/*
    Faraday induction applet
 */

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

public class faraday extends Applet {
    public MediaTracker tracker;
	public Image offScreenImage;
	public Image theBox;
	public boolean copyRight = false;

	public boolean dragLoop = false, pole = false;
	public int loop = 100, loop1, v=0, v1=0, vmax=50, dx = 0;
	public int ytop = 234 - 20;
	public int ybot = 234 + 20;

	public void init() {
		super.init();		
		// load the backgrond image
		tracker= new MediaTracker(this);
		theBox = this.getImage(getCodeBase(),"magnet.jpg");
		tracker.addImage(theBox,0);
		try {
	    	tracker.waitForID(0);
		} catch (InterruptedException e) {
		}
		offScreenImage = createImage(500,350);

		//{{INIT_CONTROLS
		setLayout(null);
		resize(500,350);
		//}}
	}

	public void update(Graphics g){
		Graphics offg = offScreenImage.getGraphics();
		paint(offg);
		g.drawImage(offScreenImage, 0, 0, this);
	}

	public void paint(Graphics g){
		g.setColor(Color.white);
		g.fillRect(0,0,500,350);
		g.drawImage(theBox,0,0,theBox.getWidth(this),theBox.getHeight(this),this);
		
		// galvanometer needle
		g.setColor(Color.blue);
		int x = 78 + v;
		if (pole) x = 78 - v;
		int y = 105 - (int)(Math.sqrt(73*73 - v*v));
		g.drawLine(78,105,x,y);
		g.fillOval(x-3,y-3,7,7);
		
		// loop
		int xlt = loop - 35 - 26;
		int xlb = loop - 35 + 26;
		int xrt = loop + 35 - 26;
		int xrb = loop + 35 + 26;
		int xt1 = loop +  7 + 26;
		int xt2 = loop -  7 + 26;
		g.setColor(Color.red);
		for (int i=-1; i<=1; i++) {
			g.drawLine(xlt-i,ytop+i,xrt-i,ytop+i);
			g.drawLine(xrt-i,ytop+i,xrb-i,ybot+1);
			g.drawLine(xrb-i,ybot+i,xt1-i,ybot+i);
			g.drawLine(xlb-i,ybot+i,xt2-i,ybot+i);
			g.drawLine(xlb-i,ybot+i,xlt-i,ytop+i);
		}
		// matching cable endpoints
		g.setColor(Color.green);
		g.fillOval(xt1-4,ybot-4,8,8);
		g.fillOval(59,137,8,8);
		g.setColor(Color.yellow);
		g.fillOval(xt2-4,ybot-4,8,8);
		g.fillOval(87,139,8,8);
		
		// write polarity on magnet
		g.setColor(Color.green);
		g.setFont(new Font("Helvetica", Font.BOLD, 24));
		if (pole) {
			g.drawString("+",188,175);
			g.drawString("-",188,317);
		} else {
			g.drawString("-",188,175);
			g.drawString("+",188,317);
		}
			
		// copyright notice:
		if (copyRight) {
			g.setColor(Color.green);
			g.fillRect(100,100,240,70);
			g.setColor(Color.white);
			g.setFont(new Font("Helvetica", Font.PLAIN, 18));
			g.drawString("This applet was written by:",110,120);
			g.drawString("Wolfgang Bauer",110,140);
			g.drawString("Copyright: WB 1999",110,160);
		}
	}

	public boolean handleEvent(Event event) {
		int xclick = event.x;
		int yclick = event.y;
		if (event.target == this && event.id == Event.MOUSE_DOWN) {
			dragLoop = false;
			System.out.println("x:"+event.x+"; y:"+event.y);
			if (yclick<ybot && yclick>ytop && xclick<loop+40 && xclick>loop-40) {
				dx = loop - xclick;
				loop1 = loop;
				dragLoop = true;
			}
			if (yclick<203 && yclick>122 && xclick<209 && xclick>182) {
				pole = !pole;
				repaint();
				return true;
			}
			if (yclick<348 && yclick>265 && xclick<209 && xclick>182) {
				pole = !pole;
				repaint();
				return true;
			}
		}
		if (event.target == this && event.id == Event.MOUSE_DRAG) {
			if (dragLoop) {
				loop = xclick  + dx;
				if (loop > 154 && loop < 234) {
					v = 8*(loop - loop1);
					v = (v+v1)/2;  // this just damps the galv. motion
					if (v > vmax) v = vmax;
					if (v < -vmax) v = -vmax;
					v1 = v;
				} else {
					v = 0;
				}
				loop1 = loop;
				repaint();
				return true;
			}
		}
		if (event.target == this && event.id == Event.MOUSE_UP) {
			dragLoop = false;
			v = 0;
			v1 = 0;
			repaint();
			return true;
		}
		return super.handleEvent(event);
	}

	//{{DECLARE_CONTROLS
	//}}
}