Microsoft-ui-xaml: Scrollbar thumb does not shrink upon overscroll via touchpad or touchscreen

[Poopooracoocoo]

Describe the bug

Scrollbar does not shrink open overscroll via touchpad/touchscreen

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Open Start menu
2. Drag down

Expected behavior

Scrollbar would shrink like pre-conscious scrollbars or like IE

Version Info

| Windows 10 version | Saw the problem? |
| :--------------------------------- | :-------------------- |
| May 2019 Update (18362) | Yes |
| October 2018 Update (17763) | Yes |
| April 2018 Update (17134) | Yes |
| Fall Creators Update (16299) | No |
| Creators Update (15063) | No |
| Anniversary Update (14393) | No |

| Device form factor | Saw the problem? |
| :-------------------- | :------------------- |
| Desktop | Yes |
| Mobile | |
| Xbox | |
| Surface Hub | |
| IoT | |

Additional context

I'm sorry if it's not in the scope of WinUI but I hope you can raise this issue with the people working on Windows just like the issue I submitted earlier on the Start Menu's missing backplate

[jevansaks]

Seems like a reasonable request. It's something we can look into post-WinUI 3.0.

[Poopooracoocoo]

It's still funny to me that the conscious scrollbar rewrite didnt implement this. Its not as funny as the task view and touch keyboard rewrites though as those impact me greatly

[Poopooracoocoo]

I noticed that when auto hiding scrollbars are disabled, all scrollbars will briefly be hidden and then expand.

[DragoCubed]

I've also noticed that when you scroll semi-fast the new scrollbar will be very choppy.

[micahl]

@DragoCubed choppy how?

[Poopooracoocoo]

It's definitely not in sync and a bit behind. Rather hard to explain without a recording. I'm easily able to reproduce it.

[DragoCubed]

@micahl

What happened? What changed with W10 v1803? Were you able to repro the choppiness?

[micahl]

@DragoCubed, dunno. We did introduce the setting to keep scrollbars always visible with v1803. Perhaps something with that change is related to the issue. I haven't noticed any choppiness with the scrollbar on the start menu. I assume that's where you're seeing the choppiness. Any chance you have a video that demonstrates it?

[Poopooracoocoo]

@micahl I remember the choppiness being there before that setting was introduced. By the way, content doesn't always get pushed when hiding scrollbars are disabled. If I record it I'll update this

[Poopooracoocoo]

On scrollbars:

I've disabled auto-hide scrollbars and in XAML Controls Gallery, the NavigationView looks like this: