// Stage.java-- illustrates the stage lighting example of the book

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

public class Stage extends Applet  {
	TextField x_text, y_text, r_text;
	Label     x_label, y_label, r_label;
	Button	draw_button;
	Graphics my_graphics;

	// These determine the origin in Graphics coordinates
	int origin_x = 125;
	int origin_y = 60;
	
	// setup the gui
	public void init ()  {
		x_text = new TextField("0", 3);
		y_text = new TextField("0", 3);
		r_text = new TextField("0", 3);
		
		x_label = new Label("x:");
		y_label = new Label("y:");
		r_label = new Label("r:");
		
		add(x_label);
		add(x_text);
		add(y_label);
		add(y_text);
		add(r_label);
		add(r_text);
		
		draw_button = new Button("Plot");
		add(draw_button);
		
		my_graphics = this.getGraphics();
	}
	
	// Draws a light on the stage_canvas with radius r
	// at x,y.
	void draw_light ( double x, double y, double r )  {
		// the Graphics.drawOval method draws an ellipse inside a rectangle,
		// but we are given a radius and center. The coords of the upper left
		// corner of the square bounding our circle is (x-r,y-r);
		
		int xcoord 	= (int)((x + origin_x) - r);
		int ycoord 	= (int)((origin_y - y) - r);
		int d	 	= (int)(2 * r);

		// Draw the circles in red
		Color old_color = my_graphics.getColor();
		my_graphics.setColor(Color.red);
		my_graphics.drawOval (xcoord, ycoord, d, d);
		my_graphics.setColor(old_color);
	}

	public boolean handleEvent ( Event e )  {
		if ( (e.target == draw_button) && e.id == Event.ACTION_EVENT )  {
		// try to convert the contents of the text fields
		// to numbers; if we succeed, draw the appropriate
		// stage light
		boolean number_ok = true;
		double x,y,r;

		try  {
			x = Double.valueOf(x_text.getText()).doubleValue();
		} catch (java.lang.NumberFormatException ex )  {
			number_ok = false;			
			x = y = r = 0.0;
		}
			
		try  {
			y = Double.valueOf(y_text.getText()).doubleValue();
		} catch (java.lang.NumberFormatException ex)  {
			number_ok = false;
			x = y = r = 0.0;
		}
		
		try  {
			r = Double.valueOf(r_text.getText()).doubleValue();
		} catch (java.lang.NumberFormatException ex)  {
			number_ok = false;			
			x = y = r = 0.0;
		}
					
			if ( number_ok ) 
				draw_light ( x,y,r );
		}

		return false;
	}
	

	// Draw cyan lines through the origin
	public void paint (Graphics g)  {
		Color old_color = g.getColor();
		Dimension d = size();
		
		g.setColor(Color.cyan);
		g.drawLine(origin_x,0, origin_x, d.height);
		g.drawLine(0,origin_y, d.width, origin_y);
		g.setColor(old_color);
	}
	
} // class Stage