Some issues with Virtual Scroller

[assuntad23]

Describe the bug
This is a list of the issues I found when playing with the Virtual Scroller. I created a history with a dataset of 1008 items to test this with.

Galaxy Version and/or server at which you observed the bug
Galaxy Version: 21.09/dev

1. Double scroll bar makes scrolling confusing.

• It's hard to tell where you are in the history
• Larger bar jumps around and changes size a bit.
• What is the purpose of the large bar?
• Should they be next to eachother instead of on top of eachother?

2. When scrolling though history with mouse scroller

• Smoothly scrolls for about three long "pulls", then stops and jumps to a seemingly random place in the history (at one point it was 500 datasets lower, at another time it was 800 datasets away)
• After about 300 datasets pass by or so, the history pauses on loading content and you are scrolling through a grey box until it catches up.

3. Top & Bottom of list Oddities

• When at the top, if waiting for a job to run, you must scroll up to see it. The history does not expand to cover the new job in the queue
• When all the way at the bottom, it is possible to show just one dataset, and a whole grey box, even if you have a bunch of datasets. This seems weird.

To Reproduce
Steps to reproduce the behavior:

1. Create a longer history
2. Using the new history, try to scroll up and down fast
3. Try to find a specific place in the history, like a midway point
4. Scroll all the way to the bottom
5. Scroll all the way to the top
6. Add a job to the queue

Expected behavior
The scrolling should behave more consistently and should be easier to navigate through the history. Ease of use for new users is important too.

Screenshots
Here's a video of me playing around with it a bit. It shows some of the odd behaviors.
https://user-images.githubusercontent.com/26912553/133289648-b827244f-478d-424f-940b-1e1a70203384.mp4

** Vue Virtual Scroller Swap **

simplescreenrecorder-2021-09-20_21.17.16.mp4

[jdavcs]

I've observed most of the issues listed here on a smaller sample size (n=100) in Chrome.

[assuntad23]

I created a little powerpoint with some of my findings and my suggestions for moving forward:

https://docs.google.com/presentation/d/1UTDKzRi-McxkHExQ9EBBobczIVg5gUcC0KbHbuH4mVw/edit?usp=sharing

[bgruening]

Thanks @assuntad23.

Would an infinite scroller work, when we add a "jumping" interface to it? Let's say you have 1000 datasets, type in 100 and jump to 100? Would in this case the entire history be loaded, or can we jump to 100 and scroll until 1 without having 1000-900 in the cache?

[assuntad23]

@bgruening I'm not sure, but I'm leaning towards no. There is potential for it to work, but I wonder if it would mess up the order of the whole history to do so. Also, I've never seen anything like that "in the wild".

I think it could is definitely possible with a FOSS Virtual Scroller, but the requirements for those seem to be incompatible with the ContentProvider, afaik, because they expect the whole list of objects upfront.

[dannon]

Closing this as resolved since we've ditched that virtual scroller. Thanks for all the diagnosis and work here @assuntad23.