Question

I just started to learn MFC. I need to draw a circle. If I use OnPaint() it works. What should i do that it will draw on background ? Is this the proper function or should I change it?

void Cvaja5Dlg::OnRButtonDown(UINT nFlags, CPoint point)
{
    CPaintDC dc(this);
    dc.Ellipse(0,0,500,500);
    CDialogEx::OnRButtonDown(nFlags, point);
}

Answer 1

No, Windows painting works different way. It’s quite asynchronous.

1. CPaintDC shall be used only inside WM_PAINT handler as it performs BeginPaint()/EndPaint() calls.
2. All drawing usually shall be performed in overrided CWnd::OnPaint()/CView::OnDraw() method.
3. On user input (e.g. right mouse button down) your handler shall change state of your class, e.g. set some bool flag isRightButtonDown and call Invalidate() to initiate asynchronous repainting of window. To enforce synch repainting you could use UpdateWindow() or RedrawWindow() right after invalidating.