关于GestureDetector.OnGestureListener的onScroll参数distance问题

关于GestureDetector.OnGestureListener类的onScroll方法参数distanceX和distanceY问题

看到有文章上说onScroll方法中distanceX和distanceY是指“distanceX，是前后两次call的X距离，不是e2与e1的水平距离； 是前后两次call的Y距离，不是e2与e1的垂直距离”

然后怎么也没理解出来这两个参数是什么意思

于是去实践了一下：

以下是谷歌官方API说明：

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public abstract boolean onScroll (MotionEvent e1, MotionEvent e2, float distanceX, float distanceY)

Added in API level 1

Notified when a scroll occurs with the initial on down MotionEvent and the current move MotionEvent. The distance in x and y is also supplied for convenience.

Parameters

e1	The first down motion event that started the   scrolling.
e2	The move motion event that triggered the current onScroll.
distanceX	The distance along the X axis that has been scrolled   since the last call to onScroll. This is NOT the distance between e1 and e2.
distanceY	The distance along the Y axis that has been scrolled   since the last call to onScroll. This is NOT the distance between e1 and e2.

Returns

true if the event is consumed, else false

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“The distance along the X axis that has been scrolled since the last call to onScroll. This is NOT the distance between e1 and e2.”

这句话按我自己翻译出来的意思是“在上一次（最后一次）调用onScroll方法沿着X轴所滑动的距离。不是e1和e2之间的距离”

我的理解是：distanceX是滑动起点和终点的水平距离，而不是起点和终点的直线距离。

写了个例子在LogCat中输出了一下它们的值：

发现

distanceX的值等于e1的X值减去e2的X值，计算结果带正负号。

distanceY的值等于e1的Y值减去e2的Y值，计算结果带正负号。

不知道这理解正不正确，如有错误望指正。