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Back to Hands-On Interactive Game Development

04.01 - Some Code to Ponder

Teej · 2002-03-28T07:34:38

Okay folks, no more fooling around…time to learn something. Have your compiler running with the BaseCode1 project loaded, and be sure that your DirectX 7.0 SDK documentation is easily accessible. If you’re missing some files, try here. The Rise and Fall of BaseCode1 Let’s turn our attention first to the overall layout of the program: Program execution starts at WinMain() (true for all Windows applications) The OS is instructed to create a full-screen window (black) Game_Initialize() is called DirectDraw is initialized DirectInput is initialized DirectSound is initialized The main message loop is entered (true for all Windows applications) Windows messages are handled in WindowProc() ESCAPE quits If there are no messages waiting, Game_Main() is called Check for input Clear the display Write a line of text Play a sound if the spacebar was hit Once the main message loop is exited (ESCAPE was hit), call Game_Terminate() DirectSound is shutdown DirectInput is shutdown DirectDraw is shutdown The program ends Or, more simply stated (ignoring Windows-related procedures): Game_Initialize() is called Game_Main() is called (repeatedly) Game_Terminate() is called It’s fairly common to see ‘entities’ such as our game code and the DirectX components asking for an opportunity to initialize before being used and a chance to take care of any shutdown tasks before they’re done. If our game requires memory for internal data, it would be a natural process to allocate the memory in Game_Initialize() which is called once at the beginning of the game, and free that memory in Game_Terminate() which is called before the game is completely terminated. Likewise, you’d expect that DirectX components don’t just work off-the-bat – we need to set them up first by calling their initialization functions and feeding them the correct information so that they work properly when they’re needed. Overall Layout The compiler doesn’t care if our template code is in one file or in fifty. It is only for readability that we ‘chop up’ the game’s functions into groups and assign them their own files. Face it – a game with 800 functions all in one file makes for messy game code. There will be an article discussing source files, header files and projects that will further explain the semantics to organizing code in files, so for now let’s just look at the contents of the files themselves: WinBase.cpp contains all of the code that is specific to Windows. We need to at least create a window and process messages coming in from the OS to be considered a true Windows program, and this file keeps them all in one place. It also contains the proper start of execution, WinMain() . Once we dissect this function, the entire flow of the program will make perfect sense. InitTerm.cpp contains, you’ve guessed it, all of the initialization and termination functions for our game template. Game_Initialize() calls other initialization functions, in a sense managing everything else in the game. In the same way, Game_Terminate() ensures that everything that would like a chance to shutdown gets called. This is our last chance to do things before our frame-by-frame code gets called repeatedly, so make sure everything’s prepared! GameMain.cpp is where all of the action takes place. This function is called repeatedly from the message loop in WinMain() , which means that whatever you put in this function is going to execute many times a second. It’s our job to make sure that the code is written to fit this style. If every call to Game_Main() produces a frame of animation on the display, we’ve got ourselves the chassis for a game. Utils.cpp is a convenient place to throw functions into that are used by other parts of the game. For instance, there are functions for loading bitmaps from disk in this file, which is used elsewhere. And there’s also a couple of header (.H) files: Utils.h contains a ‘description’, called a prototype or declaration, for each of the functions implemented in Utils.cpp. As long as any other source file has access to this header file, it can use the functions contained inside. Globals.h is the master header file for our game template code. Every source file needs to know about Globals.h in order to function properly. If we place any information inside of this header file, it is immediately accessible from anywhere in our entire game. Sounds like a good place for global variables, huh? That’s one of the primary purposes of this file. So, the rule of thumb is that every source file (.CPP) should include Globals.h so that we can use global variables properly, and any source file that needs to use a function from Utils.cpp should include Utils.h. As you can see at the top of each source file, including a header file is accomplished with the line #include “filename .h” , where filename is either Globals or Utils . Let’s look once more at our organizational ‘chart’ to really drive the point home: Create a window for our game: WinBase.cpp – WinMain() Initialize our game: InitTerm.cpp – Game_Initialize() Initialize DirectX components Draw animated frames: GameMain.cpp – Game_Main() Shutdown our game: InitTerm.cpp – Game_Terminate() Shutdown DirectX components End of game Divide and Conquer What we’re doing here is setting ourselves up to understand the game template code by attacking each component separately. Each of the following has initialization, runtime and shutdown duties: Our game code DirectDraw DirectInput DirectSound Since we don’t have a game yet, the template code just fills in each section with something simple to serve as a placeholder. For instance, we use DirectDraw to set up our display, but all we’re doing is writing a line of text. Heck, it even goes through the trouble of loading RESOURCE.BMP onto an internal buffer, but we don’t (yet) do anything with it. For input, we have the code necessary to read the keyboard, and all that this program is interested in is the spacebar. Using DirectSound, we load a single sound into memory and play it whenever the spacebar is pressed. Nothing too complicated for any of these components, but just enough to say that we used them – they’re initialized, used and terminated properly. Definitely something good to build on! Of the three DirectX components, only DirectDraw is truly essential. We don’t need fancy sounds this early in our studies, and even input isn’t absolutely necessary, but without DirectDraw we wouldn’t even be able to set our resolution, color depth or display anything on the screen. Therefore, it should come as no surprise that we’ll concentrate our attack there first, but not before looking at DirectX as a whole. Part of the beauty of using DirectX is that the components are used rather consistently – once you get the hang of using one component, the rest aren’t so difficult to manipulate. Questions? Comments? Please reply to this topic. Edited by - teej on April 23, 2001 5:45:57 PM

