在剛開始學習遊戲程式設計入門(beginning game programming)時，會發現對書中的程式碼非常的陌生，心裡沒有底的感覺，後來無意間看了孫鑫老師的C++教程前兩章，才發現許多程式碼是C++應用程式中固定的寫法，視窗程式設計中的建立視窗的步驟也是固定的，在回來看遊戲程式設計入門時，發現遊戲引擎就是吧一般應用程式所要做的事情放到遊戲引擎中，把初始化和訊息的方法傳遞到特定的方法中，由程式的其他部分來實現。感覺對引擎的認識更提高了一步，廢話不多說，上例子說明：

遊戲引擎標頭檔案(GameEngine.h)

#pragma once //----------------------------------------------------------------- // Include Files //----------------------------------------------------------------- #include <windows.h> //----------------------------------------------------------------- // Windows Function Declarations //----------------------------------------------------------------- int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow); LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam); //----------------------------------------------------------------- // Game Engine 函式宣告部分，遊戲只要實現以下方法就可以了//----------------------------------------------------------------- BOOL GameInitialize(HINSTANCE hInstance); void GameStart(HWND hWindow); void GameEnd(); void GameActivate(HWND hWindow); void GameDeactivate(HWND hWindow); void GamePaint(HDC hDC); void GameCycle(); void HandleKeys(); void MouseButtonDown(int x, int y, BOOL bLeft); void MouseButtonUp(int x, int y, BOOL bLeft); void MouseMove(int x, int y); //----------------------------------------------------------------- // GameEngine Class 引擎類 //----------------------------------------------------------------- class GameEngine { protected: // Member Variables static GameEngine* m_pGameEngine; HINSTANCE m_hInstance; HWND m_hWindow; TCHAR m_szWindowClass[32]; TCHAR m_szTitle[32]; WORD m_wIcon, m_wSmallIcon; int m_iWidth, m_iHeight; int m_iFrameDelay; BOOL m_bSleep; public: // Constructor(s)/Destructor GameEngine(HINSTANCE hInstance, LPTSTR szWindowClass, LPTSTR szTitle, WORD wIcon, WORD wSmallIcon, int iWidth = 640, int iHeight = 480); virtual ~GameEngine(); // General Methods static GameEngine* GetEngine() { return m_pGameEngine; }; BOOL Initialize(int iCmdShow); LRESULT HandleEvent(HWND hWindow, UINT msg, WPARAM wParam, LPARAM lParam); void ErrorQuit(LPTSTR szErrorMsg); // Accessor Methods HINSTANCE GetInstance() { return m_hInstance; }; HWND GetWindow() { return m_hWindow; }; void SetWindow(HWND hWindow) { m_hWindow = hWindow; }; LPTSTR GetTitle() { return m_szTitle; }; WORD GetIcon() { return m_wIcon; }; WORD GetSmallIcon() { return m_wSmallIcon; }; int GetWidth() { return m_iWidth; }; int GetHeight() { return m_iHeight; }; int GetFrameDelay() { return m_iFrameDelay; }; void SetFrameRate(int iFrameRate) { m_iFrameDelay = 1000 / iFrameRate; }; BOOL GetSleep() { return m_bSleep; }; void SetSleep(BOOL bSleep) { m_bSleep = bSleep; }; };

這個是書上的例子，主要是看Windows Function Declarations這個部分，就是windows函式申明，在應用程式中本來就是以WinMain做入口的，這裡放到引擎類中來實現。下面是GameEngine.cpp檔案中的WinMain部分：

//----------------------------------------------------------------- // Windows Functions //----------------------------------------------------------------- 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(); HandleKeys(); GameCycle(); } } } } return (int)msg.wParam; } // End the game GameEnd(); return TRUE; }

重點是GameInitialize(hInstance)方法和

if (!GameEngine::GetEngine()->Initialize(iCmdShow))
      return FALSE;

