说明：  四个波形产生例子，一个是自己产生正弦波，一个是自己在垂直坐标轴上画直线，另两个是在垂直坐标轴上画随机线，对于学习怎么画波形来说是挺好的例子，值得学习
(Four waveform generator example, a generated sine wave, one is the vertical axis draw a straight line, the other two draw random lines in the vertical axis, is a good example to learn how to draw the waveform, worth learning)