HMONITOR and the Device Context  Each physical display is
represented by a monitor handle of type HMONITOR. A valid
HMONITOR is guaranteed to be non-NULL. A physical display has
the same HMONITOR as long as it is part of the desktop. When a
WM_DISPLAYCHANGE message is sent, any monitor may be removed
from the desktop and thus its HMONITOR becomes invalid or has
its settings changed. Therefore, an application should check
whether all HMONITORS are valid when this message is sent.  Any
function that returns a display device context (DC) normally
returns a DC for the primary monitor. To obtain the DC for
another monitor, use the EnumDisplayMonitors function. Or, you
can use the device name from the GetMonitorInfo function to
create a DC with CreateDC. However, if the function, such as
GetWindowDC or BeginPaint, gets a DC for a window that spans
more than one display, the DC will also span the two displays.
Build date: 6/12/2013  Community Additions  © 2014 Microsoft.
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