BTNLOOK.C
        
/*--------------------------------------------------------------------------
        
  BTNLOOK.C -- Button Look Program
        
                                         (c) Charles Petzold, 1998
        
---------------------------------------------------------------------------*/
        
#include <windows.h>
        
struct
        
{
        
           int                   iStyle ;
        
           TCHAR *               szText ;
        
}
        
button[] =
        
{
        
           BS_PUSHBUTTON,        TEXT ("PUSHBUTTON"),
        
           BS_DEFPUSHBUTTON,     TEXT ("DEFPUSHBUTTON"),
        
           BS_CHECKBOX,          TEXT ("CHECKBOX"),
        
           BS_AUTOCHECKBOX,         TEXT ("AUTOCHECKBOX"),
        
           BS_RADIOBUTTON,       TEXT ("RADIOBUTTON"),
        
           BS_3STATE,            TEXT ("3STATE"),
        
           BS_AUTO3STATE,        TEXT ("AUTO3STATE"),
        
           BS_GROUPBOX,          TEXT ("GROUPBOX"),
        
           BS_AUTORADIOBUTTON,      TEXT ("AUTORADIO"),
        
           BS_OWNERDRAW,            TEXT ("OWNERDRAW")
        
} ;
        

#define NUM (sizeof button / sizeof button[0])
        
LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;
        
int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
        
                                                         PSTR szCmdLine, int iCmdShow)
        
{
        
           static TCHAR szAppName[] = TEXT ("BtnLook") ;
        
           HWND                                 hwnd ;
        
           MSG                                  msg ;
        
           WNDCLASS                      wndclass ;
        
   
        
           wndclass.style                                       = CS_HREDRAW | CS_VREDRAW ;
        
           wndclass.lpfnWndProc                                 = WndProc ;
        
           wndclass.cbClsExtra                                  = 0 ;
        
           wndclass.cbWndExtra                                  = 0 ;
        
           wndclass.hInstance                                   = hInstance ;
        
           wndclass.hIcon                                       = LoadIcon (NULL, IDI_APPLICATION) ;
        
           wndclass.hCursor            = LoadCursor (NULL, IDC_ARROW) ;
        
           wndclass.hbrBackground              = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
        
           wndclass.lpszMenuName                = NULL ;
        
           wndclass.lpszClassName               = szAppName ;
        
   
        
           if (!RegisterClass (&wndclass))
        
    {
        
                  MessageBox (  NULL, TEXT ("This program requires Windows NT!"),
        
                                                                       szAppName, MB_ICONERROR) ;
        
                  return 0 ;
        
           }
        
   
        
           hwnd = CreateWindow (szAppName, TEXT ("Button Look"),
        
                                  WS_OVERLAPPEDWINDOW,
        
                                  CW_USEDEFAULT, CW_USEDEFAULT,
        
                                 CW_USEDEFAULT, CW_USEDEFAULT,
        
                                  NULL, NULL, hInstance, NULL) ;
        

           ShowWindow (hwnd, iCmdShow) ;
        
           UpdateWindow (hwnd) ;
        

           while (GetMessage (&msg, NULL, 0, 0))
        
         {
        
  TranslateMessage (&msg) ;
        
                         DispatchMessage (&msg) ;
        
           }
        
           return msg.wParam ;
        
}
        

LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
        
{
        
           static HWND           hwndButton[NUM] ;
        
           static RECT           rect ;
        
           static TCHAR          szTop[]       = TEXT ("message   wParam  lParam"),
        
                                          szUnd[]       = TEXT ("_______   ______  ______"),
        
                                          szFormat[]    = TEXT ("%-16s%04X-%04X   %04X-%04X"),
        
                                         szBuffer[50] ;
        
           static int            cxChar, cyChar ;
        
           HDC                                 hdc ;
        
           PAINTSTRUCT           ps ;
        
   int                                  i ;
        
   
        
          switch (message)
        
           {
        
           case   WM_CREATE :
        
                  cxChar = LOWORD (GetDialogBaseUnits ()) ;
        
                  cyChar = HIWORD (GetDialogBaseUnits ()) ;
        
        
        
                  for (i = 0 ; i < NUM ; i++)
        
                                         hwndButton[i] =CreateWindow ( TEXT("button"),button[i].szText,
        
  WS_CHILD | WS_VISIBLE | button[i].iStyle,
        
   cxChar, cyChar * (1 + 2 * i),
        
   20 * cxChar, 7 * cyChar / 4,
        
                              hwnd, (HMENU) i,
        
              ((LPCREATESTRUCT) lParam)->hInstance, NULL) ;
        
                  return 0 ;
        

           case   WM_SIZE :
        
                  rect.left             = 24 * cxChar ;
        
                  rect.top              =  2 * cyChar ;
        
                  rect.right            = LOWORD (lParam) ;
        
                 rect.bottom           = HIWORD (lParam) ;
        
                  return 0 ;
        
           case   WM_PAINT :
        
                  InvalidateRect (hwnd, &rect, TRUE) ;
        
        
        
                  hdc = BeginPaint (hwnd, &ps) ;
        
                  SelectObject (hdc, GetStockObject (SYSTEM_FIXED_FONT)) ;
        
                  SetBkMode (hdc, TRANSPARENT) ;
        
        
        
                  TextOut (hdc, 24 * cxChar, cyChar, szTop, lstrlen (szTop)) ;
        
                 TextOut (hdc, 24 * cxChar, cyChar, szUnd, lstrlen (szUnd)) ;
        
        
        
                  EndPaint (hwnd, &ps) ;
        
                 return 0 ;
        
        
        
           case   WM_DRAWITEM :
        
           case   WM_COMMAND :
        
                  ScrollWindow (hwnd, 0, -cyChar, &rect, &rect) ;
        
        
        
                  hdc = GetDC (hwnd) ;
        
                  SelectObject (hdc, GetStockObject (SYSTEM_FIXED_FONT)) ;
        
       
        
                  TextOut(      hdc, 24 * cxChar, cyChar * (rect.bottom / cyChar - 1),
        
                                                 szBuffer,
        
                                                 wsprintf (szBuffer, szFormat,
        
                                                        message == WM_DRAWITEM ?     TEXT ("WM_DRAWITEM") :
        
                                          TEXT ("WM_COMMAND"),
        
                                                        HIWORD (wParam), LOWORD (wParam),
        
                                                         HIWORD (lParam), LOWORD (lParam))) ;
        
        
        
                 ReleaseDC (hwnd, hdc) ;
        
                  ValidateRect (hwnd, &rect) ;
        
                  break ;
        
        
        
           case   WM_DESTROY :
        
                  PostQuitMessage (0) ;
        
                  return 0 ;
        
    }
        
           return DefWindowProc (hwnd, message, wParam, lParam) ;
        
}



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这段代码里面ScrollWindow (hwnd, 0, -cyChar, &rect, &rect) 是怎么工作的啊
他不是结束后产生WM_PAINT消息?
那怎么不是会使开始输出的内容刷新了吗, 运行的时候怎么不是这样的,
那位高手能解释一下,ScrollWindow (hwnd, 0, -cyChar, &rect, &rect) 是怎么工作的?