Q113254: INFO: Calculating MM_HIMETRIC Units for the METAFILEPICT
Article: Q113254
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1
Operating System(s):
Keyword(s): kbSDKWin16
Last Modified: 26-JUN-1999
3.10
WINDOWS
kbprg
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The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1
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SUMMARY
=======
To copy a Windows metafile to the clipboard, it is necessary to allocate memory
for a METAFILEPICT structure and fill it out appropriately. This article shows
one approach to filling out the METAFILEPICT structure when you want to provide
a suggested size for playing back the metafile in addition to having it be
scalable.
MORE INFORMATION
================
The first step in copying the metafile to the clipboard is to allocate global
memory for the METAFILEPICT structure. After copying this structure to the
clipboard, the memory that you allocated for the METAFILEPICT structure is owned
by the clipboard and you should not lock it or modify it.
The METAFILEPICT structure is defined as follows:
typedef struct tagMETAFILEPICT
{
int mm;
int xExt;
int yExt;
HMETAFILE hMF;
} METAFILEPICT;
The mm field in the METAFILEPICT structure specifies the mapping mode in which
the metafile is to be played. In order for your metafile to be scalable, you
should specify MM_ANISOTROPIC as the mapping mode for the mm field. The members
xExt and yExt specify the width and height of the rectangle within which the
metafile is played.
When the mapping mode is MM_ANISOTROPIC, the values for xExt and yExt should be
in MM_HIMETRIC units. Of course you can always calculate the values yourself,
but it's very easy to use the functions LPtoDP and DPtoLP to let Windows do the
calculation for you. The LPtoDP function converts logical points to device
points; DPtoLP converts device points to logical points.
You need a handle to a device context (hDC) compatible with the display in order
to do the conversion. There are many ways to obtain a display hDC. The functions
GetDC(NULL), CreateCompatibleDC(NULL), CreateDC("DISPLAY", NULL, NULL, NULL),
GetDC(hWnd), and GetWindowDC(hWnd) all return a suitable display hDC.
If you call any of the above functions to obtain an hDC, unless you explicitly
change the mapping mode, it is in the default mapping mode, MM_TEXT. In the
MM_TEXT mapping mode, one logical unit equals one device unit.
If you used the MM_TEXT mapping mode to create your metafile, then it is quite
likely that you will also know the width and height of your metafile in device
units (pixels). In this case, to calculate values for xExt and yExt, just
temporarily set the mapping mode to MM_HIMETRIC and call the function DPtoLP to
convert the device units to MM_HIMETRIC units. For example:
pt.x = nWidth;
pt.y = nHeight;
SaveDC(hDC);
SetMapMode(hDC, MM_HIMETRIC);
DPtoLP(hDC, &pt, 1);
RestoreDC(hDC, -1);
Because the y-axis is inverted in the MM_HIMETRIC mapping mode, DPtoLP returns
negative values for the y coordinate, and therefore you should specify yExt as a
positive value. One way to do this is to use the C run- time library function
abs to get the absolute value of pt.y.
If the mapping mode in which you created your metafile is something other than
MM_TEXT, then you probably will know the width and height of the metafile in
logical units. In this case, to calculate values for xExt and yExt you must
first convert the width and height from logical units to device units before
converting to MM_HIMETRIC units. To do this, the hDC that you use for the
calculation must be in the same mapping mode that was used to create the
metafile. If you created the metafile in the MM_ANISOTROPIC or MM_ISOTROPIC
mapping mode, you must also set the window and viewport extents appropriately so
that the scaling factor is correct in the call to LPtoDP.
pt.x = nWidth;
pt.y = nHeight;
// assumes the hDC is in the appropriate mapping mode
LPtoDP(hDC, &pt, 1);
SaveDC(hDC);
SetMapMode(hDC, MM_HIMETRIC);
DPtoLP(hDC, &pt, 1);
RestoreDC(hDC, -1);
The hMF field in the METAFILEPICT structure should contain the handle to a
Windows memory metafile. Because the memory allocated for any object that is
placed on the clipboard is owned by the clipboard, this handle should be a copy
of the metafile that you created. To fill in the hMF member, call the function
CopyMetaFile.
The following function demonstrates the above approach of filling out the
METAFILEPICT structure, and then copies the metafile to the clipboard:
//*************************************************************
//
// CreateClipboardMetaFile()
//
// Purpose: Allocates and fills out a METAFILEPICT struct and
// copies the metafile to the clipboard.
//
//
// Parameters:
//
// HWND hWnd For OpenClipboard().
// HDC hDC For LPtoDP & DPtoLP. The mapping mode
// must match the logical units that
// nWidth and nHeight are specified in.
// int nWidth Width of the metafile in logical units.
// int nHeight Height of the metafile in logical units.
//
//
// Return: (void)
//
//*************************************************************
void CreateClipboardMetaFile(HWND hWnd,
HDC hDC,
HANDLE hMF,
int nWidth,
int nHeight)
{
HANDLE hMem;
LPMETAFILEPICT lpMFP;
POINT pt;
// Allocate memory for the METAFILEPICT struct
hMem = GlobalAlloc(GMEM_MOVEABLE | GMEM_SHARE, sizeof(METAFILEPICT));
lpMFP = (LPMETAFILEPICT)GlobalLock(hMem);
// MM_ANISOTROPIC ensures that it is scalable on playback
lpMFP->mm = MM_ANISOTROPIC;
// Convert the object width and height into MM_HIMETRIC units.
pt.x = nWidth;
pt.y = nHeight;
// First get the width and height into device units.
// This assumes that the hDC is in the mapping mode that
// matches the logical units that nWidth and nHeight are
// specified in. If nWidth and nHeight are already in device
// units, then this step isn't necessary.
LPtoDP(hDC, &pt, 1);
// Temporarily set the mapping mode to MM_HIMETRIC
SaveDC(hDC);
SetMapMode(hDC, MM_HIMETRIC);
DPtoLP(hDC, &pt, 1);
RestoreDC(hDC, -1);
// Because the y-axis is inverted in the MM_HIMETRIC mapping mode,
// DPtoLP returns negative values for the y coordinate.
// Because of this, we should specify yExt as a positive value.
// Also guard against the obscure case that the logical units
// that nWidth was specified in would cause pt.x to be negative.
lpMFP->xExt = abs(pt.x);
lpMFP->yExt = abs(pt.y);
// Fill in the handle to the metafile.
// Make a copy of the metafile because the memory block allocated
// for it will be owned by the clipboard. The memory allocated for the
// METAFILEPICT struct will also be owned by the clipboard.
lpMFP->hMF = CopyMetaFile(hMF, NULL);
GlobalUnlock(hMem);
// Copy the metafile to the clipboard.
OpenClipboard(hWnd);
EmptyClipboard();
SetClipboardData(CF_METAFILEPICT, hMem);
CloseClipboard();
}
Additional query words: 3.10 metafile MM_HIMETRIC METAFILEPICT
======================================================================
Keywords : kbSDKWin16
Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310
Version : WINDOWS:3.1
Issue type : kbinfo
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