学步园

     怎样在屏幕上连续不断显示图形来催眠用户呢?仅用GetMessage()是办不到的。
如果消息队列中没有消息，GetMessage()就会等待，直到新的消息出现在队列中。
因为许多游戏是充满动作的，需要猛击键盘，产生场景变化，利用简单的GetMessage()
通常不能符合要求，游戏编程者不希望玩家在没有新的动作是游戏静止不动，他们希望
怪兽从后面冲出来，围攻玩家，追捕玩家。为了做到这样的效果，需要这样一种消息
循环：只有遇到需要处理的消息时才去处理消息，其余的时间都让游戏代码自动产生
激烈的场面。为了做到这一点需要用到PeekMessage()函数。
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()函数和GetMessage()函数很相,惟一不同的是最后个参数: wRemoveMsg;
它的值可以是: PM_NOREMOVE--表示消息处理后仍留在消息队列中;
PM_REMOVE--表示消息处理后从队列中移去。 通常选择使用后者。
    若队列中有消息，PeekMessage()将返回true;
    若队列中无消息，PeekMessage()将返回false;
要创建实时消息的抽取循环,就需要更复杂一些. 若只是简单的把GetMessage()替换为
PeekMessage(), 则当队列中没有消息时,程序将会一闪而过. 因此实际的程序中需要
更强健的设计.
//-----------------------------------------------------------------------------<br /> // Copyright (c) 2009 eryar All rights reserved.<br /> //<br /> // File : main.cpp<br /> // Author : eryar@163.com<br /> // Date :<br /> // Version : 1.0v<br /> //<br /> // Description :<br /> //<br /> //=============================================================================</p> <p>#include <time.h><br /> #include <windows.h></p> <p>char* g_szAppName = "Cute Bubble";</p> <p>inline int RandInt(int x, int y) {return rand() % (y - x +1) +x; }<br /> LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);<br /> int WINAPI WinMain(HINSTANCE hInstance,<br /> HINSTANCE hPrevInstance,<br /> LPSTR lpCmdLine,<br /> int nShowCmd)<br /> {<br /> MSG Msg;<br /> HWND hWnd;<br /> WNDCLASS wc;<br /> bool bFlag = false;<br /> char* szClassName = "CPeekMessage";</p> <p> wc.style = CS_HREDRAW|CS_VREDRAW;<br /> wc.lpfnWndProc = WndProc;<br /> wc.cbClsExtra = 0;<br /> wc.cbWndExtra = 0;<br /> wc.hInstance = hInstance;<br /> wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);<br /> wc.hCursor = LoadCursor(NULL, IDC_ARROW);<br /> wc.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);<br /> wc.lpszMenuName = NULL;<br /> wc.lpszClassName = szClassName;</p> <p> if (!RegisterClass(&wc)) {<br /> MessageBox(NULL, "register window class failed! ", g_szAppName, MB_OK|MB_ICONERROR);<br /> return false;<br /> }</p> <p> hWnd = CreateWindow(<br /> szClassName,<br /> g_szAppName,<br /> WS_OVERLAPPEDWINDOW,<br /> 0,0,<br /> 300, 300,<br /> NULL,<br /> NULL,<br /> hInstance,<br /> NULL);</p> <p> if (!hWnd) {<br /> MessageBox(NULL, "create window failed! ", g_szAppName, MB_OK|MB_ICONERROR);<br /> return false;<br /> }</p> <p> ShowWindow(hWnd, nShowCmd);<br /> UpdateWindow(hWnd);</p> <p> while (!bFlag) {<br /> while(PeekMessage(&Msg, NULL, 0, 0, PM_REMOVE)) {</p> <p> if (Msg.message == WM_QUIT) {<br /> bFlag = true;<br /> }<br /> else {<br /> TranslateMessage(&Msg);<br /> DispatchMessage(&Msg);<br /> }<br /> }</p> <p> // This will call WM_PAINT which well render our scene<br /> InvalidateRect(hWnd, NULL, true);<br /> UpdateWindow(hWnd);<br /> Sleep(8);<br /> }</p> <p> return Msg.wParam;<br /> }</p> <p>LRESULT CALLBACK WndProc(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam) {</p> <p> switch(Msg) {<br /> case WM_CREATE:<br /> srand((unsigned)time(NULL));<br /> return false;</p> <p> case WM_PAINT:<br /> RECT rect;<br /> POINT point;<br /> HBRUSH RandBrush;<br /> HBRUSH OldBrush;<br /> PAINTSTRUCT ps;<br /> int radius;</p> <p> BeginPaint(hWnd, &ps);</p> <p> // create a random brush<br /> RandBrush = CreateSolidBrush(RGB(RandInt(0, 255), RandInt(0, 255), RandInt(0, 255)));<br /> OldBrush = (HBRUSH)SelectObject(ps.hdc, RandBrush);</p> <p> GetClientRect(hWnd, &rect);<br /> point.x = rect.right;<br /> point.y = rect.bottom;</p> <p> point.x = RandInt(0, point.x);<br /> point.y = RandInt(0, point.y);<br /> radius = RandInt(0, 100);</p> <p> Ellipse(ps.hdc, point.x-radius, point.y-radius, point.x+radius, point.y+radius);</p> <p> SelectObject(ps.hdc, OldBrush);<br /> EndPaint(hWnd, &ps);<br /> return false;</p> <p> case WM_DESTROY:<br /> PostQuitMessage(0);<br /> return false;</p> <p> default:<br /> return DefWindowProc(hWnd, Msg, wParam, lParam);<br /> }<br /> } // WndProc