GetDC: The GetDC() function retrieves a handle to a display device context for the
client area of a specified window or for the entire screen. You can use the
returned handle in subsequent GDI functions to draw in the device context.
HDC GetDC(
HWND hWnd // handle to a window
);
GetWindowDC: The GetWindowDC() function
retrieves the device context (DC) for the entire window, including title bar,
menus, and scroll bars. A window device context permits painting anywhere in a
window, because the origin of the device context is the upper-left corner of
the window instead of the client area. GetWindowDC assigns default attributes
to the window device context each time it retrieves the device context.
Previous attributes are lost.
HDC GetWindowDC(
HWND hWnd // handle of window
);