How to program a chess: a forum based tutorial

llvllatrix · 2005-04-02T02:01:34

Introductions (ie what the heck is this thread about): This thread was born when da_grat1 asked me about model loading. After a bit of discussion it turned out that he was trying to program a chess game and wondered if I had any advice. The result; a good excuse to talk design. Although this may seem off topic on this forum, I think nehe is best for several reasons. This forum has a wide variety of visitors, both advanced and beginner (you'll see why this is important later...keep reading :) ). I also dont have to go over OGL, which we will be using to do our graphics. Most of you have also already taken a look at some general demo design as well as loading and playing sound, which is a bonus. Also note that da_grat1 will be trying to implement this, so I'm going to try my best to keep us on topic and drive us through the end. k, so its obvious that i cant tell you that if you follow steps 1 - X you'll successfully complete your project, or game ect. (lol, its just not possible) Instead, what I want to do with this thread is to start a discussion about game design from start to where ever we take it. Consider this an online, dynamic tutorial with many authors. You guys should feel free to tell me that I'm wrong (giving a reason for your decisions is very important because we are all of different expertise in different areas). Remember that even if you feel you cannot contribute because you dont have the experience, asking questions is just as valuable (they determine where this discussion will go). Questions you guys ask will determine what issues get addressed and in what order. So sit back and get ready for what will hopefully be a long and productive discussion. I think the best place to start is at the beginning. You'd be surprised how many people dont start there. Imagine how terrible it would be if you hired a company to build you a corporate headquarters for your multi-million dollar game development studio and when you open the door, the thing crashes down on you. Then, when your in your hospital bed you find out that its because the guys who built the place didnt do any planning or draw any blue prints and just started building the place without thinking twice. The reason this kind of thing doesn't happen with building companies is because architects and engineers design and test the building long before anyone uses a hammer or saw. However, this happens all to often in software engineering; people just dont start at the beginning. They jump into projects and start coding without design documents. Remember your friend who said he would make an amazing game and ended up not finishing it? Its because when he was nailing some code together, the structure fell straight down on top of his head and he couldnt continue...anyway I tink I made my point...design twice, build once...so lets get to some code design...that and I ran out of building analogies ;) ... Programming is like chewing a pack of bubble gum. If you chew it all at once you're going to die. Its best if you divide the pack into pieces and chew each separately. There’s no guarantee you're not going to choke on a small piece but at least if you do you can probably spit it back up. So the first thing to do is establish exactly what we hope to accomplish and then keep breaking it down till we can implement it. To break it down on a business level, the "what are we going to do" is the project proposal. The "break down" is the design document/feasibility study and the implement it is "code till it works". Side trackin': In this quick paragraph I'm going to describe my tendencies when it comes to game programming. Most of the reasons for this stuff comes from code on the cob (http://www.gamedev.net/reference/list.asp?categoryid=45#115) and we'll hopefully see it used and justified further on in the discussion. Game programming (unlike word processors) are made using synthesis. We are going to take elements like graphics, audio ect and put them together to make a product. To do the synthesis I typically use function libraries as the glue that holds my program together (think OpenGL's interface). Classes and inheritance usually dont work for this kind of thing (think MFC). I'm not saying to totally abandon classes, I'm saying "use them to do a job behind a function library so that whatever uses the library doesn’t have to know about them". Keep your interfaces clean and whatever you build with them will look ok...irregardless of what is behind the interface. What are we going to do? So we're making a chess game. It will have 3d pieces that move accross the board (as apposed to appearing where ever you clicked), an animated camera, ai which you can play against (not good ai, but ai none the less), a console for testing (not as complex as you think, but it will just take a long time to implement), sound for coolness, and the ability to save your game. That sound good to everyone? How are we going to do this? Well, first step is decomposition, but what exactly does that mean? If you refer to my side track up there, why are we decomposing, shouldn’t we be synthesizing? In truth, there are actually two different phases here that use different techniques to get their jobs done. The first phase is the design phase where we decompose our problem into sub problems till we are satisfied we can tackle them. Then we go to the implementation phase where we take the easiest sub problems, solve them, and their solutions to solve larger problems till we have a final solution; our game (this is what i mean by synthesis). So what is this design thingy all about? Decomposition is the answer to the question, "how the hell am i supposed to do that?" Design is about making a decomposition that works both now and in the future (you'll see what i mean). Pop quiz: what did a software blue print look like back when king tut was writing security software for his sarcophagus (namely the 7 Egyptian curses of death)? Ans: Same as they look today ; a pyramid. On the top of the pyramid is our goal (namely, a game) and on the very bottom is stuff we know we have to use to achieve our goal (our requirements). I our case, we have stuff like OpenGL, Windows, and fmod on the bottom. At the top of our pyramid is our chess game. Let the designing begin: A quick way to start is by listing a bunch of stuff you're probably going to need. In any game, we're going to need a main screen (the thing people see when they start the game), a game screen(the game itself), a menu (drawn over the screen), a way to tell if the game is over, a way to tell what screen gets input, a way to get the input, a way to keep track of time, a way to draw objects as apposed to triangles, a way to easily play a sound, a way to load files, a way for the ai to think, a way to control the camera, and a whole bunch of other stuff. The next thing to tackle is to organize this stuff in a pyramid and then fill in the gaps where we need to. We then keep doing this (decomposing these subsystems) till we can implement each subsystem without having to decompose it. So the next thing to tackle is to rearrange the subsystems i've listed (as well as others you guys come up with) into the pyramid and this i'm going to leave to anyone with time on their hands (this is a good exercise to do) or to my next post (which ever comes first). will post later, - llvllatrix

