// Applet to do kinetic theory simulation
// Gary D. Westfall
// August, 1997
import java.awt.*;
import java.applet.*;
import java.lang.*;
import java.util.*;


public class kinetic extends Applet
{
	Image offscreenImage;
	public void init() {
		
		setBackground(Color.white);

		setupMyImage();
		centerCanvas c = new centerCanvas(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 {
	int left=30;
	int right=385;
	int step=50;
	boolean myBegin,myReset;
	double volume=150.0;
	double oldvolume=150.0;
	double temp=200.0;
	double t=5.0;
	Rectangle r;
	Image myOffImage;
	Graphics offg;
	int numCollisions;
		
	public centerCanvas(Image offImage) {
		myOffImage=offImage;
		offg = offImage.getGraphics();
		myReset=true;
		repaint();
	}
	
	public void update(Graphics g){
		paint(g);
	}
	
	public void paint(Graphics g) {
		r = bounds();
		if(myReset){
			drawMyBackground(g);
			myReset=false;
		} else if (myBegin){
			drawMySim(g);
			myBegin=false;
		}
	}
	
	public void setvar(double voln,double tem,double tt){
		volume=voln;
		temp=tem;
		t=tt;
		if(volume != oldvolume){
			myReset=true;
			repaint();
			oldvolume=volume;
		}
	}
	
	public void redraw(boolean beginn,boolean reset){
		myBegin = beginn;
		myReset = reset;
		repaint();
	}
	
	public void drawMySim(Graphics g){
		double xx[] = new double[10];
		double yy[] = new double[10];
		double vx[] = new double[10];
		double vy[] = new double[10];
		int i,j,k;
		int x,y;
		double step;
		int diff;
		int w,h;
		int level;
		double v;
		double theta;
		int xspread,yspread;
		int numSteps;
		double ratio;
		long timeBegin,timeEnd,timeDiff;
		double xval,yval;
		
		offg.setFont(new Font("TimesRoman", Font.PLAIN, 12));
		w = r.width;
		h = r.height;
		level=h-(int)(volume);
		v=2.0*Math.sqrt(temp);
		xspread=w-18;
		yspread=h-level-14;
		numCollisions=0;
		for(i=0;i<10;i++){
			xx[i]=20.0+Math.random()*(double)(xspread-20);
			yy[i]=(double)(level)+15.0+Math.random()*(double)(yspread-20);
			theta=2.0*Math.PI*Math.random();
			vx[i]=v*Math.cos(theta);
			vy[i]=v*Math.sin(theta);
		}
		numSteps=10*(int)(t);
		step=0.1;
		timeBegin=System.currentTimeMillis();
		for(i=0;i<numSteps;i++){
			offg.setColor(Color.white);
			offg.fillRect(0,0,w,h);
			offg.setColor(Color.black);
			for(k=0;k<4;k++){
				offg.drawRect(k,k,w-2*k-1,h-2*k-1);
			}
			offg.setColor(Color.blue);
			offg.fillRect(4,h-(int)volume-50,w-8,50);
			offg.fillRect(w/2-20,4,40,h-(int)(volume)-10);
			offg.setColor(Color.red);
			for(j=0;j<10;j++){
				xval=xx[j]+(vx[j]*step);
				yval=yy[j]-(vy[j]*step);
				x=(int)xval;
				y=(int)yval;
				if(x > (r.width-9)){
					numCollisions++;
					diff = x - (r.width-9);
					x = x - diff;
					xval=(double)x;
					vx[j] = (-Math.abs(vx[j]));
				} else if (x < 9){
					numCollisions++;
					diff = 9 - x;
					x = x + diff;
					xval=(double)x;
					vx[j] = (+Math.abs(vx[j]));
				}
				if(y > (r.height-9)){
					numCollisions++;
					diff = y - (r.height-9);
					y = y - diff;
					yval=(double)y;
					vy[j] = (+Math.abs(vy[j]));
				} else if (y < (level+5)){
					numCollisions++;
					diff = (level+5) - y;
					y = y + diff;
					yval=(double)y;
					vy[j] = (-Math.abs(vy[j]));
				}
				xx[j]=xval;
				yy[j]=yval;
				offg.fillOval(x-5,y-5,10,10);
			}
			if(i == numSteps-1){
				offg.setColor(Color.white);
				offg.fillRect(6,h-45,150,38);
				offg.setColor(Color.black);
				offg.drawRect(6,h-45,150,38);
				offg.drawString("Number of collisions = "+numCollisions,10,h-30);
				ratio=(double)(numCollisions)/t;
				offg.drawString("Collisions.second = "+ratio,10,h-15);
			}
			g.drawImage(myOffImage,0,0,this);
			timeEnd=System.currentTimeMillis();
			timeDiff=timeEnd-timeBegin;
			if(timeDiff < 100){
					while (timeDiff < 100) {
						timeEnd=System.currentTimeMillis();
						timeDiff=timeEnd-timeBegin;
					}
			}
			timeBegin=timeEnd;
		}	
	}
	
