// Applet to display single slit diffraction
// Gary D. Westfall
// January, 1998
import java.awt.*;
import java.applet.Applet;

public class diffrac extends Applet {
	Image offscreenImage;
	String imageName="spectrum.jpg";
    public MediaTracker tracker;
	public Image image;
	public void init() {
		setBackground(Color.white);
		
		tracker= new MediaTracker(this);
		image=this.getImage(getDocumentBase(),imageName);
		tracker.addImage(image,0);
		try {
	    	tracker.waitForID(0);
		} catch (InterruptedException e) {
		}
		setupMyImage();
		centerCanvas c = new centerCanvas(image,offscreenImage);
		Panel westPanel;
		westPanel = new WestPanel(c);
		
		setLayout(new BorderLayout());
		add("West",westPanel);
		add("Center",c);
	}

	public void setupMyImage() {
		if (offscreenImage != null) {
			offscreenImage.flush();
		}
		offscreenImage=createImage(500,300);
	}
}

class centerCanvas extends Canvas {
	boolean myReset;
	double a=10.0;
	double lambda=550;
	Image myOffImage,spectrumImage;
	Graphics offg;
	
	public centerCanvas(Image i1,Image offImage) {
		spectrumImage=i1;
		myOffImage=offImage;
		offg = offImage.getGraphics();
		repaint();
	}
	
	public void update(Graphics g) {
		paint(g);
	}
	
	public void paint(Graphics g) { 
		drawMyBackground(g);
	}
	
	public void drawMyBackground(Graphics g) {
		int left=14;
		int right=350;
		int center;
		int i;
		double beta1,beta2,b1,b2;
		int x1,y1,x2,y2;
		int i1,i2;
		double factor;
		
		center = (right-left)/2 + left;
		offg.setColor(Color.white); // Clear background to white
		offg.fillRect(0,0,500,300);
		offg.setFont(new Font("TimesRoman",Font.BOLD,12));
		offg.setColor(Color.black); // Draw axes
		offg.drawImage(spectrumImage,74,5,this); // Put on light spectrum
		x1=74+(int)(((lambda-400.0)/300.0)*216.0);
		for(i=0;i<3;i++){
			offg.drawLine(x1+i-1,2,x1+i-1,27);
		}
		for(i=0;i<=2;i++){
			offg.drawLine(left,270+i,right,270+i);
			offg.drawLine(center+i-1,270,center+i-1,30);
		}
		for(i=1;i<9;i++){ // Draw ticks
			x1=i*20+center;
			x2=center-i*20;
			offg.drawLine(x1,265,x1,270);
			offg.drawLine(x2,265,x2,270);
		}
		for(i=1;i<5;i++){ // Axis labels
			x1=center+i*40-5;
			x2=center-i*40-7;
			i1=4*i;
			i2=-4*i;
			offg.drawString(""+i1,x1,285);
			offg.drawString(""+i2,x2,285);
		}
		x1=center-3;
		offg.drawString("0",x1,285);
		offg.drawString("Distance along screen (cm)",110,297); // x axis label;
		factor=2.0*Math.PI*(a*1.0e-6)/(2000.0*(lambda*1.0e-9));
		i1=left;
		x1=left-center;
		beta1=(double)(x1)*factor;
		b1=beta1/2.0;
		y1=(int)(240.0*(Math.sin(b1)/b1)*(Math.sin(b1)/b1));
		offg.setColor(Color.red);
		for(i=left+1;i<=right;i=i+2){
			x2=i-center;
			i2=i;
			beta2=(double)(x2)*factor;
			b2=beta2/2.0;
			y2=(int)(240.0*(Math.sin(b2)/b2)*(Math.sin(b2)/b2));
			offg.drawLine(i1,270-y1,i2,270-y2);
			x1=x2;
			y1=y2;
			i1=i2;
		}
		g.drawImage(myOffImage,0,0,this);
	}
	
	public void redraw(boolean reset) {
		repaint();
	}
	
	public void setvar(double aa,double lamlam) {
		a = aa;
		lambda = lamlam;
		repaint();
	}
}

class WestPanel extends Panel {
	Scrollbar abar;
	Scrollbar lambdabar;
	Label alabel;
	Label lambdalabel;
	Button reset;
	centerCanvas canvas;
	
	public WestPanel(centerCanvas c) {
		canvas=c;
		setBackground(Color.gray);
		setFont(new Font("TimesRoman",Font.PLAIN,12));
		setForeground(Color.white);
		setLayout(new GridLayout(0,1));
		
		add(new Label(""));
		add(new Label(""));
		add(new Label(""));
		add(new Label(""));
		
		add(new Label("Slit width (micrometers)",Label.CENTER));
		alabel = new Label("10",Label.CENTER);
		add(alabel);
		abar = new Scrollbar(Scrollbar.HORIZONTAL,1000,100,10,2500);
		add(abar);
		
		add(new Label(""));
		
		add(new Label("Wavelength (nanometers)",Label.CENTER));
		lambdalabel = new Label("550",Label.CENTER);
		add(lambdalabel);
		lambdabar = new Scrollbar(Scrollbar.HORIZONTAL,550,10,400,700);
		add(lambdabar);
		
		add(new Label(""));
		add(new Label(""));

		reset = new Button("Reset");
		reset.setForeground(Color.black);
		reset.setBackground(Color.lightGray);
		add(reset);
		
		add(new Label(""));
		add(new Label(""));
		add(new Label(""));
		add(new Label(""));
		add(new Label(""));
	}
	
	public boolean handleEvent(Event evt) {
		// Read the two scrollbars and set the two labels
		int anew,lambdanew;
		int lambdaint;
		double a,lambda;
		String label;
		
		if(evt.target instanceof Scrollbar) {
			anew = abar.getValue();
			lambdanew = lambdabar.getValue();
			
			a = (double)(anew)/100.0;
			lambda = (double)(lambdanew);
			lambdaint = (int)(lambda);
			
			canvas.setvar(a,lambda);
			
			alabel.setText(""+a);
			lambdalabel.setText(""+lambdaint);
			
			return true;
		} else if ((evt.id == Event.ACTION_EVENT) && (evt.target instanceof Button)) {
			label = ((Button) evt.target).getLabel();
			abar.setValue(1000);
			lambdabar.setValue(550);
			alabel.setText("10");
			lambdalabel.setText("550");
			a = 10.0;
			lambda=550.0;
			canvas.setvar(a,lambda);
			canvas.redraw(label.equals("Reset"));
			return true;
		}
		return false;
	}
	
}