/* file la.java 
                   let user enter 2x2 matrix A.
                   show vectors for x and Ax when user clicks point x
*/

import java.applet.Applet;
import java.awt.*;
import java.util.*;
import java.awt.event.*;

class con extends Panel implements ActionListener, ItemListener
{
  la ap;
  Button   bt;
  CheckboxGroup cg;
  Checkbox cbvec,cbcir,cbbox;

  public con(la ap)
  { super();
    this.ap = ap;
    setBackground(new Color(192,96,0));
    cg = new CheckboxGroup();
    cbvec = new Checkbox("Vectors",true,cg);
    cbvec.addItemListener(this);
    cbcir = new Checkbox("Circles",false,cg);
    cbcir.addItemListener(this);
    cbbox = new Checkbox("Boxes",false,cg);
    cbbox.addItemListener(this);
    bt = new Button("Clear");
    bt.addActionListener(this);
    setLayout(new GridLayout(9,1));
    add(bt);
    add(cbvec);
    add(cbcir);
    add(cbbox);
    /*Canvas xicon = new Canvas();
    xicon.setBackground(ap.xcolor);
    Graphics xig = xicon.getGraphics();
    xig.drawRect(2,5,3,8);
    !!!xig.drawString("x",5,5);
    add(xicon);
    */
    //getGraphics().drawString("x color",10,60);
  }

  public void paint(Graphics g) // doesn't show up
  { g.setColor(ap.xcolor);
    g.drawString("x",5,80);
    g.setColor(ap.Axcolor);
    g.drawString("Ax",5,50);
    g.setColor(Color.black);
  }
  
  public void actionPerformed(ActionEvent e)
  { String s = (String)e.getActionCommand();
    if(s.equals("Clear"))
    { ap.graf.repaint();
      ap.txt.setText("");
      ap.setdefaults();
    }
  }

  public void itemStateChanged(ItemEvent e)
  {
    /* lots of trouble with this. 3 things that did not work:
       if(e.getSource() == cbvec)...
       if(e.getItem() == cbvec)...
       if(cbvec.getState() == true)...
    */
    if(cg.getSelectedCheckbox() == cbvec)
      ap.cbstate = ap.VEC;
    else if(cg.getSelectedCheckbox() == cbcir)
      ap.cbstate = ap.CIR;
    else
      ap.cbstate = ap.BOX;
  }
}

public class la extends java.applet.Applet
{ graph    graf;
  double   a,b,c,d,x1,x2,Ax1,Ax2;
  TextArea txt;
  con      ctrls;
  int      cbstate;
  static final int VEC = 0, CIR = 1, BOX = 2;         
  Color    xcolor,Axcolor;

  public void start(){}
  public void stop(){}
  public void init()
  { graf = new graph(this);
    txt = new TextArea("Welcome!\n",10,30);
    txt.setBackground(Color.white);
    xcolor = Color.orange;
    Axcolor = Color.blue;
    ctrls = new con(this);
    setLayout(new BorderLayout(3,3));
    add("West",ctrls);
    add("Center",graf);
    add("East",txt);
    a = 1.2; b = 0; c = 0; d = 0.5;
    cbstate = VEC;
    setdefaults();
  }

  public void setdefaults()
  { txt.append(" Click in the graph area.\n");
    txt.append("This defines a vector x.\n");
    txt.append(" If the 'Vectors' checkbox\n");
    txt.append("is selected,\n"); 
    txt.append("the applet will draw x in\n");
    txt.append("orange and Ax in blue,\n");
    txt.append("where A = [a  b]\n");
    txt.append("          [c  d]\n"); 
    txt.append(" If the 'Circles' checkbox\n");
    txt.append("is selected, we draw a\n");
    txt.append("the circle through x and \n"); 
    txt.append("show what A does to it. \n");
    txt.append(" If 'Boxes' is selected\n");
    txt.append("we draw a box through x and\n");
    txt.append("the origin and show how A\n");
    txt.append("transforms it.\n");
    txt.append(" Change a,b,c,d here too.\n\n");
    txt.append("a = "+Double.toString(a)+"\n");
    txt.append("b = "+Double.toString(b)+"\n");
    txt.append("c = "+Double.toString(c)+"\n");
    txt.append("d = "+Double.toString(d)+"\n\n");
  }


  public void parse()
  { StringTokenizer l = new StringTokenizer(txt.getText(),"\n;");
    while(l.hasMoreTokens())
    { if(!doline(l.nextToken()))
      { System.out.println(" Couldn't read elements. "); 
        return;
      }
    }
  }

  public boolean doline(String line)
  { // very crude parser reads the matrix entries a,b,c,d and 
    // ignores lines beginning with other characters
    char c1;
    int  fl = line.length(),
          j = 0;
    char form[] = line.toCharArray();
    while(( j < fl)&&Character.isSpaceChar(form[j]))
     j++;
    if( j == fl) 
      return true;
    String str;
    c1 = form[j];
    switch(c1)
    { case 'a': 
        while(((c1 = form[j]) != '=')&&( j < fl))
          ++j;
        str = String.valueOf(form,j+1,fl-j-1);
        a = Double.valueOf(str).doubleValue();
        break;

      case 'b':
        while(((c1 = form[j]) != '=')&&( j < fl))
          ++j;
        str = String.valueOf(form,j+1,fl-j-1);
        b = Double.valueOf(str).doubleValue();
        break;

      case 'c':
        while(((c1 = form[j]) != '=')&&( j < fl))
          ++j;
        str = String.valueOf(form,j+1,fl-j-1);
        c = Double.valueOf(str).doubleValue();
        break;

      case 'd':
        while(((c1 = form[j]) != '=')&&( j < fl))
          ++j;
        str = String.valueOf(form,j+1,fl-j-1);
        d = Double.valueOf(str).doubleValue();
        break;
     
