C++实现计算机图形学算法，绘制线（数值微分法、中点画线法、Bresenham法），绘制圆（圆心半径画圆、中心点画圆算法）-C++ realization of computer graphics algorithms, rendering line (numerical differential method, the stipple method of lines, Bresenham method), draw the circle (center of a circle radius d