Game Engine

Source Code for the WinMain Function

Listing 2.2 contains the source code for the game engine's WinMain() function.

Listing 2.2 The WinMain() Function in the Game Engine Makes Calls to Game Engine Functions and Methods and Provides a Neat Way of Separating Standard Windows Program Code from Game Code
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow) {
MSG msg;
static int iTickTrigger = 0;
int iTickCount;
if (GameInitialize(hInstance))
{
// Initialize the game engine
if (!GameEngine::GetEngine()->Initialize(iCmdShow))
return FALSE;
// Enter the main message loop
while (TRUE)
{
if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
{
// Process the message
if (msg.message == WM_QUIT)
break;
TranslateMessage(&msg);
DispatchMessage(&msg);
}
else
{
// Make sure the game engine isn't sleeping
if (!GameEngine::GetEngine()->GetSleep())
{
// Check the tick count to see if a game cycle has elapsed
iTickCount = GetTickCount();
if (iTickCount > iTickTrigger)
{ iTickTrigger = iTickCount +
GameEngine::GetEngine()->GetFrameDelay();
GameCycle();
}
}
}
}
return (int)msg.wParam;
}
// End the game
GameEnd();
return TRUE;
}
Although this WinMain() function is similar to those found in every Windows application, there is an important difference. The difference has to do with the fact that this WinMain() function establishes a game loop that takes care of generating game cycle events at a specified interval. The smallest unit of time measurement in a Windows program is called a tick, which is equivalent to one millisecond and is useful in performing accurate timing tasks. In this case, WinMain() counts ticks in order to determine when it should notify the game that a new cycle is in order. The iTickTrigger and iTickCount variables are used to establish the game cycle timing in WinMain().

The first function called in WinMain() is GameInitialize(), which gives the game a chance to be initialized. Remember that GameInitialize() is a game event function provided as part of the game-specific code for the game; therefore, it isn't a direct part of the game engine. A method that is part of the game engine is Initialize(), which is called to get the game engine itself initialized. From there, WinMain() enters the main message loop for the game program. The else part of the main message loop is where things get interesting. This part of the loop first checks to make sure that the game isn't sleeping and then uses the frame delay for the game engine to count ticks and determine when to call the GameCycle() function to trigger a game cycle event. WinMain() finishes up by calling GameEnd() to give the game program a chance to wrap up the game and clean up after itself. The other standard Windows function included in the game engine is WndProc(), which is very simple because the HandleEvent() method of the GameEngine class is responsible for processing Windows messages:
LRESULT CALLBACK WndProc(HWND hWindow, UINT msg, WPARAM wParam, LPARAM lParam)
{
// Route all Windows messages to the game engine
return GameEngine::GetEngine()->HandleEvent(hWindow, msg, wParam, lParam);
}
All WndProc() really does is pass along all messages to HandleEvent(), which might at first seem like a waste of time. However, the idea is to allow a method of the GameEngine class to handle the messages so that they can be processed in a manner that is consistent with the game engine.
Speaking of the GameEngine class, now that you have a feel for the support functions in the game engine, we can move right along and examine specific code in the GameEngine class. Listing 2.3 contains the source code for the GameEngine() constructor and destructor.

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