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

pazu

122

May 23, 2001 10:16 PM

Mortation: The magic is in the extern keyword. Look that there is something like this in the globals.h file:

#ifndef GLOBALS_OWNERSHIPextern#endifstruct G...

So, every file EXCEPT the one which defines GLOBAL_OWNERSHIP (which is gamemain.cpp) gets an external reference to G.

This was a nice trick, Teej!

Ja ne, Pazu mailto: pazu@animegaiden.com.brClose the world, open the neXt

Mortation

122

May 24, 2001 12:41 AM

So if I was to do
#ifndef INPUT_OWNERSHIP
extern
#endif
struct M

and call
#define INPUT_OWNERSHIP in input.cpp
I will be ok? No more already defined errors?

V^^^V
** |Mortation| **
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MortÔ¿Ô¬

Anonymous

May 25, 2001 05:26 PM

Teej: I believe the problem is by solved now. Like Pezy says, the BaseCode1 project is written in C++, but without the OO concepts... My code was in _pure_ C, and that was why I couldn''t get it to work (by doing it the way you did).

\JWA

Anonymous

May 29, 2001 07:34 AM

Anyone kind enough to post somewhere BaseCode1.zip?

Seems that WebJump''s less than reliable and I''m unable to dig into the tutorial (though excellent as they may be) without ''em.

Thanks in advance!

superpig

1,826

June 06, 2001 03:32 PM

Anon - are you sure you've got your second and third parameters round the right way?

Teej - There was an article recently about using multiple threads. Would it be a good idea to put Game_Main() in a seperate thread? I understand that you don't want to clutter the tutorial with Win32 code, but in my own programs...?

Superpig
- saving pigs from untimely fates

Edited by - superpig on June 6, 2001 4:39:40 PM

Richard "Superpig" Fine - saving pigs from untimely fates - Microsoft DirectX MVP 2006/2007/2008/2009
"Shaders are not meant to do everything. Of course you can try to use it for everything, but it's like playing football using cabbage." - MickeyMouse

Anonymous

June 20, 2001 01:24 PM

I''m afraid i must be showing up a few months too late...
it seems all of the code examples have gone missing (even
at the second URL posted below).

does anyone know where i can find this stuff?