Then use the lineTo API to draw a line from the start pointto 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。
2
P1 If we have a curve c, from a point p0 to a point p1 then the line integral for work depends only on the end points and not on the actual path we chose.
A sawtooth wave rises (or falls) in a straight line from a starting pointto an ending point, at which time it instantaneously jumps back to the starting value.