C++ / MFC, rendering to a local CPaintDC and saving to file

So, as I said in an earlier post I've been trying to write some MFC C++ code to (1) create a CPaintDC, (2) render to it, and (3) save it to file as a BMP or DIB.  And I haven't been able to get this to work, surprisingly.

The code I've cobbled together from doc and samples is below, but for some reason it just outputs a black/null square.  (I should be drawing a green square.)

Can anyone see any problems with this code?

Thanks *very* much for any help.

void CMFCApplication_TestDIBDlg::OnBnClickedButton1()
{
    CPaintDC dc(this);
    CRect rc;
    GetClientRect(rc);
    dc.FillSolidRect(rc, 0x0000FF00);  // aarrggbb ; green

    HBITMAP m_hBmp;
    LPBYTE pBits;

    BITMAPINFO bmi;
    memset(&bmi, 0, sizeof(BITMAPINFO));
    bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bmi.bmiHeader.biWidth = rc.Width();
    bmi.bmiHeader.biHeight = -rc.Height(); // top-down
    bmi.bmiHeader.biPlanes = 1;
    bmi.bmiHeader.biBitCount = 32;
    bmi.bmiHeader.biCompression = BI_RGB;

    m_hBmp = CreateDIBSection(dc, &bmi, DIB_RGB_COLORS, (void**)&pBits, NULL, NULL);

    CImage image;
    image.Attach(m_hBmp);
    image.Save(L"c:\\dum.bmp", Gdiplus::ImageFormatBMP);

    MessageBox(L"Done", L"debug", 0);
}

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