windows程序设计中MM_ISOTROPIC怎么使用

Question

#include

#define NUMLINES ((int) (sizeof devcaps / sizeof devcaps [0]))

struct
{
int iIndex ;
TCHAR * szLabel ;
TCHAR * szDesc ;
}
devcaps [] =
{
HORZSIZE, TEXT ("HORZSIZE"), TEXT ("Width in millimeters:"),
VERTSIZE, TEXT ("VERTSIZE"), TEXT ("Height in millimeters:"),
HORZRES, TEXT ("HORZRES"), TEXT ("Width in pixels:"),
VERTRES, TEXT ("VERTRES"), TEXT ("Height in raster lines:"),
BITSPIXEL, TEXT ("BITSPIXEL"), TEXT ("Color bits per pixel:"),
PLANES, TEXT ("PLANES"), TEXT ("Number of color planes:"),
NUMBRUSHES, TEXT ("NUMBRUSHES"), TEXT ("Number of device brushes:"),
NUMPENS, TEXT ("NUMPENS"), TEXT ("Number of device pens:"),
NUMMARKERS, TEXT ("NUMMARKERS"), TEXT ("Number of device markers:"),
NUMFONTS, TEXT ("NUMFONTS"), TEXT ("Number of device fonts:"),
NUMCOLORS, TEXT ("NUMCOLORS"), TEXT ("Number of device colors:"),
PDEVICESIZE, TEXT ("PDEVICESIZE"), TEXT ("Size of device structure:"),
ASPECTX, TEXT ("ASPECTX"), TEXT ("Relative width of pixel:"),
ASPECTY, TEXT ("ASPECTY"), TEXT ("Relative height of pixel:"),
ASPECTXY, TEXT ("ASPECTXY"), TEXT ("Relative diagonal of pixel:"),
LOGPIXELSX, TEXT ("LOGPIXELSX"), TEXT ("Horizontal dots per inch:"),
LOGPIXELSY, TEXT ("LOGPIXELSY"), TEXT ("Vertical dots per inch:"),
SIZEPALETTE, TEXT ("SIZEPALETTE"), TEXT ("Number of palette entries:"),
NUMRESERVED, TEXT ("NUMRESERVED"), TEXT ("Reserved palette entries:"),
COLORRES, TEXT ("COLORRES"), TEXT ("Actual color resolution:")
} ;

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
static TCHAR szAppName[] = TEXT ("DevCaps1") ;
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 ("Device Capabilities"),
                      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 int cxChar, cxCaps, cyChar,cxClient,cyClient,xy,yy;
TCHAR szBuffer[10] ;
HDC hdc ;
int i ;
PAINTSTRUCT ps ;
TEXTMETRIC tm ;

 switch (message)
 {
 case WM_CREATE:
      hdc = GetDC (hwnd) ;
      xy=1000;
      yy=1000;
      SetMapMode(hdc,MM_ISOTROPIC);
      SetWindowExtEx(hdc,xy,yy,NULL);
      SetViewportExtEx(hdc,cxClient,-cyClient,NULL);
      SetViewportOrgEx(hdc,0,cyClient,NULL);
      GetTextMetrics (hdc, &tm) ;
      cxChar = tm.tmAveCharWidth ;
      cxCaps = (tm.tmPitchAndFamily & 1 ? 3 : 2) * cxChar / 2 ;
      cyChar = tm.tmHeight + tm.tmExternalLeading ;

      ReleaseDC (hwnd, hdc) ;

      return 0 ;
 case WM_SIZE:
     cxClient=LOWORD(lParam);
     cyClient=HIWORD(lParam);
     return 0;
 case WM_KEYDOWN:
     switch(wParam)
     {
     case  VK_LEFT:
         xy=xy/2;
         yy=yy/2;
      SetWindowExtEx(hdc,xy,yy,NULL);
          InvalidateRect(hwnd,NULL,TRUE);
          break;
     case  VK_RIGHT:
         xy=xy*2;
         yy=yy*2;
      SetWindowExtEx(hdc,xy,yy,NULL);
          InvalidateRect(hwnd,NULL,TRUE);
          break;
     }
     return 0;
 case WM_PAINT:
      hdc = BeginPaint (hwnd, &ps) ;

      for (i = 0 ; i < NUMLINES ; i++)
      {
           TextOut (hdc, 0, cyChar * i,
                    devcaps[i].szLabel,
                    lstrlen (devcaps[i].szLabel)) ;

           TextOut (hdc, 14 * cxCaps, cyChar * i,
                    devcaps[i].szDesc,
                    lstrlen (devcaps[i].szDesc)) ;

           SetTextAlign (hdc, TA_RIGHT | TA_TOP) ;

           TextOut (hdc, 14 * cxCaps + 35 * cxChar, cyChar * i, szBuffer,
                    wsprintf (szBuffer, TEXT ("%5d"),
                         GetDeviceCaps (hdc, devcaps[i].iIndex))) ;

           SetTextAlign (hdc, TA_LEFT | TA_TOP) ;
      }

      EndPaint (hwnd, &ps) ;
      return 0 ;

 case WM_DESTROY:
      PostQuitMessage (0) ;
      return 0 ;
 }
 return DefWindowProc (hwnd, message, wParam, lParam) ;

}

代码如上，是以windows程序设计第五章的devcaps1程序为例子的，只是在WM_CREATE里加了点，然后加了个wm_keydown，我想实现的效果是：每次按下左箭头，实际上视口逻辑单位缩小一半，那么在上面显示的文字应该放大一倍，但实际上没有变化，我想实现的效果类似于CAD画图时，滚动中键实现图片文字放大缩小的那种效果，请问应该如何才能实现，请知道的告诉下，谢谢了

Answer 1

参考：http://blog.csdn.net/lanyzh0909/article/details/6107814