	public void drawMyVGraph(Graphics g){
	}
	
	public void drawMyBackground(Graphics g){
		int w,h;
		int i;
		w = r.width;
		h = r.height;
		offg.setColor(Color.white);
		offg.fillRect(0,0,w,h);
		offg.setColor(Color.black);
		for(i=0;i<4;i++){
			offg.drawRect(i,i,w-2*i-1,h-2*i-1);
		}
		offg.setColor(Color.blue);
		offg.fillRect(4,h-(int)volume-50,w-8,50);
		offg.fillRect(w/2-20,4,40,h-(int)(volume)-10);
		g.drawImage(myOffImage,0,0,this);
	}
}

class WestPanel extends Panel
{
	Scrollbar volbar;
	Scrollbar tempbar;
	Scrollbar tbar;
	Label vollabel;
	Label templabel;
	Label tlabel;
	Button beginb;
	Button reset;
	centerCanvas canvas;
	Label numColLabel;
	Label rateLabel;
	
	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(""));
		vollabel = new Label("V = 150 cm^3",Label.CENTER);
		add(vollabel);
		volbar = new Scrollbar(Scrollbar.HORIZONTAL,150,10,50,246);
		add(volbar);
		add(new Label(""));
		templabel = new Label("T = 200 K",Label.CENTER);
		add(templabel);
		tempbar = new Scrollbar(Scrollbar.HORIZONTAL,200,20,0,400);
		add(tempbar);
		add(new Label(""));
		tlabel = new Label("t = 5 s",Label.CENTER);
		add(tlabel);
		tbar = new Scrollbar(Scrollbar.HORIZONTAL,5,5,5,60);
		add(tbar);
		add(new Label(""));
		setFont(new Font("TimesRoman", Font.PLAIN, 14));
		beginb = new Button("Begin");
		beginb.setForeground(Color.white);
		beginb.setBackground(Color.green);
		add(beginb);
		add(new Label(""));
		reset = new Button("Reset");
		reset.setForeground(Color.black);
		reset.setBackground(Color.lightGray);
		add(reset);
		add(new Label(""));
		add(new Label(""));
	}
	
	
	public boolean handleEvent(Event evt){
		// Read all three scollbars and set all three labels
		int volnew,tempnew,tnew;
		double vol,temp,t;
		String label;
		
		if(evt.target instanceof Scrollbar){
			volnew = volbar.getValue();
			tempnew = tempbar.getValue();
			tnew = tbar.getValue();
		
			vol = (double)(volnew);
			temp = (double)(tempnew);
			t = (double)(tnew);
		
			canvas.setvar(vol,temp,t);
		
			vollabel.setText("V = "+vol+" cm^3");
			templabel.setText("T = "+temp+" K");
			tlabel.setText("t = "+t+" s");
			return true;
		} else if ((evt.id == Event.ACTION_EVENT) && (evt.target instanceof Button)){
			label=((Button) evt.target).getLabel();
			canvas.redraw(	label.equals("Begin"),
							label.equals("Reset"));
			return true;
		}
		return false;
	}
		
}