Hands-On Interactive Game Development Workshops

Started by Teej April 23, 2001 04:41 PM

41 comments, last by Teej 22 years, 5 months ago

Rictus

122

May 02, 2001 05:15 PM

Hi all, OK I''ve been through the code a hundred times and I don''t understand how it takes the bitmap and lets you type a message using the alaphabet from it. Like how do you map all the letters to be associated with the keyboard letters. I guess what I''m asking is how the program knows where each letter ends and starts on the bitmap.I know this is done in the utilities page but cant'' see how. Am I in over my head already? Hope I''m just missing a DirctX function or something.

RandomGamer

122

May 02, 2001 05:19 PM

I''ve found that I can download the files if I hold shift while I click the link (open in a new window) but it doesn''t work if I just rightclick on the links and select open in a new window.

Mitijea

122

May 02, 2001 09:43 PM

I've been studying the files from BaseCode1 and on a whim decided to look up the header for windows.h to see what it consisted of. After a fruitless search in the VC++ help files, I tried Microsofts' site.. still nothing definitive. Where can I find a copy of the header? (Microsoft mentions that it is around 8k lines, but not where to get it. The VC++ help eludes to a win32 sdk but nothing comes up in a search on Microsofts site pointing towards my goal.) I guess what I really want to know is: When you include the header, how do you know to include it, and for what reasons? From where do you get this knowledge? Any help would be most appreciated.

Edited by - Mitijea on May 3, 2001 1:02:04 AM

Anonymous

May 03, 2001 01:05 AM

The windows.h header file is in the includes directory. When VC++ compiles one of your source files, the first thing that happens is the precompiler opens all of the #include "..." files. Thus, they must be located on your hard disk somewhere. They are usually located in the c:\devstudio\vc\includes directory, so look in there for windows.h

Later,
Buncen

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shdaga

122

May 03, 2001 01:08 AM

In regards to this file layout for the tuts, where would the code for the AI logic be placed(if any). Just wondering. Keep up the great work.

http://angelfire.com/ny5/codeworx.com

Edited by - shdaga on May 3, 2001 2:10:05 AM

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RandomGamer

122

May 03, 2001 12:02 PM

Also, as far as the 32 bit windows API is concerned, you can find very useful help files on the web that has detailed information about everything in Windows.h. I however cannot find a link to it at the current time, but I do have the help file so I know it exists. I also don''t know if it contains all of the information about Windows.h but I have yet to see a function used that it doesn''t have.

Mitijea

122

May 03, 2001 08:03 PM

Buncen - Thankyou for pointing out where the header is located.. Feeling a little stupid about not figuring it out myself

But after purusing it and the header for winuser.h, I''m even more confused. I know that the includes inside angle brackets don''t nescessarily have to have a corresponding cpp file, but can have another type, such as an exe, or a dll, so I''m not sure where to go from here on finding the original code used in conjunction with the headers. But...
RandomGamer - came up with a good suggestion which I will take up (Thanks

). After looking at the header for winuser, I''m thinking the info I''m looking for could fill volumes. Not really sure if I need to dig that deep, but right now I''m really not comfortable with having to rely on someone else saying to use a function when I''ve no idea where they got it from.. And also, I''m just curious about what I''m missing out on.

darkpunk

122

May 04, 2001 02:54 PM

I have been working with the code and I am beginning to understand the whole modular programming thing now. I''m currently making my own direct x wrapper that will hopefully be made into a library. Thanks teej for the great coding ideas. Especially the ingenious grobals function idea. I look forward to the rest of the tutorial!!!

Anonymous

May 05, 2001 09:57 PM

Rictus,
The resource.bmp file is actually never used. It is just loaded to demonstrate how image files would be laoded in a real game.

The text is painted on the screen using the crude Win32 graphics function TextOut(). As you will see, the font does not even look like the one in the bitmap. It is actually using the default Windows font.
Note: Remember that when you use a Win32 API graphics function like TextOut you must lock your direct draw surfaces and release them when your finished as Teej has done in the example.

Later,
Buncen.

Anonymous

May 05, 2001 10:36 PM

Mitijia,
Don''t think you''ll have much luck finding the ''original code'' that the headers are for. Unless you work at Microsoft or know a good russian hacker. Microsoft do not release the Windows source code to the general public because they think competitors would copy it and they are also terribly embarrased of it.

Later,
Buncen.

04.01 - Some Code to Ponder

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04.01 - Some Code to Ponder

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