How to save an Icon to file from an HICON

I thought this would be pretty simple, but it turns out to be quite complicated.

The problem in more detail is this.

Assume that you have only an HICON (which was passed to your function) and wish to write an .ico file (file containing an ICON resource formatted according to the spec)

I am having terrible trouble getting enough information about the Icon to be able to populate the appropriate structures embedded in the resource.


Particularly I have been unable to get GetDIBits to return sensible data

here is a relevant code snippet.


Func( HICON hIconLarge, hIconSmall)
{
ICONINFO iiLarge, iiSmall;

CBitmap oBMLargeColor, oBMLargeMask, oBMSmallColor, oBMSmallMask;
BITMAP bmLargeColor, bmLargeMask, bmSmallColor, bmSmallMask;
BITMAPINFO bmiLargeColor, bmiLargeMask, bmiSmallColor, bmiSmallMask;


// If lpvBits is NULL, GetDIBits examines the first member of the first structure pointed to by lpbi.
// This member must specify the size, in bytes, of a BITMAPCOREHEADER or a BITMAPINFOHEADER structure.
// The function uses the specified size to determine how the remaining members should be initialized.

// If lpvBits is NULL and the bit count member of BITMAPINFO is initialized to zero,
// GetDIBits fills in a BITMAPINFOHEADER structure or BITMAPCOREHEADER without the color table.
// This technique can be used to query bitmap attributes.


// we want a BITMAPINFOHEADER type
bmiLargeColor.bmiHeader.biSize = bmiLargeMask.bmiHeader.biSize = \
bmiSmallColor.bmiHeader.biSize = bmiSmallMask.bmiHeader.biSize = sizeof(BITMAPV4HEADER);

// we want the color table
bmiLargeColor.bmiHeader.biBitCount = bmiLargeMask.bmiHeader.biBitCount = \
bmiSmallColor.bmiHeader.biBitCount = bmiSmallMask.bmiHeader.biBitCount = 1;



     
     GetIconInfo(hIconLarge, &iiLarge);
     GetIconInfo(hIconSmall, &iiSmall);


     oBMLargeColor.Attach(iiLarge.hbmColor);
     oBMLargeMask.Attach(iiLarge.hbmMask);
     oBMSmallColor.Attach(iiSmall.hbmColor);
     oBMSmallMask.Attach(iiSmall.hbmMask);

     oBMLargeColor.GetBitmap(&bmLargeColor);
     oBMLargeMask.GetBitmap(&bmLargeMask);
     oBMSmallColor.GetBitmap(&bmSmallColor);
     oBMSmallMask.GetBitmap(&bmSmallMask);


     CDC* pDC = GetWindowDC();
     HDC hDC = pDC->m_hDC;
     if( 0 == GetDIBits(hDC, iiLarge.hbmColor, bmLargeColor.bmHeight-1, 0, NULL, &bmiLargeColor, DIB_RGB_COLORS) )
          ShowLastError();
     GetDIBits(hDC, iiLarge.hbmMask, bmLargeMask.bmHeight-1, 0, NULL, &bmiLargeMask, DIB_RGB_COLORS);
     GetDIBits(hDC, iiSmall.hbmColor, bmSmallColor.bmHeight-1, 0, NULL, &bmiSmallColor, DIB_RGB_COLORS);
     GetDIBits(hDC, iiSmall.hbmMask, bmSmallMask.bmHeight-1, 0, NULL, &bmiSmallMask, DIB_RGB_COLORS);



     ReleaseDC(pDC);
     oBMLargeColor.Detach();
     oBMLargeMask.Detach();
     oBMSmallColor.Detach();
     oBMSmallMask.Detach();

     DeleteObject(iiLarge.hbmColor);
     DeleteObject(iiLarge.hbmMask);
     DeleteObject(iiSmall.hbmColor);
     DeleteObject(iiSmall.hbmMask);

}