import java.awt.*;
import java.lang.*;

public class Xraya extends java.applet.Applet {
	int MAXATOMS = 5;
	final int HRange=5,KRange=5;
	int x[] = new int[MAXATOMS+1];
	int y[] = new int[MAXATOMS+1];
	int current=1;
	final int nk=(2*HRange+1)*(2*KRange+1);
	double h[] = new double[nk+1];
	double k[] = new double[nk+1];
	double intensity[] = new double[nk+1];
	
	TextField xpos,ypos,message;

	public void init() {
	
		for (int n = 1;n<=MAXATOMS;n++) {
			x[n] = 0;
			y[n] = 0;
			}
		for (int f=1;f<=nk;f++) {
			h[f] = (f-1)/(2*HRange+1) - HRange;
			k[f] = (f-1)%(2*KRange+1) - KRange;
			intensity[f] = 0;
			}
	
		setLayout(new FlowLayout() );
		
		xpos = new TextField(String.valueOf(0),5);
		ypos = new TextField(String.valueOf(0),5);
		message = new TextField("",25);

		add(new Label("x:"));
		add(xpos);
		add(new Label("y:"));
		add(ypos);
		add(message);
		add(new Button("Xray"));
		add(new Button("Restart"));
		}//End init
	
	void restart(){
		current = 1;
		for (int n = 1;n<=MAXATOMS;n++) {
			x[n] = 0;
			y[n] = 0;
			}
		for (int f=1;f<=nk;f++) {
			intensity[f] = 0;
			}
		repaint();
		}

	public boolean action(Event e, Object arg) {
		if (e.target instanceof Button) {
			String command = (String)arg;
			if (command.equals("Xray")) {
				diffract();
				}
			if (command.equals("Restart")) {
				restart();
				}
			repaint();
			}
		return true;
		}//End action

	public boolean mouseDown (Event e, int xin, int yin) {
		if (current<=MAXATOMS) {
			if (xin>=10&&xin<=450&&yin>=50&&yin<=350) {
				x[current] = -10+xin;
				xpos.setText(String.valueOf(x[current]));
				y[current] = 350-yin;
				ypos.setText(String.valueOf(y[current]));
				current++;
				message.setText("");
				}
			else {
				message.setText("Click on the blue area");
				}
			}
		else {
			message.setText("Five spots have been entered");
			}
		repaint();
		return true;
		}//End mouseDown
		
	void diffract() {
		double im,re,arg;
		double xmid[] = new double[nk+1];
		double ymid[] = new double[nk+1];
	  	int n,f;

		for(n=1;n<=MAXATOMS;n++) {
			xmid[n] = (double)(x[n])/450;
			ymid[n] = (double)(y[n])/300;
			}
		for(f=1;f<=nk;f++) {
			re = im = 0;
			for(n=1;n<=MAXATOMS;n++) {			
				arg = (double)( 2*3.14159*( h[f]*xmid[n]+k[f]*ymid[n] ) );
				re += (double)(Math.cos(arg));
				im += (double)(Math.sin(arg)); 
				}
			intensity[f] = re*re+im*im;
			}
		}//End diffract

	public void paint(Graphics g) {
		int xdraw,ydraw;
		int kxdraw[] = new int[nk+1];
		int kydraw[] = new int[nk+1];

		//Set up Atomic box and Frequency domain
		g.setColor(Color.blue);
		g.fillRect(10,50,450,300);
		g.setColor(Color.cyan);
		g.fillRect(10,400,450,50);
		
		//Add coordinate axes
		g.setColor(Color.black);
		g.drawLine(10,50,10,350);
		g.drawLine(10,350,460,350);
		g.drawLine(10,400,10,450);
		g.drawLine(10,450,460,450);
	
		//Add atoms to the field
		g.setColor(Color.red);
		for (int n=1;n<=MAXATOMS;n++) {
			if(x[n]!=0&&y[n]!=0) {
				xdraw = 10+x[n];
				ydraw = 350-y[n];
				g.fillOval(xdraw-5,ydraw-5,10,10);
				}	
			}
	
		//Add the frequency components
		for (int f=1;f<=nk;f++) {	
			kxdraw[f] = (int)(10+3.75*f);
			kydraw[f] = (int)((450-2.5*intensity[f]));
			}
		for (int f=1;f<=nk-1;f++) {
			g.drawLine(kxdraw[f],kydraw[f],kxdraw[f+1],kydraw[f+1]);
			}
		}//End paint
	}