说明：  基于MFC的openGL编程实例，GDI是通过设备句柄（Device Context以下简称"DC"）来绘图，而OpenGL则需要绘制环境（Rendering Context，以下简称"RC"）。
(A programming example of openGL based on MFC GDI is drawn by Device Context (hereinafter referred to as "DC"), while OpenGL requires Rendering Context (hereinafter referred to as "RC").)