da_grat1

122

March 28, 2005 07:38 PM

ok... i will have a look at the code first... there might be a lot of questions I will ask.. just get ready... :)

O yeah.. I tried to play the game vs other player... I think there is something wrong with the rules.. It doesn't follow the rules.. lets say if i place my white pawn at the end of the black board position, lets say i capture the black castle there..usually we can change the pawn to queen, or etc.. but here it doesn't change.. it stuck there ..lol..

another thing is, when we check the king, it will straight away checkmate and the game end.. usually we can still move the king to other position to avoid the check right..

so this is the first question i will ask...
1. what kind of AI search algorithm does beowulf use? is it best first searh..emm I don;t think so.. is it A* algorithm ?

2. // Arrows + Home/End pad
#define UTIL_KEYBOARD_UP 273
#define UTIL_KEYBOARD_DOWN 274
#define UTIL_KEYBOARD_RIGHT 275

the above is how you define for the keyboard arrow key.. can you tell me how to define the alphabeth keys.. such as 'a' . 'b' etc... I think the value is different...such as the #define UTIL_KEYBOARD_UP the value is 273.. what about the alphabeth value key..

[Edited by - da_grat1 on March 29, 2005 1:38:14 AM]

llvllatrix

Author

340

March 29, 2005 06:50 AM

Hey,

My computer parts arrived yesterday, so I've been kinda busy :).

Quote:
1. what kind of AI search algorithm does beowulf use? is it best first searh..emm I don;t think so.. is it A* algorithm ?

I think its something like negamax. You can find a bunch of info on it at:
http://www.chessbrain.net/beowulf/theory.html

Quote:
2. // Arrows + Home/End pad
#define UTIL_KEYBOARD_UP 273
#define UTIL_KEYBOARD_DOWN 274
#define UTIL_KEYBOARD_RIGHT 275

the above is how you define for the keyboard arrow key.. can you tell me how to define the alphabeth keys.. such as 'a' . 'b' etc... I think the value is different...such as the #define UTIL_KEYBOARD_UP the value is 273.. what about the alphabeth value key..

Just use the ascii value. For example if you want the letter c you would pass 'c' to the function.

Keep up the good work,
- llvllatrix

da_grat1

122

March 29, 2005 04:30 PM

"game_res_draw_button_text(quit, left, right, bottom, top);"

can you explain to me about the "left,right,bottom,top"

"new_button.position(0.0f, 0.5f, 0.0f, 0.06f);"

and this new_button position.. the value of (0.0f, 0.5f, 0.0f, 0.06f).. how do you position it.. is it the same as x,y and z coordinate..

llvllatrix

Author

340

March 29, 2005 08:43 PM

Quote:
can you explain to me about the "left,right,bottom,top"

"new_button.position(0.0f, 0.5f, 0.0f, 0.06f);"

and this new_button position.. the value of (0.0f, 0.5f, 0.0f, 0.06f).. how do you position it.. is it the same as x,y and z coordinate..

