GetWindowDC

GetWindowDC is a Win32 API function that retrieves a handle to a device context (HDC) for an entire window, including the non-client areas such as the title bar, borders, scroll bars, and menus. It is part of the Windows GDI (Graphics Device Interface) and is used when drawing or examining the full visual extent of a window outside just its client area.

When a window's client area is drawn, applications typically use GetDC to obtain a device context for the client region. GetWindowDC, in contrast, provides a device context that encompasses both client and non-client regions of the specified window. This can be useful for tasks that involve manipulating or inspecting non-client elements, but it should be used with care because non-client rendering is handled by the system in many contexts.

The function takes a window handle (HWND) and returns an HDC on success or NULL on failure. If a DC is obtained, it must be released with ReleaseDC when drawing is complete. The DC obtained by GetWindowDC is not intended for long-term painting and may require additional handling when the window is being redrawn or themed.

Best practices advise using GetWindowDC sparingly and avoiding it for normal painting tasks. For client-area painting, BeginPaint/EndPaint within a WM_PAINT handler is recommended. For non-client customization, alternative APIs or mechanisms provided by the system should be considered, as non-client drawing is often managed by the window manager.

See also: GetDC, GetDCEx, ReleaseDC, BeginPaint, EndPaint.