draw_coordinate(Graphics g) {
    g.setColor(Color.pink);
    for (int i = -10; i <= 10; i++) {
      aw2px(A, -10,i);  aw2px(B,  10,i);
      g.drawLine(A.x, A.y, B.x, B.y);
    }
    for (int i = -10; i <= 10; i++) {
      aw2px(A, i,-10);  aw2px(B, i, 10);
      g.drawLine(A.x, A.y, B.x, B.y);
    }

    g.setColor(Color.black);
    aw2px(A,0,-10); aw2px(B,0, 10);
    g.drawLine(A.x, A.y, B.x, B.y);
    aw2px(A,-10,0); aw2px(B,10,0);
    g.drawLine(A.x, A.y, B.x, B.y);
  }

  public void paint(Graphics g) {
    Height = size().height;
    Width  = size().width;
    O.x = Height / 2;
    O.y = Width  / 2;
    draw_coordinate(g);

    g.setColor(Color.blue);

    double tt = T + 1.0, dt = 0.01;
    while ( T <= tt ) {
      aw2px(A, x, v);
      dx =  ( alpha * v) * dt;
      dv =  - beta * ( x + v) * dt;
      x += dx;
      v += dv;
      aw2px(B, x, v);
      g.drawLine(A.x, A.y, B.x, B.y);
      T += dt;
    }
  }
}