/** 
 * rungekutta.java
 *
 * Title:			rungekutta
 * worked on problem with Dan Chak
 */

package rungekutta;

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

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

// IMPORTANT: Source code between BEGIN/END comment pair will be regenerated
// every time the form is saved. All manual changes will be overwritten.
// BEGIN GENERATED CODE
	// member declarations
// END GENERATED CODE

	boolean isStandalone = false;
	Dimension size;
    
    Image buffer;                    						// The off-screen image for double-buffering
    Graphics bufferGraphics;         						// A Graphics object for the buffer
    Thread animator;                 						// Thread that performs the animation
    boolean please_stop;   
	
	float stepper = 0;
	
	float[] yStart = new float[2];
	
	float dt;
	float t;
	float stopt;

	float[] yEnd = new float[2];;
	
	int last_x;
	int last_y;
	int last_mx;
	int last_my;
	
	int colCount;
	Color[] col = new Color[100];
	boolean clear;

	public rungekutta() {
	}

	public float[] calculate(float h, float xStart, float yStart[], float yEnd[]) 
	{	
		float[] k1 = new float[2];
 		float[] k2 = new float[2];
  		float[] k3 = new float[2];
  		float[] k4 = new float[2];

  		float[] dydxk1 = new float[2];
  		float[] dydxk2 = new float[2];
  		float[] dydxk3 = new float[2];
  		float[] dydxk4 = new float[2];

  		float[] yStartk2 = new float[2];
  		float[] yStartk3 = new float[2];
  		float[] yStartk4 = new float[2];

		  // calculate k1 = h * f(x, y(x))
		  // find f(x, y(x))
		  dydxk1 = dydx(xStart, yStart, dydxk1);
		  for (int i = 0; i < 2; i++) {
		    k1[i] = h * dydxk1[i];
		  }

		  // calculate k2 = h * f(x + h/2, y(x) + k1/2)
		  // find f(x + h/2, y(x) + k1/2)
		  for (int i = 0; i < 2; i++) {
		    yStartk2[i] = yStart[i] + k1[i] / 2.0f;
		  }
		  dydxk2 = dydx(xStart + h/2.0f, yStartk2, dydxk2);
		  for (int i = 0; i < 2; i++) {
		    k2[i] = h * dydxk2[i];
		  }

		  // calculate k3 = h * f(x + h/2, y(x) + k2/2)
		  for (int i = 0; i < 2; i++) {
		    yStartk3[i] = yStart[i] + k2[i] / 2.0f;
		  }
		  dydxk3 = dydx(xStart + h/2.0f, yStartk3, dydxk3);
		  for (int i = 0; i < 2; i++) {
		    k3[i] = h * dydxk3[i];
		  }

		  // calculate k4 = h * f(x + h, y(x) + k3
		  for (int i = 0; i < 2; i++) {
		    yStartk4[i] = yStart[i] + k3[i];
		  }
		  dydxk4 = dydx(xStart + h, yStartk4, dydxk4);
		  for (int i = 0; i < 2; i++) {
		    k4[i] = h * dydxk4[i];
		  }

		  // calculate y(x + h)
		  for (int i = 0; i < 2; i++) {
		    yEnd[i] = yStart[i] + k1[i] / 6.0f + k2[i] / 3.0f + k3[i] / 3.0f + k4[i] / 6.0f;
		  }

		
		return yEnd; 	
	}
	
	public float[] dydx(float x, float y[], float dydx[]){
	  // y[0] is position
	  // y[1] is velocity, dy[0]/dx

	  // d/dx(dy[0]/dx) = acceleration = - y[0]
	  float acceleration = -1.0f * y[0];

	  dydx[0] = y[1];
	  dydx[1] = acceleration;
	  
	  return dydx;
	}

	
	// Retrieve the value of an applet parameter
	public String getParameter(String key, String def) {
		return isStandalone ? System.getProperty(key, def) :
			(getParameter(key) != null ? getParameter(key) : def);
	}

	// Get info on the applet parameters
	public String[][] getParameterInfo() {
		return null;
	}

	// Get applet information
	public String getAppletInfo() {
		return "Applet Information";
	}

	// Initialize the applet
	public void init() {
		try {
			initComponents();
		}
		catch (Exception e) {
			e.printStackTrace();
		}
		// double buffering
		size   = this.size();
		buffer = this.createImage(size.width, size.height);
		bufferGraphics = buffer.getGraphics();
		please_stop = false;
		
		yStart = new float[2];
  		yStart[0] = 1;
  		yStart[1] = 0;
  		dt = 0.01f;
		t = 0;
		stopt = (float)(100.0f*Math.PI);
		colCount = 0;
		last_x=100;
		last_y=300;
		clear = true;
	
		for(int i=0;i<100;i++) {
			col[i] = new Color((float)Math.random(),(float)Math.random(),(float)Math.random());
		}
	
