Printing from a worker thread, how?

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C++

MFC

My app is so compute bound that it can run for on the order of a minute. During that time, it is drawing to the screen, but you cannot stop it. The message pumps have stopped, I presume. I have solved the painting problem but not the printing problem, so I'll give you the gist of painting. I start the worker thread in OnPaint and pass the thread parms the "this" pointer and HWND hwnd. The hwnd comes from GetSafeHwnd(). OnPaint is now done and returns.

I've learned not to use CDC In the worker (painter) thread, I do this:

HDC hdc = GetDC(ps->hwnd);   // ps = pointer to thread parm structure
DrawAll(hdc);     // heavy duty computing here
ReleaseDC(ps->hwnd);
return;

OnPrint() is similar to OnPaint() but is a tad more complicated. The starter thread looks like this:

void CMyView::StartPrinterThread(CDC* pdc, CPrintInfo* pInfo)
{
    PrintParam.pv = (CMyView*)this;
    CMyDoc* pDoc = GetDocument();
    PrintParam.pInfo = pInfo;

    pDoc->m_bStopThread = FALSE; // so can stop with a mouse click
    ResetEvent(pDoc->m_hevPrinter);
    AfxBeginThread(PrinterThread,&PrintParam);
    WaitForSingleObject(pDoc->m_hevPrinter, INFINITE);
}

static UINT PrinterThread(LPVOID pParam)
{
    CPrintInfo* pInfo;
    HDC hdc;
    RECT rcl;
    POINT Org;
    PRINTPARMSTRUCT* ps = (PRINTPARMSTRUCT*)pParam;
    // some app specific stuff
    CMyDoc* pDoc = ps->pv->GetDocument();
    pInfo = ps->pInfo;
    hdc = pInfo->m_pPD->m_pd.hDC;
    SetMapMode(hdc, MM_LOENGLISH);
    rcl = pInfo->m_rectDraw;
    ...
    SetEvent(pDoc->m_hevPrinter);  // starter thread going
    DrawAll(hdc);     // heavy duty computing here
    return 0;
}

My app actually runs as expected but for a small detail. The print preview page and the printed page are blank. I hope it is something small that I am missing.

Tom Stokes