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Window Display Device Contexts
A window DC enables an application to draw anywhere in a window, including the
nonclient area. Window DCs are typically used by applications that process the WM_NCPAINT and WM_NCACTIVATE messages for windows with custom nonclient areas. Using a window DC is not
recommended for any other purpose.
An application can retrieve a window DC by using the GetWindowDC or GetDCEx function with the DCX_WINDOW option specified. The function retrieves a
window DC from the display DC cache. A window that uses a window DC must release it
after drawing by using the ReleaseDC function as soon as possible. Window DCs are always from the cache; the
CS_OWNDC and CS_CLASSDC class styles do not affect the DC.
When an application retrieves a window DC, Windows sets the device origin to
the upper left corner of the window instead of the upper left corner of the
client area. It also sets the clipping region to include the entire window, not
just the client area. Windows sets the current attribute values of a window DC to
the same default values as a common DC. An application can change the attribute
values, but Windows does not preserve any changes when the DC is released.
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