通过设置图形模式，在指定的像素行和列写像素。将像素的行和列看成坐标系的横坐标和纵坐标，那么只要知道要画的图形的函数关系就可以画出该图形。-By setting the graphics mode, the pixel at the specified row and column write pixels. The rows and columns of pixels coordinates as abscissa and ordinate, so long as we know to draw the graph can be drawn as a function of the graphic.