Does CMFCStatusBar::SetPaneIcon supports alpha icon? - c++

Question

My App setup icons for panes in status bar (class CMFCStatusBar). There is only one method for this task - CMFCStatusBar::SetPaneIcon(). But if icon have alpha channel this method loads wrong image (on black background).
I looked into the source code and I saw that CMFCStatusBar uses internal HIMAGELISTs for every panes. All this HIMAGELIST creates with flag ILC_MASK | ILC_COLORDDB, not ILC_COLOR32 or ILC_COLOR24.
This is a bug!
So, is there a way to use the icons with alpha channel in CMFCStatusBar panes?
Example:
HICON hIcon = ::LoadImage(hModule, MAKEINTRESOURCE(nIconID), IMAGE_ICON, 16, 16, LR_DEFAULTCOLOR);
m_StatusBar.SetPaneIcon(m_StatusBar.CommandToIndex(ID_INDICATOR_1), hIcon);

Answer 1

Microsoft developed the CMFC classes (Feature Pack) from the BCG toolkit. If you compare the CMFCStatusBar::SetPaneIcon() method with the BCG method from the same class, you’ll notice a few subtle differences.
BCG defines its method with a flag for alpha blend. The method looks like:
void CBCGPStatusBar::SetPaneIcon (int nIndex, HBITMAP hBmp,
COLORREF clrTransparent, BOOL bUpdate, BOOL bAlphaBlend/* = FALSE*/)
The CMFC equivalent removes the ‘bAlphaBlend’ flag.
Comparing the method code, you’ll see that BCG uses the following code that has been removed from the CMFC version:
DWORD dwFlags = ILC_MASK | ILC_COLORDDB;
if (bAlphaBlend)
{
dwFlags = ILC_COLOR32;
}
pSBP->hImage = ::ImageList_Create (pSBP->cxIcon, pSBP->cyIcon, dwFlags, 1, 0);
I’m not sure why the CMFC version differs so much (Microsoft may have a valid reason), but, I’ve included the BCG version below. I would study the BCG version and possibly create your own ‘SetPaneIcon’ method from that code (at your own risk).
void CBCGPStatusBar::SetPaneIcon (int nIndex, HBITMAP hBmp,
COLORREF clrTransparent, BOOL bUpdate, BOOL bAlphaBlend/* = FALSE*/)
{
ASSERT_VALID(this);
CBCGStatusBarPaneInfo* pSBP = _GetPanePtr(nIndex);
if (pSBP == NULL)
{
ASSERT (FALSE);
return;
}
// Disable animation (if exist):
SetPaneAnimation (nIndex, NULL, 0, FALSE);
if (hBmp == NULL)
{
if (pSBP->hImage != NULL)
{
::ImageList_Destroy (pSBP->hImage);
}
pSBP->hImage = NULL;
if (bUpdate)
{
InvalidatePaneContent (nIndex);
}
return;
}
BITMAP bitmap;
::GetObject (hBmp, sizeof (BITMAP), &bitmap);
if (pSBP->hImage == NULL)
{
pSBP->cxIcon = bitmap.bmWidth;
pSBP->cyIcon = bitmap.bmHeight;
DWORD dwFlags = ILC_MASK | ILC_COLORDDB;
if (bAlphaBlend)
{
dwFlags = ILC_COLOR32;
}
pSBP->hImage = ::ImageList_Create (pSBP->cxIcon, pSBP->cyIcon, dwFlags, 1, 0);
RecalcLayout ();
}
else
{
ASSERT (pSBP->cxIcon == bitmap.bmWidth);
ASSERT (pSBP->cyIcon == bitmap.bmHeight);
::ImageList_Remove (pSBP->hImage, 0);
}
//---------------------------------------------------------
// Because ImageList_AddMasked changes the original bitmap,
// we need to create a copy:
//---------------------------------------------------------
HBITMAP hbmpCopy = (HBITMAP) ::CopyImage (hBmp, IMAGE_BITMAP, 0, 0, 0);
if (bAlphaBlend)
{
::ImageList_Add (pSBP->hImage, hbmpCopy, NULL);
}
else
{
::ImageList_AddMasked (pSBP->hImage, hbmpCopy, clrTransparent);
}
::DeleteObject (hbmpCopy);
if (bUpdate)
{
InvalidatePaneContent (nIndex);
}
}

Answer 2

My solution, based in rrirower code.
CMFCStatusBarPaneInfo* CMyStatusBar::GetPane(int nIndex) const {
if (nIndex == 255 && m_nCount < 255) {
// Special case for the simple pane
for (int i = 0; i < m_nCount; i++)
{
CMFCStatusBarPaneInfo* pSBP = GetPane(i);
ENSURE(pSBP != NULL);
if (pSBP->nStyle & SBPS_STRETCH) {
return pSBP;
}
}
}
if (nIndex < 0 || nIndex >= m_nCount) {
return NULL;
}
if (m_pData == NULL) {
ASSERT(FALSE);
return NULL;
}
return((CMFCStatusBarPaneInfo*)m_pData) + nIndex;
}
void CMyStatusBar::SetPaneIcon(int nIndex, HICON hIcon, BOOL bUpdate /*= TRUE*/)
{
ASSERT_VALID(this);
CMFCStatusBarPaneInfo* pSBP = GetPane(nIndex);
if (pSBP == NULL)
{
ASSERT(FALSE);
return;
}
// Disable animation(if exist):
SetPaneAnimation(nIndex, NULL, 0, FALSE);
if (hIcon == NULL)
{
if (pSBP->hImage != NULL)
{
::ImageList_Destroy(pSBP->hImage);
}
pSBP->hImage = NULL;
if (bUpdate)
{
InvalidatePaneContent(nIndex);
}
return;
}
ICONINFO iconInfo;
::GetIconInfo(hIcon, &iconInfo);
BITMAP bitmap;
::GetObject(iconInfo.hbmColor, sizeof(BITMAP), &bitmap);
::DeleteObject(iconInfo.hbmColor);
::DeleteObject(iconInfo.hbmMask);
if (pSBP->hImage == NULL)
{
pSBP->cxIcon = bitmap.bmWidth;
pSBP->cyIcon = bitmap.bmHeight;
pSBP->hImage = ::ImageList_Create(pSBP->cxIcon, pSBP->cyIcon, ILC_COLOR32 | ILC_MASK, 1, 0);
::ImageList_AddIcon(pSBP->hImage, hIcon);
RecalcLayout();
}
else
{
ASSERT(pSBP->cxIcon == bitmap.bmWidth);
ASSERT(pSBP->cyIcon == bitmap.bmHeight);
::ImageList_ReplaceIcon(pSBP->hImage, 0, hIcon);
}
if (bUpdate)
{
InvalidatePaneContent(nIndex);
}
}