实现四个功能：一、图和图素1．　　定义屏幕坐标2．　　在屏幕中心作下列图素：点 • ； 小方块 ■ ；大方块 ■ ； 圆点 ● 。以上述图素画线二、3．　　用DDA法画线段；4．　　用DDA法画圆。三、已知如图所示的多面体，其各棱边长均相等。要求1．　　用步进法（即+1比较法）编写AB线段生成程序；2．　　用法线法编写消隐程序；3．　　编写让多面体绕其中心轴线旋转30o、45o、60o的程序四.在三的基础上自动绘制各棱边，自由旋转任意角度-realization of the four functions : 1, maps and map-1. Two definition screen coordinates. In the center of the screen-map for the following : Point # 8226; ; small chunks; large chunks; dots. The above map-line drawing two, three. DDA law with painting segment; 4. With DDA Act Circle. 3, as shown in the figure known polyhedron, its edge longer being equal. Requirements 1. Walking France (a comparison) prepared AB segment generated procedures; 2. Usage prepared blanking line method; 3. To prepare for polyhedron around its central axis rotation 30o, 45o, 60o procedures 4. The three on the basis of automatic drawing the edge, the Liberal arbitrary rotation angle