CImageList and CComboBoxEx limited to 16 transparent icons - c++

Question

It seems that there is a limitation to 16 transparent icons you can use in a CComboBoxEx. I have the following pseudo code:
m_ImageList.Create(16,16,ILC_COLOR32,TF_COUNT,1);
for (int nImage = 0; nImage < TF_COUNT; nImage++)
{
m_ImageList.Add(phIcons[nImage]);
DestroyIcon(phIcons[nImage]);
}
m_cmbAction.SetImageList(&m_ImageList);
The first 16 icons are OK - the following ones all have a black background instead of the transparency. The same code and Image list associated to a CTreeCtrl or a CListCtrl works beautifully. Any ideas?
EDIT: I am using Visual Studio 2013

Answer 1

Author posted his code in a ZIP file:
m_ImageList.Create(16, 16, ILC_COLOR32, TF_COUNT, 1);
for (int nIcon=0; nIcon < TF_COUNT; nIcon++)
{
m_ImageList.Add(m_hIcon);
}
m_ComboBox.SetImageList(&m_ImageList);
COMBOBOXEXITEM cbi;
cbi.mask = CBEIF_IMAGE | CBEIF_INDENT | CBEIF_OVERLAY |
CBEIF_SELECTEDIMAGE | CBEIF_TEXT | CBEIF_LPARAM;
int nItemCount = 0;
for (int nText = 0; nText < TF_COUNT; nText++)
{
CString strItem;
strItem.Format(_T("Item %d"),nText);
cbi.iItem = nItemCount;
cbi.pszText = (LPTSTR)(LPCTSTR)strItem;
cbi.cchTextMax = strItem.GetLength();
cbi.iImage = nText;
cbi.iSelectedImage = nText;
cbi.iOverlay = nText;
cbi.iIndent = 0;
cbi.lParam = nText;
m_ComboBox.InsertItem(&cbi);
nItemCount++;
}
In this code, the error is CBEIF_OVERLAY and cbi.iOverlay = nText. Overlay image is an image drawn transparently over another image (this way, you can combine two icons). In the author's code, that is obviously not the intent.
Finally, image lists allow only up to 15 overlay icons. That explains the magic 16.

Answer 2

Solution 1
If you want to use transparency, you need to create image list with a mask:
m_ImageList.Create(16, 16, ILC_COLOR32 | ILC_MASK, TF_COUNT, 1)
Solution 2
Another (worse) approach is to set the desired background color (after creating the imagelist, but before adding the icons):
m_ImageList.SetBkColor(RGB(0xFF, 0xFF, 0xFF))
The problem about the background color is that you will have to figure which background color to use.
The magic number of 16
I don't think your problem is about CComboBoxEx somehow having problems with the number 16. Instead, I think your icons are a bit different, for example some truly 32-bit, and some in other format. You can test it like that:
m_ImageList.Create(16,16,ILC_COLOR32,TF_COUNT,1);
for (int nImage = 0; nImage < TF_COUNT; nImage++)
{
m_ImageList.Add(phIcons[0]);
}
m_cmbAction.SetImageList(&m_ImageList);
This code adds the same icon multiple times. I bet you won't have any issues with that. Now, you can also try this:
m_ImageList.Create(16,16,ILC_COLOR32,TF_COUNT,1);
for (int nImage = 0; nImage < TF_COUNT; nImage++)
{
m_ImageList.Add(phIcons[16]);
}
m_cmbAction.SetImageList(&m_ImageList);
And you will likely have all icons wrong.
Update 1
I do not have any issues with 16+ transparent icons on my Win8.1, so it's time to suspect that third-party software or your own code is the root of the problem. You need to prepare a minimal example of the code still containing the problem, then try it on another computer. It will be best to try on a virtual machine (you can download prebuilt one here) to reduce all possible risks of whatever software you have installed on many machines at once. If your minimal example still shows the problem on virtual machine, zip it and share with us.