MFC 中设备环境类的派生层次如下:
CObject
CDC
CClientDC
CPaintDC
CWindowDC
CMateFileDC
1 CDC 类
The CDC class defines a class of device-context objects. The CDC
object provides member functions for working with a device context,
such as a display or printer, as well as members for working with a
display context associated with the client area of a window. Do all
drawing through the member functions of a CDC object. The class
provides member functions for device-context operations, working with
drawing tools, type-safe graphics device interface (GDI) object selection,
and working with colors and palettes.
It also provides member functions for getting and setting drawing
attributes, mapping, working with the viewport, working with the window
extent, converting coordinates, working with regions, clipping, drawing
lines, and drawing simple shapes, ellipses, and polygons.
Member functions are also provided for drawing text, working with fonts,
using printer escapes, scrolling, and playing metafiles.
To use a CDC object, construct it, and then call its member functions
that parallel Windows functions that use device contexts.
For specific uses, the Microsoft Foundation Class Library provides
several classes derived from CDC .
CPaintDC encapsulates calls to BeginPaint and EndPaint. CClientDC
manages a display context associated with a window's client area.
CWindowDC manages a display context associated with an entire
window, including its frame and controls. CMetaFileDC associates a
device context with a metafile.
CDC contains two device contexts, m_hDC and m_hAttribDC, which,
on creation of a CDC object, refer to the same device.
CDC directs all output GDI calls to m_hDC and most attribute GDI calls
to m_hAttribDC. (An example of an attribute call is GetTextColor, while

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