Redrawing window blank

I am amking a etch -e-sketch program and want to redraw the window blank when WM_MOVE is called. I read of a function in the windows GDI called RedrawWindow(), would that do it?

Why not use FillRect?

Code:

RECT rcClient;
GetClientRect(hwnd,&rcClient);
HDC hdc=GetDC(hwnd);
FillRect(hdc,&rcClient,(HBRUSH)GetStockObject(BLACK_BRUSH));
ReleaseDC(hwnd,hdc);

Of course if you don't want to fill the entire client area just define the size/location of your custom RECT yourself instead of using GetClientRect.