Grid: scrollToItem / scrollToIndex _softly_

[enver-haase]

Describe your motivation

Soft-scrolling helps understand the transition from showing the old to showing the new item of interest.

Describe the solution you'd like

I would like to see the grid soft-scrolling to the new item, at least when @Push is enabled.

Describe alternatives you've considered

Other CSS fade-in animations can be imagined.

Additional context

Please see https://github.com/enver-haase/monarch -- an AI-coded soft scroll is implemented there and the intended effect can be see there.

[rolfsmeds]

This is probably tricky to get working reliably with virtualization, and especially in TreeGrid.
We'll have a look at the prototype and assess how reliable it can be expected to be.

[tomivirkki]

I tested the provided example in the linked repository. The implementation uses a custom JavaScript animation that directly manipulates table.scrollTop. This works in this specific case because:

• The grid only contains 7 items
• All items have the same height
• The animation scrolls between known fixed positions

With this setup, there isn't any deviation between the scroll position and the rendered position of elements, so the smooth scrolling appears to work.

I also experimented with using this.scrollTarget.scrollTo({ top, behavior: 'smooth' }); directly in the virtualizer's scroll position setter. This similarly works with a limited set of items that all have the same height, but the behavior becomes flaky as soon as:

• Item heights vary OR
• The number of items increases enough

The underlying issue is that iron-list, which we use as our virtual scrolling engine, doesn't have support for smooth scrolling to an index. Reliably supporting it would likely require significant refactoring of the virtualization logic to be "animation-aware".

[rolfsmeds]

Then it looks like we need to postpone this idea until we replace iron-list with another virtualizer sometime in the distant future.