When dragging the scroll bar, reported direction ist always "right" and stays "right" afterwards

[odysseuscm]

Hello 👋

Describe the bug
I use the on "scroll" event to determine the scroll direction. When scrolling with the mouse wheel the direction is correctly reported as "up" and "down". When scrolling by dragging the scroll bar, the direction is always reported as "right" and from now on stays "right" whichever way you scroll. Even if you scroll by mouse wheel again.

To Reproduce
I built a test case here: https://kunden.cmcm.info/ls-direction-bug/index.html
Once you drag the scroll bar, the reported direction is always "right".

Expected behavior
Scroll direction should be reported correctly whatever way you scroll

Desktop (please complete the following information):
confirmed for Chrome 95 and Firefox 93

[odysseuscm]

It might be fixed by changing line 2400:

FROM:

if (this.instance.delta.x > this.instance.scroll.x) {
   if (this.instance.direction !== 'right') {
      this.instance.direction = 'right';
   }
}

TO:

else if (this.instance.delta.x > this.instance.scroll.x) {
   if (this.instance.direction !== 'right') {
      this.instance.direction = 'right';
   }
}

But I'm not sure if that causes problems with detection of horizontal scroll direction.

[odysseuscm]

I made another test case with horizontal scrolling and it worked fine with my fix. So I'm proposing this change.
Here are the tests with the small fix applied:
https://kunden.cmcm.info/ls-direction-bug/fixed-vertical.html
https://kunden.cmcm.info/ls-direction-bug/fixed-horizontal.html

Another way would be to limit the check of delta.y / scroll.y respectively delta.x / scroll.x depending on what scroll direction is set upon instantiation.

Of course the real question is why dragging the scroll bar reports delta.x / scroll.x difference at all when scrolling is set to vertical. But I'd have to first understand the library better, to find the cause.

[odysseuscm]

I took a deeper look. The real problem is here:

if (this.isDraggingScrollbar) {
  requestAnimationFrame(function () {
    var x = (e.clientX - _this5.scrollbarBCR.left) * 100 / _this5.scrollbarWidth * _this5.instance.limit.x / 100;
    var y = (e.clientY - _this5.scrollbarBCR.top) * 100 / _this5.scrollbarHeight * _this5.instance.limit.y / 100;

    if (y > 0 && y < _this5.instance.limit.y) {
      _this5.instance.delta.y = y;
    }

    if (x > 0 && x < _this5.instance.limit.x) {
      _this5.instance.delta.x = x;
    }
  });

x is always smaller than _this5.instance.limit.x when vertical scrolling is used.

Everywhere else horizontal values are only processed when this.direction == 'horizontal', so I guess the correct fix would look like this - which might even be the tiniest bit more performant:

if (this.isDraggingScrollbar) {
    requestAnimationFrame(function () {
    if (_this5.direction == 'horizontal')
    {
      var x = (e.clientX - _this5.scrollbarBCR.left) * 100 / _this5.scrollbarWidth * _this5.instance.limit.x / 100;
      if (x > 0 && x < _this5.instance.limit.x) {
        _this5.instance.delta.x = x;
      }
    }
    else
    {
      var y = (e.clientY - _this5.scrollbarBCR.top) * 100 / _this5.scrollbarHeight * _this5.instance.limit.y / 100;
      if (y > 0 && y < _this5.instance.limit.y) {
        _this5.instance.delta.y = y;
      }
    }
});

[xavierfoucrier]

Hello @Jerek0,

Just discovered this bug, and can confirm it's always the case.
Thanks for fixing this as soon as possible 😉

[odysseuscm]

I posted a patch 1 year ago. #364
I don't know why it was never used - or at least commented on ...

[xavierfoucrier]

@odysseuscm I will have a look 😉

[xavierfoucrier]

@odysseuscm @Jerek0 I can confirm, the patch fix the issue 🎉 , would be nice to merge!

[RafaelKr]

@Jerek0 would be nice if the fix could be merged and published.