Make isItemViewable handle floating point error.

[tpcstld]

Description

I'm not sure there is an issue for this. I can create one if necessary.

While working on a react-native app, I noticed that some views would never initially appear as visible according to onViewableItemsChanged. From debugging, I isolated the issue to ViewabilityHelper's isItemViewable. https://github.com/Shopify/flash-list/blob/main/src/viewability/ViewabilityHelper.ts#L141

I'm not able to share a video or repro, I'm pretty certain that what I'm seeing is minute differences between pixelsVisible and itemSize. For an example view, I get pixelsVisible = 36.761904761904816 and itemSize = 36.76190476190476. I feel like that these differences are likely caused by floating-errors from prior calculations.

Reviewers’ hat-rack 🎩

• Do you agree with my hypothesis and reasoning?
• Should I alternatively do if (pixelsVisible - itemSize >= -0.001)? i.e. allow pixelsVisible to be greater than itemSize in general?
• Is 0.001 a suitable arbitrary number?

Screenshots or videos (if needed)

Unfortunately I cannot provide this easily. :(

Checklist

• I have added a changelog entry following the Keep a Changelog guidelines.

[tpcstld]

I will work on getting the CLA signed 😔

[tpcstld]

I have signed the CLA!

[github-actions]

CLA: Unexpected error has occurred, please re-run the workflow.

We are sorry for the inconvenience, due to GitHub actions limitations this requires a manual intervention.

There are few ways to do it:

• Create a new pull request with the same changes.
• Push an empty commit to the branch.
• Rebase the branch on top of the latest master might also help.

If the issue persists, please contact the maintainers of this repo.