Then use the lineTo API to draw a line from the start point to the end point passed in to the lineTo call.
然后使用lineTo API来从这个起始点到传递到这个lineTo调用中的端点之间绘制一条直线。
After drawing both axes, you draw the gridlines along with their labels by evenly spacing them and then drawing the lines using the same combination of moveTo, lineTo, and stroke.