How to create fully transparent window which has not transparent content?

Question

I have tried this:

#include <windows.h>

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch(msg)
    {
        case WM_CLOSE:
            DestroyWindow(hwnd);
        break;

        case WM_DESTROY:
            PostQuitMessage(0);
        break;

        case WM_SIZE:
        case WM_MOVE:
        case WM_PAINT:
        {
            PAINTSTRUCT ps;
            BeginPaint(hwnd, &ps);
            EndPaint(hwnd, &ps);
            return 0;
        }

        case WM_CTLCOLORSTATIC:
        {
            HDC hdc = (HDC) wParam; 
            SetBkMode (hdc, TRANSPARENT);
            return (LRESULT)(GetStockObject(NULL_BRUSH));
        }

        default:
            return DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}

int main()
{
    WNDCLASSEX wc;
    MSG Msg;

    wc.cbSize        = sizeof(WNDCLASSEX);
    wc.style         = 0;
    wc.lpfnWndProc   = WndProc;
    wc.cbClsExtra    = 0;
    wc.cbWndExtra    = 0;
    wc.hInstance     = NULL;
    wc.hIcon         = NULL;
    wc.hCursor       = NULL;
    wc.hbrBackground = (HBRUSH)(GetStockObject(NULL_BRUSH));
    wc.lpszMenuName  = NULL;
    wc.lpszClassName = L"MY CLASS";
    wc.hIconSm       = NULL;

    RegisterClassEx(&wc);

    HWND hwnd = CreateWindowEx(0, L"MY CLASS", NULL, WS_VISIBLE, 0, 0, 640, 480, NULL, NULL, NULL, NULL);
    HWND child = CreateWindowEx(0, L"STATIC", L"Text", WS_VISIBLE | WS_CHILD , 50, 50, 50, 50, hwnd, NULL, NULL, NULL);

    UpdateWindow(hwnd);

    while(GetMessage(&Msg, NULL, 0, 0) > 0)
    {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return 0;
}

It creates window, which looks transparent, because it shows the same as on screen, however after moving window main window background stays the same. I want to ask, where the problem may be.

PS it is just test code, so, please, do not write advices not suited with my question.

Thanks.

EDIT: I want this because I'm going to make some helpers for users who don't know how to do some stuff. Result should be something like regular some program view with come spots marked, what means press here, when here, after that here and etc.

Answer 1

I think you start point should be with taking a look on Layered Windows

http://msdn.microsoft.com/en-us/library/ms997507.aspx

it is most common way for playing with custom shape and (semi)transparent windows.

UPD. There is also old API for making custom shaped windows:

int SetWindowRgn( HWND hWnd, HRGN hRgn, BOOL bRedraw );