一个圆形的表盘，没用库函数，全是自己写的。直线用的brensenham算法，曲线用的坐标对称，编程的时候挺费劲的。(A circular dial, not using the library function, is all written by himself. The brensenham algorithm used in the straight line, the coordinate symmetry of the curve, is difficult when programm