Painting Ownerdrawn CStatic with Calculated HRGN - visual-c++

Question

I have a class which inherits from CStatic, which is owner drawn and calculates the region the window should have using SetWindowRgn.
In my DrawItem override I attempt to use FillRgn passing in the same region as was calculated but the method returns FALSE. The Documentation says
Return Value: Nonzero if the function is successful; otherwise 0.
But when I GetLastError the message is "The operation completed successfully".
The window's region is definitely getting the set fine as I have managed to receive WM_LBUTTONUP messages.
Here is my class:
.h file
class Country : public CStatic
{
DECLARE_DYNAMIC(Country)
public:
Country(HBITMAP hBm, CPoint point);
virtual ~Country();
protected:
DECLARE_MESSAGE_MAP()
CPoint m_point;
HBITMAP m_hBm;
BITMAP m_bm;
HDC m_dcBm;
HRGN m_hRgn;
void CreateWindowRgn();
public:
void CreateCountryWindow(CWnd * pParent);
afx_msg void OnLButtonUp(UINT nFlags, CPoint point);
virtual void DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct);
};
.cpp
void Country::DrawItem(LPDRAWITEMSTRUCT lpDrawItemStruct)
{
CDC *pDC = CDC::FromHandle(lpDrawItemStruct->hDC);
CRgn * clientRgn = CRgn::FromHandle(m_hRgn);
CBrush blackBrush(RGB(0,0,0));
if(!(pDC->FillRgn(clientRgn, &blackBrush)))
{
AfxMessageBox(GetLastErrorMessage());
}
}
void Country::CreateCountryWindow(CWnd * pParent)
{
if(Create(
_T(""),
WS_CHILD | WS_VISIBLE | SS_NOTIFY | SS_OWNERDRAW,
CRect(m_point.x, QUESTION_PANEL_HEIGHT + m_point.y, m_bm.bmWidth, m_bm.bmHeight),
pParent))
{
ShowWindow(SW_SHOW);
CreateWindowRgn();
}
}
void Country::CreateWindowRgn()
{
HRGN hTmpRgn;
m_hRgn = CreateRectRgn(0,0,m_bm.bmWidth, m_bm.bmHeight);
for(int i = 0; i < m_bm.bmWidth; i++)
{
for(int j = 0; j < m_bm.bmHeight; j++)
{
COLORREF c = GetPixel(m_dcBm,i,j);
if(GetRValue(c) < 10 && GetGValue(c) < 10 && GetBValue(c) < 10)
{
hTmpRgn = CreateRectRgn(i, j, i+1, j+1);
CombineRgn(m_hRgn, m_hRgn, hTmpRgn, RGN_XOR);
DeleteObject(hTmpRgn);
}
}
}
SetWindowRgn(m_hRgn, TRUE);
}
void Country::OnLButtonUp(UINT nFlags, CPoint point)
{
AfxMessageBox(_T("Hello World"));
CStatic::OnLButtonUp(nFlags, point);
}

Answer 1

As with most MFC problems the answer lies in the documentation:
The system does not make a copy of the region. Thus, do not make
further function calls with this region handle.
Documentation