获取设备环境的信息

设备环境通常指的是物理的显示设备，如视频显示器或者打印机。经常需要获取这些设备的某些信息，包括显示器的大小（以像素或者物理尺寸的方式）和它的色彩能力。这些信息可以通过调用 GetDeviceCaps 函数来获取：

iValue = GetDeviceCaps(hdc, iIndex); 

其中，参数 iIndex 是定义在 WINGDI.H 头文件中的 29 个标识符之一。

例如，当 iIndex 的值为 HORZRES 时，GetDeviceCaps 函数以像素为单位返回设备的宽度；使用 VERTRES 参数值会以像素为单位返回设备的高度。

如果 hdc 是一个屏幕设备环境的句柄，这里获取的信息和从 GetSystemMetrics 函数获取的信息是一样的。如果 hdc 是一个打印机设备环境，那么 GetDeviceCaps 将以像素为单位返回打印机显示区域的高度和宽度。

还可以使用 GetDeviceCaps 函数来确定设备处理各种类型图形的能力，通常这对于视频显示器并不重要，但是对于打印机却非常重要。例如，大多数的绘图仪不能绘制位图图像，通过调用 GetDeviceCaps 函数可以让你提前知道这一情况。


DEVCAPS1 程序

DEVCAPS1 程序显示了在使用视频显示器设备环境时，可从 GetDeviceCaps 函数得到的部分（并不是全部）信息。

代码如下所示：
 

*---------------------------------------------------------
   DEVCAPS1.C -- Device Capabilities Display Program No. 1
                 (c) Charles Petzold, 1998
  ---------------------------------------------------------*/

#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 ;
     TCHAR       szBuffer[10] ;
     HDC         hdc ;
     int         i ;
     PAINTSTRUCT ps ;
     TEXTMETRIC  tm ;
     
     switch (message)
     {
     case WM_CREATE:
          hdc = GetDC (hwnd) ;
          
          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_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) ;
}