      default:
        // ignore the comments in the txt
    }
    return true;
  }
}

class graph extends Canvas implements MouseListener
{ 
  private la    ap;
  int wd,ht,hafwd,hafht;

  public graph(la ap)
  { super();
    this.ap = ap;
    setBackground(new Color(128,64,0));
    setVisible(true);
    setSize(300,300);
    wd = getSize().width;
    ht = getSize().height;
    hafwd = (int)(wd/2);
    hafht = (int)(ht/2);
    addMouseListener(this);
  }

  public void paint(Graphics g)
  { g.clearRect(0,0,wd,ht);
    // draw x axis, y axis
    g.drawLine(0,hafht,wd,hafht); g.drawLine(hafwd,0,hafwd,ht);  
  }

  public void mousePressed(MouseEvent e){}
  public void mouseReleased(MouseEvent e){}
  public void mouseEntered(MouseEvent e){}
  public void mouseExited(MouseEvent e){}

  public void mouseClicked(MouseEvent e)
  {  ap.parse();
     if(ap.cbstate == ap.VEC)
       drawvectors(e);
     else if(ap.cbstate == ap.CIR)
       drawcircles(e);
     else
       drawboxes(e);
  }

  public void drawvectors(MouseEvent e)
  {  Graphics g = getGraphics();
     // use pixels as coordinates, and just translate origin
     // no rescaling is done
     double x1 = e.getX() - hafwd,
            x2 = hafht - e.getY(), // double_y = hafht - int_Y
           Ax1 = ap.a*x1+ap.b*x2, 
           Ax2 = ap.c*x1+ap.d*x2;
     // the origin is (hafwd,hafht).
     g.setColor(ap.xcolor);
     g.drawLine(hafwd,hafht,e.getX(),e.getY());
     g.setColor(ap.Axcolor);
     g.drawLine(hafwd,hafht,hafwd+(int)Ax1,hafht-(int)Ax2);
     g.setColor(Color.black);
     // write the coordinates into the text area
     ap.txt.append("x = ("+Double.toString(x1)
                      +","+Double.toString(x2)+")\n");
     ap.txt.append("Ax = ("+Double.toString(Ax1)
                       +","+Double.toString(Ax2)+")\n");
  }

  public void drawcircles(MouseEvent e)
  {  Graphics g = getGraphics();
     double  x1 = e.getX() - hafwd,
             x2 = hafht - e.getY(),
             r = Math.sqrt(x1*x1+x2*x2);
     g.setColor(ap.xcolor);
     g.drawOval(hafwd - (int)r,hafht - (int)r,2*(int)r,2*(int)r);
     g.setColor(ap.Axcolor);
     double x = r*Math.cos(0),
            y = r*Math.sin(0),
            Ax,Ay;
     int Pts = 25;
     for( int k = 1; k < 2*Pts+1; ++k)
     { double xnu = r*Math.cos(k*Math.PI/Pts),
              ynu = r*Math.sin(k*Math.PI/Pts);

       g.drawLine(hafwd+(int)(ap.a*x+ap.b*y),
                  hafht-(int)(ap.c*x+ap.d*y),
                  hafwd+(int)(ap.a*xnu+ap.b*ynu),
                  hafht-(int)(ap.c*xnu+ap.d*ynu));
       x = xnu;
       y = ynu;
     }
  }

  public void drawboxes(MouseEvent e)
  {  Graphics g = getGraphics();

     // double_y = hafht - int_Y
     g.setColor(ap.xcolor);
     int xlo = e.getX()-hafwd,
         ylo = hafht - e.getY(),
         xhi = 0, yhi = 0, t;
     if(xlo > xhi)
     { t = xhi; xhi = xlo; xlo = t;}
     if(ylo > yhi)
     { t = yhi; yhi = ylo; ylo = t;}
     g.drawRect(hafwd+xlo,hafht-yhi,xhi-xlo,yhi-ylo);

     g.setColor(ap.Axcolor);
     // draw image of segment from (xlo,ylo) to (xlo,yhi)
     double x1 = ap.a*xlo+ap.b*ylo, x2 = ap.a*xlo+ap.b*yhi,
            y1 = ap.c*xlo+ap.d*ylo, y2 = ap.c*xlo+ap.d*yhi;
     g.drawLine(hafwd+(int)x1,hafht-(int)y1,
                hafwd+(int)x2,hafht-(int)y2);
     // image of segment from  (xlo,ylo) to (xhi,ylo)
     x1 = ap.a*xlo+ap.b*ylo; x2 = ap.a*xhi+ap.b*ylo;
     y1 = ap.c*xlo+ap.d*ylo; y2 = ap.c*xhi+ap.d*ylo;
     g.drawLine(hafwd+(int)x1,hafht-(int)y1,
                hafwd+(int)x2,hafht-(int)y2);
     // image of segment from  (xhi,ylo) to (xhi,yhi)
     x1 = ap.a*xhi+ap.b*ylo; x2 = ap.a*xhi+ap.b*yhi;
     y1 = ap.c*xhi+ap.d*ylo; y2 = ap.c*xhi+ap.d*yhi;
     g.drawLine(hafwd+(int)x1,hafht-(int)y1,
                hafwd+(int)x2,hafht-(int)y2);
     // image of segment from  (xlo,yhi) to (xhi,yhi)
     x1 = ap.a*xlo+ap.b*yhi; x2 = ap.a*xhi+ap.b*yhi;
     y1 = ap.c*xlo+ap.d*yhi; y2 = ap.c*xhi+ap.d*yhi;
     g.drawLine(hafwd+(int)x1,hafht-(int)y1,
                hafwd+(int)x2,hafht-(int)y2);
  }
}

// end la.java