Creating an Engine for Games for Windows - Resource.h Header File
(Page 10 of 11 )
Listing 2.9 The Resource.h Header File Declares Identifiers for Icons Used in the Blizzard Example
//————————————————————————————————-
// Icons Range : 1000 - 1999
//————————————————————————————————-
#define IDI_BLIZZARD 1000
#define IDI_BLIZZARD_SM 1001
Resources are typically numbered in certain ranges to make it easier to distinguish them from each other and to help ensure that they have unique values. As you get into more interesting examples throughout the book, you'll be adding additional types of resources to the Resource.h header file, such as bitmap images and wave sound resources.
Speaking of resources, the icons in the Blizzard example are listed in the Blizzard.rc resource script, which is shown in Listing 2.10.
Listing 2.10 The Blizzard.rc Resource Script Lists Icon Resources Used in the Blizzard Example
#include "Resource.h"
//————————————————————————————————-
// Icons
//————————————————————————————————-
IDI_BLIZZARD ICON "Res\\Blizzard.ico"
IDI_BLIZZARD_SM ICON "Res\\Blizzard_sm.ico"
The Blizzard.rc resource script is where the resource identifiers in the Resource.h file are linked to actual resource files. In this example, the resource files are icon files, which is evident by their .ICO file extension. When you compile the Blizzard example, the resources listed in the Blizzard.rc resource script are compiled into binary form and are linked into the Blizzard.exe executable.
Now that you've gotten a look at the helper files that go into the Blizzard example, let's move on to the main source code. The main Blizzard program is fleshed out in the Blizzard.cpp source code file, which is shown in Listing 2.11
Listing 2.11 The Blizzard.cpp Source Code File Reveals how Straightforward the Program Code for a Minimal Windows Program (Game) Becomes when a Game Engine Is Used
//————————————————————————————————-
// Blizzard Application
// C++ Source - Blizzard.cpp
//————————————————————————————————-
//————————————————————————————————-
// Include Files
//————————————————————————————————-
#include "Blizzard.h"
//————————————————————————————————-
// Game Engine Functions
//————————————————————————————————-
BOOL GameInitialize(HINSTANCE hInstance)
{
// Create the game engine
g_pGame = new GameEngine(hInstance, TEXT("Blizzard"),
TEXT("Blizzard"), IDI_BLIZZARD, IDI_BLIZZARD_SM);
if (g_pGame == NULL)
return FALSE;
// Set the frame rate
g_pGame->SetFrameRate(15);
return TRUE;
}
void GameStart(HWND hWindow)
{
// Seed the random number generator
srand(GetTickCount());
}
void GameEnd()
{
// Cleanup the game engine
delete g_pGame;
}
void GameActivate(HWND hWindow)
{
HDC hDC;
RECT rect;
// Draw activation text on the game screen
GetClientRect(hWindow, &rect);
hDC = GetDC(hWindow);
DrawText(hDC, TEXT("Here comes the blizzard!"), -1, &rect,
DT_SINGLELINE | DT_CENTER | DT_VCENTER);
ReleaseDC(hWindow, hDC);
}
void GameDeactivate(HWND hWindow)
{
HDC hDC;
RECT rect;
// Draw deactivation text on the game screen
GetClientRect(hWindow, &rect);
hDC = GetDC(hWindow);
DrawText(hDC, TEXT("The blizzard has passed."), -1, &rect,
DT_SINGLELINE | DT_CENTER | DT_VCENTER);
ReleaseDC(hWindow, hDC);
}
void GamePaint(HDC hDC)
{
}
void GameCycle()
{
HDC hDC;
HWND hWindow = g_pGame->GetWindow();
// Draw the snowflake icon at random positions on the game screen
hDC = GetDC(hWindow);
DrawIcon(hDC, rand() % g_pGame->GetWidth(), rand() % g_pGame->GetHeight(),
(HICON)(WORD)GetClassLong(hWindow, GCL_HICON));
ReleaseDC(hWindow, hDC);
}
The really interesting thing about the code for the Blizzard example is how the only functions present in the code are the game event functions described in GameEngine.h (refer to Listing 2.6). The first of these functions is GameInitialize(), whose responsibility is to get the program started off on the right foot. More specifically, the GameInitialize() function creates a GameEngine object and assigns it to the g_pGame global variable. The GameInitialize() function then sets the frame rate for the game to 15 frames per second, which is a little slower than the default setting of 20 frames per second. This change is primarily to demonstrate how you will often change the default frame rate for games depending on their specific needs.
The GameStart() function is next, and its job is to initialize game data and start a game. In the case of the Blizzard example, there really isn't any game data, so the only code in GameStart() is code to seed a random number generator. I mentioned earlier that the Blizzard example draws snowflake icons at random positions on the screen. In order to successfully generate random numbers for these positions, you have to seed the random number generator. This is accomplished with a call to the standard C library function, srand().
Note - Random number generators don't truly generate random numbers. Instead, they generate a pattern of numbers that has the appearance of being random if you make sure that the pattern is selected differently each time a program is run. This is accomplished by seeding the random number generator with an unpredictable value. It turns out that the internal Windows tick count changes so rapidly that if you look at it at any given instant, you will generally get a unique value, which is sufficient to seed the random number generator and get "random" results.
Similar to the GameStart() function, the GameEnd() function is designed to clean up game data once a game is over. In this case, the GameEnd() function is only required to clean up the game engine.
The GameActivate() and GameDeactivate() functions are very similar to each other in the Blizzard example. Both are here just to demonstrate how you can respond to game activations and deactivations, and they do so by drawing text on the game screen. For example, the GameActivate() function obtains the client rectangle for the game window and then uses it as the basis for drawing a line of text centered on the game screen. I realize that some of this graphics code probably looks a little strange, but don't worry too much about it because the next chapter gives you the whole scoop on how to draw graphics in Windows. Speaking of strange graphics code, the GamePaint() function is responsible for painting the game screen, but in this case, all the painting takes place in the GameCycle() function, so GamePaint() does nothing.
The GameCycle() function is the last function in the Blizzard example and is, without a doubt, the most interesting. The job of this function is to draw a snowflake icon at a random location on the game screen. This might not seem like a big deal, but keep in mind that you set the frame rate to 15 frames per second, which means that the GameCycle() function is getting called 15 times every second; this means that 15 icons get drawn in random locations every second! The first step in the GameCycle() function is to obtain a window handle for the main game window; this window handle is important because it allows you to draw on the game screen. The drawing actually takes place when the Win32 DrawIcon() function is called to draw the Blizzard icon. The standard rand() function is called to determine a random location on the game screen, and the icon is extracted from the game window class using the Win32 GetClassLong() function.
Note - I used a little trick in this example to avoid the task of loading and drawing bitmap images. Because a Windows application's icon is automatically loaded into its window class, I chose to draw the icon, as opposed to loading a bitmap image and drawing it. You learn how to load and draw a bitmap image in Chapter 4, "Drawing Graphical Images," but for now, drawing an icon proved much simpler.
Although I admittedly threw you a few curves with the graphics code in the Blizzard example, hopefully, you were able to follow along with most of the code. You were also hopefully able to see the benefit of relying on the game engine to take care of a lot of the dirty work associated with Windows game programming.
 This chapter is from Beginning Game Programming, by Michael Morrison (Sams, ISBN: 0672326590). Check it out at your favorite bookstore today.
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