Grid.java

import javafx.scene.Group;
import javafx.scene.*;
import javafx.scene.paint.*;
import javafx.scene.shape.*;
import javafx.collections.*;



public class Grid {

    public static void draw(Group grp) {

	double res = grp.getScaleX();
	Color c = Color.rgb(220,200,255);

	// shape 1 in Grid
	Rectangle r = new Rectangle(-4.0,-4.0,8.0,8.0);
	r.setFill(Color.TRANSPARENT);
	r.setStroke(Color.BLACK);
	r.setStrokeWidth(1/res);


	// grid lines (shape 2)
	double u = 4.0;
	Path p1 = new Path();
	ObservableList<PathElement> p = p1.getElements();
	for (int i=-4; i<=4; i++) {
		double v = i;
		p.add(new MoveTo(-u,v));
		p.add(new LineTo(u,v));
		p.add(new MoveTo(v,-u));
		p.add(new LineTo(v,u));
	}
	p1.setStrokeWidth(1.0/res);
	p1.setStroke(c);

	// locate origin (shape 3)

	Path p2 = new Path();
	p = p2.getElements();	
	u = 0.05;
	p.add(new MoveTo(-u,u));
	p.add(new LineTo(u,-u));
	p.add(new MoveTo(-u,-u));
	p.add(new LineTo(u,u));
	p2.setStrokeWidth(1.0/res);

	ObservableList<Node> ol = grp.getChildren();
	ol.addAll(r,p1,p2);
   }
	
}