PRB: MetaFile Displays Incorrectly in Print Preview

   SetMapMode
   SetWindowExt, ScaleWindowExt
   SetViewportExt, ScaleViewportExt
   SetViewportOrg, OffsetViewportOrg
				

MORE INFORMATION

The enumeration callback procedure should handle the above functions by calling the (virtual) CDC version of the function while passing everything else to PlayMetaFileRecord(). This allows CPreviewDC to keep the output DC and the attribute DC correctly synchronized with respect to mapping mode. For example:

Sample Code

   int CALLBACK __export EnumMFProc(HDC hdc,
                                    HANDLETABLE FAR *lpht,
                                    METARECORD  FAR *lpmr,
                                    int cObj,
                                    LPARAM lParam)
   {
     // lParam is available for passing application-specific data to the
     // enum proc (via the last parameter to EnumMetaFile). Let's make
     // things easier by passing in a pointer to the CDC object.
   
     CDC *pDC = (CDC *)lParam;
   
     switch(lpmr->rdFunction)
       {
       // SetWindowExt and SetMapMode are the most important ones to
       // look for.
   
       case META_SETWINDOWEXT:
           pDC->SetWindowExt(lpmr->rdParm[1], lpmr->rdParm[0]);
           break;
   
       case META_SETMAPMODE:
           pDC->SetMapMode(lpmr->rdParm[0]);
           break;
   
       case META_SETVIEWPORTEXT:
           pDC->SetViewportExt(lpmr->rdParm[1], lpmr->rdParm[0]);
           break;
   
       case META_SETVIEWPORTORG:
           pDC->SetViewportOrg(lpmr->rdParm[1], lpmr->rdParm[0]);
           break;
   
       // Add cases for the others if desired...
   
       default:
           PlayMetaFileRecord(hdc, lpht, lpmr, cObj);
       }
     return 1;
   }
				

In addition to the functions listed above, there are other functions that will not affect the appearance of the metafile in the Print Preview window, but may affect the synchronization of the output and attribute DCs used by CPreviewDC. This can affect subsequent drawing. Consider that the metafile may select different fonts and other objects into the output DC, may change the foreground/background colors, the text alignment flags, and so forth.

Also, it is common for applications to set a different mapping mode before playing a metafile (depending on the metafile) and this mapping mode may conflict with the mapping mode used by the rest of the view class.

For these reasons, if any drawing will take place after playing the metafile (including playing another metafile, or even the same metafile again), the DC must be restored to the state it was in prior to playing the metafile. This can be accomplished by using SaveDC/RestoreDC, as in the following example:

   pDC->SaveDC();                     // Save current state of DC
   pDC->SetMapMode(MM_ANISOTROPIC);   // Scalable metafile
   pDC->SetViewportExt(xExt, yExt);   // Size of picture
   pDC->SetViewportOrg(x, y);         // Location of picture

   ::EnumMetaFile(pDC->GetSafeHdc(), hmf, EnumMFProc, (LPARAM)(LPSTR)pDC);

   pDC->RestoreDC(-1);                // Restore to previous saved state
                                      // Continue with other drawing...