這兩行程式碼，具體檢視裡面的程式碼是這樣的：

//----------------------------------------------------------------- // Game Engine Functions //----------------------------------------------------------------- BOOL GameInitialize(HINSTANCE hInstance) { // Create the game engine g_pGame = new GameEngine(hInstance, TEXT("Brainiac"), TEXT("Brainiac"), IDI_BRAINIAC, IDI_BRAINIAC_SM, 528, 512); if (g_pGame == NULL) return FALSE; // Set the frame rate g_pGame->SetFrameRate(1); // Store the instance handle g_hInstance = hInstance; return TRUE; }

//----------------------------------------------------------------- // Game Engine General Methods //----------------------------------------------------------------- BOOL GameEngine::Initialize(int iCmdShow) { WNDCLASSEX wndclass; // Create the window class for the main window wndclass.cbSize = sizeof(wndclass); wndclass.style = CS_HREDRAW | CS_VREDRAW; wndclass.lpfnWndProc = WndProc; wndclass.cbClsExtra = 0; wndclass.cbWndExtra = 0; wndclass.hInstance = m_hInstance; wndclass.hIcon = LoadIcon(m_hInstance, MAKEINTRESOURCE(GetIcon())); wndclass.hIconSm = LoadIcon(m_hInstance, MAKEINTRESOURCE(GetSmallIcon())); wndclass.hCursor = LoadCursor(NULL, IDC_ARROW); wndclass.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1); wndclass.lpszMenuName = NULL; wndclass.lpszClassName = m_szWindowClass; // Register the window class if (!RegisterClassEx(&wndclass)) return FALSE; // Calculate the window size and position based upon the game size int iWindowWidth = m_iWidth + GetSystemMetrics(SM_CXFIXEDFRAME) * 2, iWindowHeight = m_iHeight + GetSystemMetrics(SM_CYFIXEDFRAME) * 2 + GetSystemMetrics(SM_CYCAPTION); if (wndclass.lpszMenuName != NULL) iWindowHeight += GetSystemMetrics(SM_CYMENU); int iXWindowPos = (GetSystemMetrics(SM_CXSCREEN) - iWindowWidth) / 2, iYWindowPos = (GetSystemMetrics(SM_CYSCREEN) - iWindowHeight) / 2; // Create the window m_hWindow = CreateWindow(m_szWindowClass, m_szTitle, WS_POPUPWINDOW | WS_CAPTION | WS_MINIMIZEBOX, iXWindowPos, iYWindowPos, iWindowWidth, iWindowHeight, NULL, NULL, m_hInstance, NULL); if (!m_hWindow) return FALSE; // Show and update the window ShowWindow(m_hWindow, iCmdShow); UpdateWindow(m_hWindow); return TRUE; }

GameInitialize方法是例項化遊戲引擎類，並初始化一些引數，而Initialize方法則讓我一開始摸不著頭腦，這些程式碼書中並沒有具體的解釋為什麼，如果知道C++應用程式的視窗建立，那麼這段程式碼是再熟悉不過的了，就像標準寫法一樣：申明視窗、設計視窗、註冊視窗、現實視窗、重新整理視窗。遊戲引擎類巧妙的將這些固定的程式碼放在引擎中初始化了，而且可以很好的進行復用。

再回頭看看WinMain程式碼中的：

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(); HandleKeys(); GameCycle(); } } } }

發現這就是標準API程式碼中訊息迴圈處理的程式碼，不同的是訊息處理迴圈中加上了遊戲引擎獨特的時間片操作處理部分，這樣設計讓遊戲引擎的功能更加完整。

小結

國外的這些參考書買來直接啃，有時候會消化不良，和我們原來學校中看的教材相差太大了，這些實用性較高的參考書籍，已經撇開了許多瑣碎的基礎知識，直接就上和書本有關係的資訊，對讀者有一定基礎的要求，閱讀這類書時還真的自己花時間補下基礎，再回頭看書，效果會十分明顯。