第017讲：获取设备环境的信息（课文解读）
以下解读来自《Windows 程序设计》（第5版 珍藏版）P105~108小甲鱼解读：内容比较简单，无需过多解读，看过了就懂了~
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 <windows.h>
#define NUMLINES ((int) (sizeof devcaps / sizeof devcaps ))
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 intcxChar, cxCaps, cyChar ;
TCHAR szBuffer ;
HDC hdc ;
int i ;
PAINTSTRUCT ps ;
TEXTMETRICtm ;
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.szLabel,
lstrlen (devcaps.szLabel)) ;
TextOut (hdc, 14 * cxCaps, cyChar * i,
devcaps.szDesc,
lstrlen (devcaps.szDesc)) ;
SetTextAlign (hdc, TA_RIGHT | TA_TOP) ;
TextOut (hdc, 14 * cxCaps + 35 * cxChar, cyChar * i, szBuffer,
wsprintf (szBuffer, TEXT ("%5d"),
GetDeviceCaps (hdc, devcaps.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) ;
}
WinSDK
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