import java.awt.*;
import java.lang.*;
import java.util.*;
import java.awt.event.*;

/**
  * Great Ideas in Computer Science: Chapter 6: Fractal
  *
  * @author   Ben Allen (bta@duke.edu)
  * 
  * This applet is the implementation of the fractal program discussed in Chapter 6.
  * The program was originally coded in pascal by D. J. Miller.  Some of the original
  * code has been translated and used in this applet. Comments have been included in these 
  * parts to give Miller credit.   
  * 
  */
  
public class fractal extends java.applet.Applet implements ActionListener
{
  double x,y,x0,y0,x1,y1,z,m,n,c1,c2;
  int i,j;
  int canvasXmax=200;              //Screen coordinates defined on following lines
  int canvasYmax=200;
  double xmax=200;      
  double ymax=200;
  double xmin=0;
  double ymin=0;
  Canvas graphArea;
  Button enterB;
  TextField c1Field,c2Field;
  
  /**
  * Applet initialized
  */
  public void init()
  {
    graphArea = new Canvas();
    graphArea.setSize(canvasXmax,canvasYmax);
    enterB = new Button("Enter");
    enterB.addActionListener(this);
    c1Field = new TextField(10);
    c2Field = new TextField(10);
    
    add(new Label("Constant1"));
    add(c1Field);
    add(new Label("Constant2"));
    add(c2Field);
    
    add(enterB);
    add(graphArea);
  }
  
  /**
  * Button handler method
  */
  public void actionPerformed(ActionEvent event)
  {
    Object cause = event.getSource();
    if (cause==enterB)
    {
      String tempString="";            //Temp variables used to input doubles from TextFields
      Double tempDouble;           
       
      tempString = c1Field.getText();  //Method of receiving doubles from TextFields
      tempDouble=new Double(tempString);
      c1 = tempDouble.doubleValue();
      
      tempString = c2Field.getText();
      tempDouble=new Double(tempString);
      c2 = tempDouble.doubleValue(); 
     
      drawFractal();
    }
  }
  
  /**
  * This procedure draws the fractal.  Originally coded in Turbo Pascal by Miller.  Slight
  * modifications have been made.
  */
  public void drawFractal()
  {
    Graphics g = graphArea.getGraphics();
    g.clearRect(0,0,canvasXmax,canvasYmax);
    g.setColor(Color.black);
    m=0;
    while (m<=200)
    { 
      x0=-2+(m/50);
      n=0;
      while (n<=100)                   //For each y on initial half
      {
        y0=2-(n/50);
        x=x0;
        y=y0;
        i=1;
        z=0;
        while ((i<=20) && (z<=4))      //check convergence
        {
          x1=(x*x) - (y*y) +c1;
          y1=(2*x*y) +c2;
          x=x1;
          y=y1;
          z=(x*x)+(y*y);
          i=i+1;
        }
        
        if (z<=4)                      //If convergence, plot
        {
          g.drawLine(screenX(m),screenY(n),screenX(m),screenY(n));
             //plot first half
          g.drawLine(screenX(200-m),screenY(200-n),screenX(200-m),screenY(200-n));
             //plot second half
        }
        n=n+1;
      }
      m=m+1;
    }
  }
  
  /**
  * Return x to be plotted to screen
  */
  int screenX(double realX)
  {
    return (int)realX;
  }
  
  /**
  * Return y to be plotted to screen
  */
  int screenY(double realY)
  {
    return (int)(canvasYmax-realY);
  }
   
}