How to render CRichEditCtrl on CDC with transparent backgorund ? (MFC)

Question

I need help with rendering CRichEditCtrl content with transparent background on graphical context which is displayed on screen and printed as well. Now I have following code, which is working good except transparency issues:

CRichEditCtrl ctrl; // my CRichEditCtrl
CDC *dc; // - my graphical context

dc->SetBkMode(TRANSPARENT);
dc->DPtoHIMETRIC(&targetSize);
CRect cHiMetricRect( 0, 0, origSize.cx*factor,origSize.cy*factor);
CRect cTwipsRect( 0, 0, (TWIPS_INCH * targetSize.cx + HIMETRIC_INCH / 2) / HIMETRIC_INCH, (TWIPS_INCH * targetSize.cy + HIMETRIC_INCH / 2) / HIMETRIC_INCH);

CMetaFileDC metaFile;
metaFile.CreateEnhanced( dc, NULL, cHiMetricRect, NULL );
metaFile.SetBkMode(TRANSPARENT);
metaFile.SetAttribDC( dc->m_hDC );

FORMATRANGE stFR;
stFR.hdcTarget = stFR.hdc = metaFile.m_hDC; 
stFR.rcPage = stFR.rc = cTwipsRect;
stFR.chrg.cpMin = 0;
stFR.chrg.cpMax = -1;

ctrl.FormatRange( &stFR, TRUE);
ctrl.FormatRange( NULL, TRUE);

HENHMETAFILE hMetaFile = metaFile.CloseEnhanced();

dc->PlayMetaFile(hMetaFile,&cr);
DeleteEnhMetaFile(hMetaFile);

I need to render this text with transparency because there are already things drawn on my DC. I tried to search web for any help about metafiles and transparency but found nothing adequate. I will be thankful for any kind of help.

Answer 1

I'm not very sure about MetaFiles, but I've done something similar with EMFs with straight WinAPI which does work -- call EnumEnhMetaFile instead of PlayMetaFile, like:

BOOL bFirstTime = TRUE;
EnumEnhMetaFile(hDC, m_hEmf, (ENHMFENUMPROC)EmfEnumProc_Play_TranspBackground, &bFirstTime, &rc);

where the EnumProc is defined as

int CALLBACK EmfEnumProc_Play_TranspBackground(HDC hDC, LPHANDLETABLE lpHTable, LPENHMETARECORD lpEMFR, int nObj, LPARAM lpData)
{   BOOL bOK;
    if (lpEMFR->iType == EMR_SETBKMODE)
    {   EMRSETBKMODE* lpEMRBkMode = (EMRSETBKMODE*) lpEMFR;

        if (lpEMRBkMode->iMode == OPAQUE)
        {   EMRSETBKMODE EmrBkMode;
            EmrBkMode.emr.iType = EMR_SETBKMODE;
            EmrBkMode.emr.nSize = (sizeof(EmrBkMode) % 4 == 0 ? sizeof(EmrBkMode) : (((sizeof(EmrBkMode) / 4) + 1) * 4));
            EmrBkMode.iMode = TRANSPARENT;
            bOK = PlayEnhMetaFileRecord(hDC, lpHTable, (LPENHMETARECORD)&EmrBkMode, (UINT)nObj);
            return bOK;
        }
    }

    bOK = PlayEnhMetaFileRecord(hDC, lpHTable, lpEMFR, (UINT)nObj);

    if (lpEMFR->iType == EMR_HEADER)
    {   BOOL* pbFirstTime = (BOOL*)lpData;
        if (*pbFirstTime)
        {   EMRSETBKMODE EmrBkMode;
            EmrBkMode.emr.iType = EMR_SETBKMODE;
            EmrBkMode.emr.nSize = (sizeof(EmrBkMode) % 4 == 0 ? sizeof(EmrBkMode) : (((sizeof(EmrBkMode) / 4) + 1) * 4));
            EmrBkMode.iMode = TRANSPARENT;
            PlayEnhMetaFileRecord(hDC, lpHTable, (LPENHMETARECORD)&EmrBkMode, (UINT)nObj);

            *pbFirstTime = FALSE;
        }
    }

    return bOK;
}

Answer 2

I used EnumEnhMetaFile function:

EnumEnhMetaFile(dc->m_hDC, hMetaFile, myMetafileProc, NULL, rect  );

Then I used callback procedure that retrives each record of metafile:

int metafileProc( HDC hDC, HANDLETABLE *lpHTable, const ENHMETARECORD *lpEMFR, int nObj, LPARAM lpData) {
if ( lpEMFR->iType == EMR_EXTTEXTOUTW ) {
        COLORREF_STRUCT *c = (COLORREF_STRUCT *)&(lastBgColor);
        EMR_EXTTEXTOUTW_STRUCT *s = (EMR_EXTTEXTOUTW_STRUCT *)lpEMFR;
        s->textStruct.options = 0x00;
        if ( bgColorFlag ) {
            bgColorFlag = false;
            renderRect( hDC, s->textStruct.rect, c );
        }
        PlayEnhMetaFileRecord( hDC, lpHTable, lpEMFR, nObj );
} else if ( lpEMFR->iType == EMR_SETBKCOLOR ) {
    BYTE *ptr = (BYTE*)lpEMFR;
    COLORREF temp = *((COLORREF*)(ptr+8));
    if ( temp != 0xFFFFFF ) {
        lastBgColor = temp;
        bgColorFlag = true;
    }
}
return 1;
}

where renderRect( hDC, s->textStruct.rect, c ) is function which draws transparent background in c color. I have to zero options flag for text becouse there was different behaviour in Windows XP and Windows 7 and 8 - after that everything works ok. Thanks for help. Best regards.