import java.awt.*;
import java.applet.*;
import java.lang.Math;
import java.awt.event.*;
import java.awt.AWTEvent.*;
import java.lang.Object;

public class NucScreen extends Applet implements AdjustmentListener
{
	private Image atomImage;			//for the atom.
	private Graphics g_atomImage;
	private double size, distance, electronDensity, radiusSq, k1;
	private double nuclearDensity, k2, k3; 
	private double highLightOffset, radiusHighLightOffsetSq, k4, k5;
	private double highLightDensity;
	private Scrollbar walker = new Scrollbar(Scrollbar.HORIZONTAL,0,10,0,110);
	private int walkerValue;
	private Panel controls = new Panel();
	private Label  left = new Label("  Far away");
	private Label right = new Label("  Very near");
	private int electronIntensity, nuclearIntensity, highLightIntensity;
	private int redComponent, greenComponent, blueComponent;
	private Label copyRight = new Label("Copyright 2006, Peter H. Bird");
	private Font def;
	
	public void init()  //Entry point for the applet.
	{
		walker.addAdjustmentListener(this);		//Listen to the scroll bar.
		setBackground(Color.white);
		atomImage = createImage(301,301);		//Off screen image of the atom.
		controls.setLayout(new BorderLayout());	//Controls below atom image.
		setLayout(new BorderLayout());
		g_atomImage = atomImage.getGraphics();
		controls.add("West",left);
		controls.add("North",walker);
		controls.add("East",right);
		add("South",controls);
		k1 = 0.0002;
		k2 = 0.1;
		k3 = 0.01;
		k4 = 0.5;
		highLightOffset = 0.5*Math.sqrt(k2);	//Nucleus highlight offset depends on nuclear size.
		makeAtomImage(g_atomImage);
		repaint();
	}
	
	public void paint(Graphics g)
	{
		Font def;
		g.drawImage(atomImage,0,15,null);		//Update the image of the atom
		def = g.getFont();
		Font f = new Font(def.getName(),Font.PLAIN,9);
		g.setFont(f);
		g.drawString("Copyright 2006, Peter H. Bird",10,10);
		g.setFont(def);
		walker.addAdjustmentListener(this);		// and turn the listener back on.
	}
	
	public void update(Graphics g)
	{
		paint(g);
	}
	
	public void adjustmentValueChanged(AdjustmentEvent evt)
	{
		walker.removeAdjustmentListener(this);			//Turn off listener for now.
		walkerValue = walker.getValue();				//Read slider value.
		k1 = 0.0002/(1.0 + 0.1*(float)(walkerValue));	//Will go from 0.0002 to 1.67E-5
		k2 = 10.0 + 0.818*(float)(walkerValue);			// will go from 10 to 100
		highLightOffset = 0.30*Math.sqrt(k2);
		k3 = 2.55*(float)(walkerValue);
		k4 = 0.3/(1.0 + 0.05*(float)(walkerValue));
		makeAtomImage(g_atomImage);
		repaint(0,0,301,316);
//		System.out.println("walker value = "+Integer.toString(walkerValue));
	}
	
	public void makeAtomImage(Graphics g_atom)
	{
		for (int i = 0; i <=300; i++)		//Main loops for offscreen image.
		{
			for (int j = 0; j <= 300; j++)
			{
				radiusSq = (i - 150)*(i - 150) + (j - 150)*(j - 150);	//Calculate radii.
				radiusHighLightOffsetSq = (i - 150 - highLightOffset)*(i - 150 - highLightOffset)
									+ (j - 150 + highLightOffset)*(j - 150 + highLightOffset);
				electronDensity = Math.exp(-k1*radiusSq);				//Calculate electron "density"
				electronIntensity = (int)(electronDensity*230.0);		// using a guassian distribution.
				if (radiusSq <= k2) nuclearDensity = Math.sqrt(k2 - radiusSq); else nuclearDensity = 0.0;
				nuclearIntensity = (int)(k3*nuclearDensity/10.0);		//Calculate nucleus using
				highLightDensity = Math.exp(-k4*radiusHighLightOffsetSq);// a spherical distribution.
				highLightIntensity = (int)(k3*highLightDensity/1.5);	//Calculate nuclear highlight
				redComponent = electronIntensity + highLightIntensity;	// using a gaussian distrib.
				if (redComponent > 255) redComponent = 255;				//Calculate RGB colour intensities.
				greenComponent = electronIntensity - nuclearIntensity + highLightIntensity;
				if (greenComponent > 255) greenComponent = 255;
				blueComponent = electronIntensity - nuclearIntensity + highLightIntensity;
				if (blueComponent > 255) blueComponent = 255;
				g_atom.setColor(new Color(redComponent, greenComponent, blueComponent));
				g_atom.drawLine(i,j,i+1,j);								//Set pixel.
			}
		}
	}
	
	public String getAppletInfo()
	{
		return "Name: NucScreen\r\n" +
		       "Author: Dr. P. Bird\r\n" +
		       "Created with Microsoft Visual J++ Version 1.0" +
			   "Copyright 2006";
	}
}