Creating Metafiles to Use with OLE Applications

• Microsoft OLE version 1.0

SUMMARY

A metafile is one of the presentation formats that can be used by an OLE server application. A server application must prepare data in the presentation format under two circumstances:

• When the user copies an object to the clipboard, using the Copy command from the Edit menu
• When the OLE libraries call the GetData method

MORE INFORMATION

METAFILEPICT Structure

When an application creates a metafile to use with the OLE libraries or with the clipboard, all interactions occur through the METAFILEPICT data structure, which is defined as follows:

typedef struct tagMETAFILEPICT {

  int mm;         // Mapping mode
  int xExt, yExt; // Horizontal and vertical size
  HANDLE hMF;     // Handle to the metafile

The mapping mode for the metafile must be MM_ANISOTROPIC, which ensures that the object will scale properly when the client application displays it. However, the OLE libraries store a size for the object that is specified in MM_HIMETRIC units [0.01 millimeter (mm)]. The maximum size of an object is 327.67 mm by 327.67 mm.

The application obtains the handle to the metafile by calling the CreateMetaFile function with NULL as the lpFilename parameter. Doing so creates a memory-based metafile.

Fonts

A server application should use a TrueType font whenever possible in a metafile. This is important because the user can scale the object to many different sizes in the client application and TrueType fonts scale well under a variety of conditions. To specify a TrueType font, set bit 2 (04h) of the lfPitchAndFamily member in the LOGFONT data structure.

Creating the Metafile

The following eleven steps present the procedure to create a metafile compatible with the OLE libraries:

1. Retrieve a metafile device context (DC).

   hMetaDC = CreateMetaFile(NULL);

2. Call the SetWindowOrg function to set the origin to (0, 0).

   SetWindowOrg(hMetaDC, 0, 0);

3. Call the SetWindowExt function specifying the width and the height of the object.

   SetWindowExt(hMetaDC, ObjWidth, ObjHeight);

4. Draw the object in the metafile DC.

   DrawObject(hMetaDC, lpObject); // Application-specific function

                                         // that draws the object into an
                                         // arbitrary DC.
   
   

5. Close the metafile.

   hMF = CloseMetaFile(hMetaDC);

6. Allocate a METAFILEPICT structure from global memory. Because this memory will be shared between applications, the memory must allocated with the GMEM_SHARE flag.

   hMem = GlobalAlloc(GMEM_MOVEABLE | GMEM_SHARE,

                             sizeof(METAFILEPICT));
   
   

7. Lock the memory block to retrieve a pointer to the METAFILEPICT structure (lpMFP).

   lpMFP = (LPMETAFILEPICT)GlobalLock(hMem);

8. Set the mapping mode to MM_ANISOTROPIC.

   lpMFP->mm = MM_ANISOTROPIC;

9. Convert the object width and height into MM_HIMETRIC units. Fill in the METAFILEPICT data structure with the information.

   pt.x = ObjWidth; pt.y = ObjHeight; hDC = GetDC(hWnd); // Borrow a DC from the main window. oldMapMode = SetMapMode(hDC, MM_HIMETRIC); DPtoLP(hDC, &pt, 1); SetMapMode(hDC, oldMapMode); ReleaseDC(hWnd, hDC);

   lpMFP.xExt = pt.x; lpMFP.yExt = pt.y;

10. Put the metafile handle into the METAFILEPICT data structure.

    lpMFP->hMF = hMF;

11. Unlock the memory block and use the handle appropriately.

    GlobalUnlock(hMem);