/**
 * @Homework:  Assignment 6 (1 of 2)
 * @Exercise:  9.18 in textbook, page 534
 * @Author:    Richard Parry
 * @Version:   1.0 - August 3, 1998
 * @Filename:  GridLine.java
 * School:     UCSD, Summer 98 Java 1 class
 *
 * Description:
 * This applet displays a grid that is 8 x 8.  It can be easily
 * changed by modifying class constants.  The grid starting point
 * (upper left) is fixed. A button is provided which allows one to
 * change height and width of each cell resulting in the gird size
 * changing.  Random numbers are used for changing the cell
 * width and height. Each cell is created using the Graphics
 * class "drawLine" method. Note that the program does not draw
 * separate cells (4 individual line for each cell), but draws
 * lines and uses the intersection to create individual cells.
 * For example, an 8 x 8 grid is made by drawing 9 vertical and
 * 9 horizontal lines which results in 64 cells.
 **/

// import packages
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;



public class GridLine extends Applet implements ActionListener {

  // declare constants
  private final int X_START = 20;
  private final int Y_START = 40;
  private final int HORIZONTAL_CELLS = 8;
  private final int VERTICAL_CELLS   = 8;
  private Button makeGridButton;

  // declare instance variables
  private int cellWidth = 15;
  private int cellHeight = 20;
  private int xCellSize, yCellSize, horizontalLines, verticalLines;
  private int horizontalCells, verticalCells;
  private int i, xpos, ypos, xBegin, yBegin, xEnd, yEnd;


  /**
   * This is the initialization method called once which sets
   * various parameters.  It also configures the window with a
   * button that allows the user to modify the displayed grid.
   *
   * @param   - none
   * @return  - none
   **/
  public void init() {

    // initialize default values
    horizontalLines = VERTICAL_CELLS + 1;
    verticalLines   = HORIZONTAL_CELLS + 1;
    horizontalCells = HORIZONTAL_CELLS;
    verticalCells   = VERTICAL_CELLS;

    // initialize the button
    makeGridButton = new Button( "Make Grid" );
    makeGridButton.addActionListener( this );
    add( makeGridButton );

  } // end init method



  /**
   * This paint method displays the grid and the grid parameters
   * such as the number of cells, cell width and height, etc.
   *
   * @param  - Graphics object
   * @return -  none
   **/
  public void paint ( Graphics g ) {

    xpos = 250;
    ypos = 100;
    g.drawString ( "Horizontal Cells = " + horizontalCells, xpos, ypos );
    ypos += 15;
    g.drawString ( "Vertical Cells   = " + verticalCells, xpos, ypos );
    ypos += 15;
    g.drawString ( "Cell Width       = " + cellWidth, xpos, ypos );
    ypos += 15;
    g.drawString ( "Cell Height      = " + cellHeight, xpos, ypos );
    ypos += 15;

    // draw horizontal lines
    xBegin = X_START;
    yBegin = Y_START;
    xEnd   = X_START + horizontalCells * cellWidth;
    yEnd   = Y_START;
    for ( i = 0; i < horizontalLines; i++ ) {
      g.drawLine( xBegin, yBegin, xEnd, yEnd );
      yBegin = yBegin + cellHeight;
      yEnd   = yBegin;
    }

    // draw vertical lines
    xBegin = X_START;
    yBegin = Y_START;
    xEnd   = X_START;
    yEnd   = Y_START + verticalCells * cellHeight;
    for ( i = 0; i < verticalLines; i++ ) {
      g.drawLine( xBegin, yBegin, xEnd, yEnd );
      xBegin = xBegin + cellWidth;
      xEnd   = xBegin;
    }
  } // end paint method


  /**
   * This method is called each time the button is depressed
   * by the user. It changes the width and height of the
   * grid cells.
   *
   * @param   - action event from the mouse button
   * @return  - none
   **/
  public void actionPerformed( ActionEvent e ) {
    cellWidth  = 5 + (int) (Math.random() * 20);
    cellHeight = 5 + (int) (Math.random() * 20);
    repaint(); 
  } // end actionPerformed method


} // end class