What parameters are valid to be together to create an HWND? - model-view-controller

Question

I'm trying to create a window using CWnd::CreateEx(). Unfortunately, I can't seem to get the parameters correct to get it to generate a HWND (function always returns FALSE).
class COverlay : public CWnd
{
public:
COverlay();
DECLARE_MESSAGE_MAP()
};
BEGIN_MESSAGE_MAP(COverlay, CWnd)
END_MESSAGE_MAP()
COverlay::COverlay()
{
}
class CMyView : CView
{
public:
CMyView() {}
int OnCreate(LPCREATESTRUCT lpCreateStruct);
DECLARE_MESSAGE_MAP()
};
BEGIN_MESSAGE_MAP(CMyView, CView)
ON_WM_CREATE()
END_MESSAGE_MAP()
int CMyView::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
if (CView::OnCreate(lpCreateStruct) == -1)
return -1;
m_overlay.CreateEx(WS_EX_COMPOSITED | WS_EX_LAYERED | WS_EX_TRANSPARENT
, _T("Static"), _T(""), WS_VISIBLE | WS_CHILD, CRect(), this, -1);
return 0;
}
I'm trying to create a click through window that overlays the CMyView. In this way I can paint over the view via the overlay and not get flickering as the OS should handle the double buffering and I will only have to deal with the view implementation in a minimal fashion. I will also have an ON_WM_SIZE hander to deal with resizing the overlay to the extents of the view.
What am I doing wrong?
Is there an easier way to do what I am trying to do?

Answer 1

WS_POPUP flag is required to create window with transparency level:
static CString className = AfxRegisterWndClass(0);
DWORD style = WS_CAPTION | WS_SYSMENU | WS_POPUP;
DWORD styleEx = WS_EX_LAYERED;// | WS_EX_TRANSPARENT;
if (!m_overlay.CreateEx(styleEx, className, 0, style, CRect(), this, 0))
{
//error...
return;
}
m_overlay.SetLayeredWindowAttributes(0, 255 * 50 / 100, LWA_ALPHA);
m_overlay.SetWindowPos(0, 0, 0, 400, 300, SWP_SHOWWINDOW | SWP_NOACTIVATE);
Or to change the transparency color:
COLORREF transparentColor = RGB(255, 0, 0);
...
m_overlay.SetLayeredWindowAttributes(transparentColor, 0, LWA_COLORKEY);
void COverlay::OnPaint()
{
CPaintDC dc(this);
CRect rc;
GetClientRect(&rc);
dc.FillSolidRect(rc, transparentColor);
//opaque drawings...
dc.TextOut(0, 0, L"Test...");
}
Note, WS_EX_TRANSPARENT is commented out because that only affects mouse clicks, otherwise it doesn't change the appearance. You can add that flag back in.
This window is popup so it doesn't move when you move the frame window or child window. You would have to override frame and child frame window's OnWindowPosChanged to move it manually to sync with View window.