Game Boards - Reversi

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Problem Description

TPanels Reversi

TShapes Reversi

TStringGrid  Reversi

Here is an exercise in game board design.  Three 8x8 boards are built along with the logic to move pieces in response to user clicks.   In this case,  I chose the game of "Reversi" (aka Othello®) to implement for each board.  The boards are:

bulletan array of TPanel controls,
bulletan array of TShape controls, and
bulleta single TStringGrid control with 8 columns and 8 rows of cells. 

Background & Techniques

A young Delphi student (from a foreign country of course  -  I think we have no such thing in the USA), recently wrote asking for help in designing a board for a class assignment.  She had carefully  hand placed 64 TPanels on the form and created 64 OnClick event exits, but didn't quite know how to proceed from there.   I didn't either.  I  suggested to her that it would be better to dynamically create an array of TPanels and use subscripting to access them.   That led me to wonder about the trade offs  using 64 TPanel controls vs. my normal approach - a single TStringGrid.        Only one way to find out - try them both.  Since the panels were restricted to square shapes, I also created an array of circular TShapes.

Reversi Rulesi

To make the boards comparison realistic we need to do something with them.   I chose the game of Reversi because the rules are simple and it looked quite easy to implement.  Each player starts with two tiles of their color arranged diagonally on the center squares as in the first board in the images above.  I chose Red and Blue as the piece colors and player names.  In this version Red always plays first.    For each turn, player X must click on an empty square that completes  a line of one or more consecutive opponent pieces with a player X piece on each end.   The line can be extend in any of 8 directions from the clicked square, (left, right, up down, and the 4 diagonals).  When clicked, all opponent's pieces in each such line from the the clicked square are "reversed" to become player X pieces.  Play continues alternating turns until all squares are filled.  The player with the most pieces wins.   If a situation occurs where a player has no valid move, he passes that turn an the opponent plays again.  

While the program is mainly intended to illustrate game board building techniques, they are all playable - in fact three games can be played simultaneously, one on each board.   Message labels above each board give turn information and current score,  A second message line reports cases with no move available and game winner information.

Non-programmers are welcome to read on, but may want to skip to the bottom of this page to download executable version of the program.

Creating the boards

Global variables Offsetx, OffsetY and Panelsize define the location and cell size for each board.  Board2 and Board3 start at 9 and 18 panel size increments to the right of Board1.  The FormActivate method creates all of the components for the boards.  Beginners frequently have problems creating visual controls because the Parent property must be specifically assigned.   Parent is the windowed control that will control the drawing and redrawing of the child controls.  For Board1, the TPanel board, the parent is "self", the main form.  For Board2, the TShapes, I created a Tpanel to frame them and assigned it as the parent for each shape control.  Board3 is single TStringControl with 8 columns and 8 rows.

Click handling

TPanels can respond to clicks via an OnClick event exit,  so that's the logical place to process user clicks on board pieces.  To build the exit, it's easiest to drop a TPanel on the form temporarily, create an OnClick exit, delete the panel and use the blank exit as the model for our click handling code.  How to keep track of which pieces are where on the board?  For the  simplest case, we can use the Tag property to indicate the cell status.  Tag is a "spare"  integer field defined for every Delphi control.  We'll use Tag values of 0 for empty, 1 for a Red piece and 2 for a Blue piece.    If more complicated entries were required  (for example, if pieces had multiple properties like color and type and  value and power and smell or whatever, we could make our own class  descended from TPanel  [TPiece=class(TPanel)] and extend it with the additional properties we needed.  But not in this case.   Local function ValidMove returns true if the clicked empty cell adjoins at least one string one or more opponents pieces between it and another piece of the clicker's color.   If ValidMove returns true, procedure MakeMoves actually changes the Tag values of the cells to indicate change all of the adjoining strings of opponent's pieces to my pieces plus adding a piece of my color on the the clicked cell.  This change is applied in all 8 directions. 

For the 2nd board, we'll use TShapes to make circular cells.  TShapes are descendents of TGraphicControl, a visual control type that has less overhead than the standard windows TWinControl.  TPanels descend  from TWinControls.   Unlike TPanels, TShapes do not have an OnClick event exit available.   It is only a minor inconvenience though to use the OnMouseUp event exit instead.     In this 2nd try at handling clicks, I combined the ValidMove function with the MakeMoves procedure.  The MakeMoves function now returns the total score for the pieces added and has a "Moveit" parameter that determines whether or not the move is actually made.   

Finally, the 3rd board is a TStringGrid.  Now we have only one control (and  thus only one Tag value, but we can use the 64 cell values to indicate who occupies each cell.  An OnSelect event exit is called with each clicked cell with column and row passed as parameters.  The same MakeMoves logic used in Board2 is applied here.   An OnDrawCell exit  checks the value to determine what piece (colored circle)  to draw each time the board need redrawing.   

Comparing the types, String grids would make it easier to show a cell and the piece on the cell as separate entities, for example if we wanted a black and white checkerboard pattern for the board.   Dragging pieces or animating piece movement seems like it would be possible under any of the  boards - guess we'll need another version of the program to check that out.  In the meantime, perhaps someone will find this useful.


.Running/Exploring the Program 

bulletBrowse Source Extract
bulletDownload source
bulletDownload  executable

Suggestions for Further Explorations

Convert one of the boards to a documented Reversi game with computer as an  opponent option..
Make a version that incorporates piece dragging for user moves and animation for computer moves.  


Original Date: November 30, 2004 

Modified: May 15, 2018

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