  		//yEnd = new float[2];
  		
  		
  		this.addMouseListener(new MouseAdapter() 
			{
				public void mouseClicked(MouseEvent e) 
					{	
						
						last_mx = e.getX();
						last_my = e.getY();
						if ((last_mx>400)&&(last_mx<410)&&(last_my>300)&&(last_my<310)) {
							clear = true;
						}
					}
				});
				
		// event model 1.1 mouse listener
		this.addMouseMotionListener(new MouseMotionAdapter() 
		  {
			  public void mouseMoved(MouseEvent e) 
				 {
				     int x = e.getX(), y = e.getY();
				     
				     if ((x>100)&&(x<200)&&(y>300)&&(y<310)){
				     	//last_x = Math.min(x,800);
				     	//last_y = Math.min(y,600);
				     	dt = (x-99)/100.0f;
				     	last_x = x;
				     	last_y = y;
				     }
				     
				   }
			 });	
  		
				
	}

	public void initComponents() throws Exception {
// IMPORTANT: Source code between BEGIN/END comment pair will be regenerated
// every time the form is saved. All manual changes will be overwritten.
// BEGIN GENERATED CODE
		// the following code sets the frame's initial state
		setLocation(new java.awt.Point(0, 0));
		setLayout(null);


		setSize(new java.awt.Dimension(800, 400));

		// event handling

// END GENERATED CODE
	}
	
	
	public void paint(Graphics screen) {
		if (clear) {
        	bufferGraphics.setColor(Color.white);
        	bufferGraphics.fillRect(0, 0, size.width, size.height); // clear the buffer
        	clear = false; 
        }
        bufferGraphics.setColor(col[colCount]);
        
        bufferGraphics.drawRect((int)(t*2.0f)+30,(int)(yEnd[0]*100.0f)+150,1,1);
        
        
        bufferGraphics.setColor(Color.white);
        bufferGraphics.fillRect(30,270, 400, 50);
        bufferGraphics.setColor(Color.black);
        
        
        bufferGraphics.drawLine(30,150,658,150);
        bufferGraphics.drawRect(30,50,628,200);
        bufferGraphics.drawString(" 0.0",5,150);
        bufferGraphics.drawString(" 0.5",5,100);
        bufferGraphics.drawString("-0.5",5,200);
        bufferGraphics.drawString(" 1.0",5,50);
        bufferGraphics.drawString("-1.0",5,250);
        
        bufferGraphics.drawRect(400,300,10,10);
        bufferGraphics.drawString(" clear screen", 410,310);
        
        bufferGraphics.drawRect(100,300,100,10);
        bufferGraphics.fillRect(last_x-1,300,2,10);
        bufferGraphics.drawString("Stepsize: " + String.valueOf(dt),last_x-1,295);
        
        //draw screenbuffer
        screen.drawImage(buffer, 0, 0, this);
   	}
	
	
	
	 // this one is for updating during runtime	
    Graphics screeng;
    public void update() {
        if (screeng == null) screeng = this.getGraphics();
              paint(screeng);
    }
	public void run() {
        while(!please_stop)
        {
			while (true){
					if (t> stopt)
					{
						yStart[0] = 1;
  						yStart[1] = 0;
  						dt = 0.01f;
  						last_x =(int)((dt*100.0f)+100);
						t = 0;
						if (colCount>100) {colCount=0;}
						colCount += 1;
						clear = false;
                    }
                    yEnd = calculate(dt, t, yStart, yEnd);
			 		
			 		for (int i = 0; i < 2; i++) {
      					yStart[i] = yEnd[i];
    				}

			 		t += dt;
			 		//yEnd[0] = (float)Math.sin(t);	
                    update(); 
                }
	 	}
        animator = null;
    }

	public void start() {
        if (animator == null) {
              please_stop = false;
              animator = new Thread(this);
              animator.start();
        }
    }

    // Standard method to stop the applet
    public void stop() 
	{
		please_stop = true;
	}
	// Standard method to destroy the applet
	public void destroy() {
	}

	// Main entry point when running standalone
	public static void main(String[] args) {
		rungekutta applet = new rungekutta();
		applet.isStandalone = true;
		Frame frame = new Frame();
		frame.addWindowListener(new java.awt.event.WindowAdapter() {
			public void windowClosing(java.awt.event.WindowEvent e) {
				Frame f = (Frame) e.getSource();
				f.setVisible(false);
				f.dispose();
				System.exit(0);
			}
		});
		frame.setTitle("Applet Frame");
		frame.add( applet, BorderLayout.CENTER );
		applet.init();
		applet.start();
		frame.setSize( 400, 320 );
		Dimension d = Toolkit.getDefaultToolkit().getScreenSize();
		frame.setLocation( (d.width - frame.getSize().width) / 2,
			(d.height - frame.getSize().height) / 2);
		frame.setVisible( true );
	}

}