/**
 *    Program:  Graph.html
 *    @author:  Paul Garrett, garrett@math.umn.edu
 *    @version: Sun Aug 15 19:34:16 CDT 1999
 *
 *    Purpose:  
 *
 */

//import lib.*;
import java.awt.*;

public class Graph extends java.applet.Applet {

	 TextField expressionField;
	 TextField valueOfXField;
	 Tree tree;
	 Button graphButton;

	 Panel p = new Panel();

	 boolean treeIsInitialized = false;

	 double xLeft = -3.0;
	 double xRight = 4.0 ;
	 final double inc = .05;
	 AxesAndGrid axg;

	 public void init() {
		  setLayout( null );
		  p.add(new Label("y ="));
		  expressionField = new TextField(40);
		  p.add(expressionField);
		  graphButton = new Button(" graph ");
		  p.add(graphButton);
		  p.resize(500, 35);
		  p.move(5, 385); 
		  add(p);

		  axg = new AxesAndGrid(10,10,500,400,xLeft,xRight);
		  double tot = (xRight - xLeft)*(4.0/5.0);
		  axg.setVerticalRange(-tot/3,2*tot/3);
	 }

	 public void paint(Graphics g) {
		  axg.draw(g);
		  if (treeIsInitialized == true) {
				g.setColor(Color.red);
				double y1, y2;
				for (double x=xLeft; x<=xRight; x+= inc) {
					 try {
						  y1 = tree.eval( x );
						  y2 = tree.eval( x+inc );
						  if ( Math.abs(y1) > 100 || Math.abs(y2) > 100 ) {
								throw new ArithmeticException();
						  }
						  axg.drawLine(g, x, y1, x+inc, y2);
					 }
					 catch( Exception e ) {
						  // just do nothing about it...
					 }
				}
		  }
	 }

	 public boolean action(Event e, Object ob) {
		  if (e.target == graphButton) {
				String str = expressionField.getText();
				XVector xv = MathParser.mathTokenize(str);
				try {
					 tree = MathParser.branchByParens( xv );
					 MathParser.branchByPrecedence( tree );
					 MathParser.finalizeLeaves( tree );
					 treeIsInitialized = true;
					 repaint();
					 return true;
				}
				catch (Exception ex) {
					 // do nothing
				}
		  }
		  return false;
	 }
    
}

/**************************************************
 *
 *   The End
 *
 ***************************************************/