實時消息抽取循環

     怎樣在屏幕上連續不斷顯示圖形來催眠用戶呢?僅用GetMessage()是辦不到的。
如果消息隊列中沒有消息，GetMessage()就會等待，直到新的消息出現在隊列中。
因爲許多遊戲是充滿動作的，需要猛擊鍵盤，產生場景變化，利用簡單的GetMessage()
通常不能符合要求，遊戲編程者不希望玩家在沒有新的動作是遊戲靜止不動，他們希望
怪獸從後面衝出來，圍攻玩家，追捕玩家。爲了做到這樣的效果，需要這樣一種消息
循環：只有遇到需要處理的消息時纔去處理消息，其餘的時間都讓遊戲代碼自動產生
激烈的場面。爲了做到這一點需要用到PeekMessage()函數。
PeekMessage (From MSDN)
The PeekMessage function checks a thread message queue for a message and
places the message (if any) in the specified structure.

BOOL PeekMessage(
  LPMSG lpMsg,         // pointer to structure for message
  HWND hWnd,           // handle to window
  UINT wMsgFilterMin,  // first message
  UINT wMsgFilterMax,  // last message
  UINT wRemoveMsg      // removal flags
);

PeekMessage()函數和GetMessage()函數很相,惟一不同的是最後個參數: wRemoveMsg;
它的值可以是: PM_NOREMOVE--表示消息處理後仍留在消息隊列中;
PM_REMOVE--表示消息處理後從隊列中移去。 通常選擇使用後者。
    若隊列中有消息，PeekMessage()將返回true;
    若隊列中無消息，PeekMessage()將返回false;
要創建實時消息的抽取循環,就需要更復雜一些. 若只是簡單的把GetMessage()替換爲
PeekMessage(), 則當隊列中沒有消息時,程序將會一閃而過. 因此實際的程序中需要
更強健的設計.
//----------------------------------------------------------------------------- // Copyright (c) 2009 eryar All rights reserved. // // File : main.cpp // Author : [e-mail] // Date : // Version : 1.0v // // Description : // //============================================================================= #include <time.h> #include <windows.h> char* g_szAppName = "Cute Bubble"; inline int RandInt(int x, int y) {return rand() % (y - x +1) +x; } LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd) { MSG Msg; HWND hWnd; WNDCLASS wc; bool bFlag = false; char* szClassName = "CPeekMessage"; wc.style = CS_HREDRAW|CS_VREDRAW; wc.lpfnWndProc = WndProc; wc.cbClsExtra = 0; wc.cbWndExtra = 0; wc.hInstance = hInstance; wc.hIcon = LoadIcon(NULL, IDI_APPLICATION); wc.hCursor = LoadCursor(NULL, IDC_ARROW); wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH); wc.lpszMenuName = NULL; wc.lpszClassName = szClassName; if (!RegisterClass(&wc)) { MessageBox(NULL, "register window class failed! ", g_szAppName, MB_OK|MB_ICONERROR); return false; } hWnd = CreateWindow( szClassName, g_szAppName, WS_OVERLAPPEDWINDOW, 0,0, 300, 300, NULL, NULL, hInstance, NULL); if (!hWnd) { MessageBox(NULL, "create window failed! ", g_szAppName, MB_OK|MB_ICONERROR); return false; } ShowWindow(hWnd, nShowCmd); UpdateWindow(hWnd); while (!bFlag) { while(PeekMessage(&Msg, NULL, 0, 0, PM_REMOVE)) { if (Msg.message == WM_QUIT) { bFlag = true; } else { TranslateMessage(&Msg); DispatchMessage(&Msg); } } // This will call WM_PAINT which well render our scene InvalidateRect(hWnd, NULL, true); UpdateWindow(hWnd); Sleep(8); } return Msg.wParam; } LRESULT CALLBACK WndProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam) { switch(Msg) { case WM_CREATE: srand((unsigned)time(NULL)); return false; case WM_PAINT: RECT rect; POINT point; HBRUSH RandBrush; HBRUSH OldBrush; PAINTSTRUCT ps; int radius; BeginPaint(hWnd, &ps); // create a random brush RandBrush = CreateSolidBrush(RGB(RandInt(0, 255), RandInt(0, 255), RandInt(0, 255))); OldBrush = (HBRUSH)SelectObject(ps.hdc, RandBrush); GetClientRect(hWnd, &rect); point.x = rect.right; point.y = rect.bottom; point.x = RandInt(0, point.x); point.y = RandInt(0, point.y); radius = RandInt(0, 100); Ellipse(ps.hdc, point.x-radius, point.y-radius, point.x+radius, point.y+radius); SelectObject(ps.hdc, OldBrush); EndPaint(hWnd, &ps); return false; case WM_DESTROY: PostQuitMessage(0); return false; default: return DefWindowProc(hWnd, Msg, wParam, lParam); } } // WndProc