在Windows平台上，应用程序的图形设备接口（graphics device interface，GDI）被抽象为设备上下文（Device Context，DC）。
　在微软基类库MFC中，CDC类是定义设备上下文对象的基类，所有绘图函数都在CDC基类中定义。当需要输出文字或图形时，就需要调用CDC类的成员函数，这些成员函数具备输出文本、绘制图形的功能。
　本节讲解的例程全部在TestView.cpp文件的
void CTestView::OnDraw(CDC* pDC)函数中实现。(In the Microsoft base class library MFC, the CDC class is the base class that defines the device context object, and all the drawing functions are defined in the CDC base class. When you need to output text or graphics, you need to call the CDC class member functions, these member functions with output text, drawing graphics function.
The routines explained in this section are all in the TestView.cpp file
Implementation of void CTestView:: OnDraw (CDC* pDC) function.)