// RectanglePanel.java
// From Cay Horstmann's Computing Concepts with Java 2 Essentials.
// Adapted by Scot Drysdale.  Further changes by THC.

// The RectanglePanel class is really our "canvas" for displaying the rectangle.

import java.awt.*;
import javax.swing.*;

public class RectanglePanel extends JPanel {  
  private static final long serialVersionUID = 1L;
  
  private Rect theRect;
  private static final int RECT_WIDTH = 20;
  private static final int RECT_HEIGHT = 30;

  // To construct a RectanglePanel, we also construct a Rect that it will display.
  public RectanglePanel() {  
    theRect = new Rect(0, 0, RECT_WIDTH, RECT_HEIGHT, Color.red);
    setBackground(Color.yellow);
  }

  // To draw on a JPanel, we DON'T call paint.  Instead, we call paintComponent.
  // paintComponent should ALWAYS have as its first line a call to
  // super.paintComponent.
  public void paintComponent(Graphics page) {  
    super.paintComponent(page); 
    theRect.fill(page);

    // Draw a grid.
    int panelWidth = getWidth();
    int panelHeight = getHeight();
    page.setColor(Color.lightGray);
    
    // Draw vertical grid lines.
    for (int x = 0; x < panelWidth; x += RECT_WIDTH)
      page.drawLine(x, 0, x, panelHeight);
      
    // Draw horizontal grid lines.
    for (int y = 0; y < panelHeight; y += RECT_HEIGHT)
      page.drawLine(0, y, panelWidth, y);
  }

  // Moves the rectangle.
  // The rectangle is moved by multiples of its full width or height.
  public void moveRectangle(int dx, int dy) {  
    theRect.move(dx * RECT_WIDTH, dy * RECT_HEIGHT);
  }
  
  // Draws the RectanglePanel.
  public void draw() {
    repaint();
  }
}