Scrolling with startRenderingFromBottom is WAY slower
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Description
Description
The only thing I am changing is whether startRenderingFromBottom is false or true. When false, scrolling is fast. When true, scrolling is slow in the sense that I am swiping as fast as I can and the view is just scrolling very slowly. Not janky, just slow. I notice that once I scroll past say a certain item, if I reverse the scroll direction then it's back to really fast while scrolling in that opposite direction. So like, it's only fast in the zone that I have already visited. Once I scroll back to items I haven't seen yet, then it slows right back down.
I never ran into this issue with old arch and flash list v1. I'm guessing that's because logic is now running on main thread which is slowing down scrolling, whereas before the async nature prevented slow scrolling.
Platform
Android
FlashList version: 2.0.3
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Reproduce the issue on Android with FlashList 2.0.3, comparing startRenderingFromBottom set to false and true while scrolling into unseen items. Investigate whether the slower forward scrolling is associated with work on the main thread; done means scrolling speed remains responsive in both directions and the reported behavior no longer occurs.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- react-native, typescript
- Domain
- mobile, performance
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100