// July 2002, java applet by Oliver Knill  for the CCP project
// Vector Fields and Line Integrals  by Oliver Knill and Dale Winter
// Harvard University, Nov 15, 2002. See
// http://www.math.duke.edu/education/ccp/materials/mvcalc/vfield/index.html
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License of the Free Software Foundation for
// details.  Compile with 
// javac pencil.java vectorfield.java lineintegral.java

import java.awt.*;

class pencil {

private int h,w;
private int x,y;                                // pencil location    
private int i,j;                                // indices
private int wr;                                 // wheel radius
private int wf;                                 // number vectors in each dimension
private int x_cen,y_cen;                        // pencil center
private int a,b;                                // new center
private int a_old,b_old;
private int x_old,y_old;
private int pencil_length=15;                   // pencil length

private int left_border=80;                     // left border for menu

public pencil(int width,int height) {
  this.w = width;   this.h = height;
  wf       = 4; 
  wr       = (int) w/70;                        
  x_cen    = w/2;        y_cen    = h/2;    
  x        = x_cen;      y        = y_cen;
  a        = x+pencil_length;  b  = y-pencil_length; 
}

public void read_pointer(int x, int y) { this.x = x+4; this.y = y-4; }

public void paint(Graphics g) {
    g.setColor(Color.black);
    g.fillRect(0,0,w,h);
}

private void erase_old_pencil(Graphics g) {
  g.setColor(Color.black         );           
  for (i=-1; i<2; i++)  for (j=-1;j<2; j++) {
    g.drawLine(x_old+i, y_old+j,a_old+2*i, b_old+2*j);
  }
  g.drawOval(x_old-wr, y_old-wr, 2*wr, 2*wr);
  g.fillOval(a_old-wf,b_old-wf,2*wf,2*wf-1);
  g.drawOval(a_old-wf,b_old-wf,2*wf,2*wf-1);
  g.drawLine(x_old-4,y_old+4,x_old,y_old); 
  g.drawLine(x_old-3,y_old+2,x_old,y_old+1); 
  g.drawLine(x_old-2,y_old+3,x_old+1,y_old); 
}

private void draw_new_pencil(Graphics g) {
  g.setColor(new Color(0,0,255));      
  for (i=-1; i<2; i++)  for (j=-1;j<2; j++) {
    g.drawLine(x+i, y+j, a+2*i, b+2*j);
  }
  g.setColor(new Color(0,0,127));
  g.fillOval(a-wf,b-wf,2*wf,2*wf-1);
  g.setColor(new Color(60,60,117));
  g.drawOval(a-wf,b-wf,2*wf,2*wf-1);
  g.setColor(new Color(200,200,255));
  g.drawLine(x-4,y+4,x,y); 
  g.drawLine(x-3,y+2,x,y+1); 
  g.drawLine(x-2,y+3,x+1,y); 
}

public void update( Graphics g ) {
  if (x_old>left_border) { erase_old_pencil(g); }
  a  = (int) (x+pencil_length);     b  = (int) (y-pencil_length); 
  if (x>left_border)     { draw_new_pencil(g);  } 
  a_old=a; b_old=b; x_old=x; y_old=y; 
}

}