There are two ways you can position a ui control and they are both handy for various things. The first and less frequently used is by using absolute coordinates. Basically the idea is that you are constantly updating the left, right, top, and bottom. For example, if you wanted to move the new button to the right then you would change the position to:

new_button.position(0.5f, 5.5f, 0.0f, 0.06f); // just add 5 to the right

This type of positioning is useful if you want to specify the absolute position of the control within a frame or something; the basic idea behind this type of positioning is that you really never want to change it (or at least change it often) because you could inadvertently end up stretching the control. Typically you set the position once and in most cases its easiest to just set it at the origin with the width and height values specified.

So how do we move the control if we're not going to constantly call position? Remember that our engine is completely based on opengl, so we can easily use the glTranslate functions to move anything before we draw it :). Keeping in mind that the origin is at the center, we can produce predictible ui and positioning values which are never distorted.

Using translation, we can position the button within a frame, and then translate the entire contents of the frame together. Translation also makes the code a lot easier to read. There is only one problem with translation; If we translate the controls, how does the mouse know where the control is? To solve this problem, I've written a set of mouse functions that translate the mouse using the inverse of the translation matrix. The end result; the mouse can easily be tested against any control irregardless of its positioning within opengl. The only tradeoff is that you have to "update" your buttons right after drawing them otherwise you will probably loose the gl translation.

Hope this helps,
- llvllatrix

da_grat1

122

March 30, 2005 08:25 AM

the game seems to have a lot of errors.. lol.. you only will be able to drag the pawn but not the other pieces such as knight.. etc... llvllatrix... can you fix that..
llvlltrix.. try to play the game.. try to play human vs human... once you play then you will discover a lot of bugs.. ;) The one I hate most is the game will end straight away when you check the second players' king while there are still many possible moves.. I think need to fix the beowulf engine.. Do you have time for that... :)

ohh yeah... another question

"glLoadName(8*z + x)" and "InitName"
what are those functions for?

[Edited by - da_grat1 on March 30, 2005 3:25:00 PM]

llvllatrix

Author

340

March 31, 2005 12:05 PM

Quote:
the game seems to have a lot of errors.. lol.. you only will be able to drag the pawn but not the other pieces such as knight.. etc... llvllatrix... can you fix that..
llvlltrix.. try to play the game.. try to play human vs human... once you play then you will discover a lot of bugs.. ;) The one I hate most is the game will end straight away when you check the second players' king while there are still many possible moves.. I think need to fix the beowulf engine.. Do you have time for that... :)

lol, yah; I was playing it the other day and noticed the same thing :) Things like that shouldnt be too hard to fix, so i'll leave it up to u guys.

Quote:
"glLoadName(8*z + x)" and "InitName"
what are those functions for?

These are functions used for "picking" or collision detection with the mouse to the individual pieces on the board. You can find out more about picking from:
http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=32

Unfortunately, I wont be able to do another game with you guys this month. I have to get ready for my next term at University, which starts two months from now. However, I should be able to get things rolling again in september. That said, here are a few of the things we will have to tackle:

Converting the tutorials into a manuscript for the book:
If everything goes according to plan, we should be able to convert our tutorial into a full fledged text book. This will consume most of my free time, but I think a lot of people will benefit. The text book will contain most of what has been presented here, along with more information on design and working on large projects. I will make sure to keep you guys up to date on what is going on with the book and of course I value your input. If theres an area you want to know more about, I'll do my best to accomodate you in the text.

Creating more new games with the engine:
So we have a pretty comprehensive engine and why not use it :) I would like to spend about the first month in september creating one small game (just one level) from the most common genres using the engine. The format will be same online tutorials. Naturally, we will be adding more to the engine as time goes by to accomodate our new games. So you guys have 5 months to come up with ideas for the games you want to tackle. These games will also end up in the text as well.

Cheers,
- llvllatrix

da_grat1

122

March 31, 2005 10:35 PM

alright....I'll wait till september for our new game.. :)
good luck for your exam..

da_grat1

122

April 02, 2005 02:01 AM

llvllrix....

everytime when i check the king it will be checkmate...just want to know whether the problem comes from the beowulf AI ENGINE... or you forgot to link it with the chess rules...
since you said it is simple :) can help to solve that problem? just the king problem.. because no fun.. everytime i play with my friend i will be the first one to lose the game... because he always check my king first.. due to that problem, we have to avoid from checking each others' king... :) because it will end the game..oo yeah.. there is no castling aswell :) maybe you can solve the problems in 20 minutes... really wish for that...

How to program a chess: a forum based tutorial

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How to program a chess: a forum based tutorial

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