五、GDI映像方式—WHATSIZE程序
Windows的小历史：第一篇如何写作Windows程序的介绍文章出现在《Microsoft Systems Journal》1986年12月号上。在那篇文章中，范例程序叫做WSZ（「what size：什么尺寸」），它以图素、英寸和毫米为单位显示了显示区域的大小。那个程序的更简易版本是WHATSIZE，如程序5-6所示。程序显示了以五种度量映像方式显示的窗口显示区域的大小。
程序5-6 WHATSIZE
WHATSIZE.C
/*------------------------------------------------------------
WHATSIZE.C -- What Size is the Window?
(c) Charles Petzold, 1998
----------------------------------------------------------*/
#include <windows.h>
LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;
int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
static TCHAR szAppName[] = TEXT ("WhatSize") ;
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 ("What Size is the Window?"),
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 ;
}
void Show (HWND hwnd, HDC hdc, int xText, int yText, int iMapMode,
TCHAR * szMapMode)
{
TCHAR szBuffer [60] ;
RECT rect ;
SaveDC (hdc) ;
SetMapMode (hdc, iMapMode) ;
GetClientRect (hwnd, &rect) ;
DPtoLP (hdc, (PPOINT) &rect, 2) ;
RestoreDC (hdc, -1) ;
TextOut ( hdc, xText, yText, szBuffer,
wsprintf (szBuffer, TEXT ("%-20s %7d %7d %7d %7d"), szMapMode,
rect.left, rect.right, rect.top, rect.bottom)) ;
}
LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
static TCHAR szHeading [] =
TEXT ("Mapping Mode Left Right Top Bottom") ;
static TCHAR szUndLine [] =
TEXT ("------------ ---- ----- --- ------") ;
static int cxChar, cyChar ;
HDC hdc ;
PAINTSTRUCT ps ;
TEXTMETRIC tm ;
switch (message)
{
case WM_CREATE:
hdc = GetDC (hwnd) ;
SelectObject (hdc, GetStockObject (SYSTEM_FIXED_FONT)) ;
GetTextMetrics (hdc, &tm) ;
cxChar = tm.tmAveCharWidth ;
cyChar = tm.tmHeight + tm.tmExternalLeading ;
ReleaseDC (hwnd, hdc) ;
return 0 ;
case WM_PAINT:
hdc = BeginPaint (hwnd, &ps) ;
SelectObject (hdc, GetStockObject (SYSTEM_FIXED_FONT)) ;
SetMapMode (hdc, MM_ANISOTROPIC) ;
SetWindowExtEx (hdc, 1, 1, NULL) ;
SetViewportExtEx (hdc, cxChar, cyChar, NULL) ;
TextOut (hdc, 1, 1, szHeading, lstrlen (szHeading)) ;
TextOut (hdc, 1, 2, szUndLine, lstrlen (szUndLine)) ;
Show (hwnd, hdc, 1, 3, MM_TEXT, TEXT ("TEXT (pixels)")) ;
Show (hwnd, hdc, 1, 4, MM_LOMETRIC, TEXT ("LOMETRIC (.1 mm)")) ;
Show (hwnd, hdc, 1, 5, MM_HIMETRIC, TEXT ("HIMETRIC (.01 mm)")) ;
Show (hwnd, hdc, 1, 6, MM_LOENGLISH, TEXT ("LOENGLISH (.01 in)")) ;
Show (hwnd, hdc, 1, 7, MM_HIENGLISH,TEXT ("HIENGLISH (.001 in)")) ;
Show (hwnd, hdc, 1, 8, MM_TWIPS, EXT ("TWIPS (1/1440 in)")) ;
EndPaint (hwnd, &ps) ;
return 0 ;
case WM_DESTROY:
PostQuitMessage (0) ;
return 0 ;
}
return DefWindowProc (hwnd, message, wParam, lParam) ;
}
为了便于用TextOut函数显示信息，WHATSIZE使用了一种固定间距的字体。下面一条简单的叙述就可以切换为固定间距的字体（在Windows 3.0中它是优先使用的）：
SelectObject (hdc, GetStockObject (SYSTEM_FIXED_FONT)) ;
有两个同样的函数用于选取画笔和画刷。像前面提到的，WHATSIZE也使用MM_ANISTROPIC映像方式将逻辑单位设定为字符大小。
当WHATSIZE需要取得六种映像方式之一的显示区域的大小时，它保存目前的设备内容，设定一种新的映像方式，取得显示区域坐标，将它们转换为逻辑坐标，然后在显示信息之前，恢复原映像方式。底下这些程序代码在WHATSIZE的Show函数里：
SaveDC (hdc) ;
SetMapMode (hdc, iMapMode) ;
GetClientRect (hwnd, &rect) ;
DptoLP (hdc, (PPOINT) &rect, 2) ;
RestoreDC (hdc, -1) ;
图5-19显示了WHATSIZE的典型输出。
