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[BUG]: `scatter` and `scattergl` show different hover labels for overlapping data points

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
62/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
javascript
Domain
data-visualization

Research direction

Start with the linked CodePen reproduction and compare hover selection for overlapping points in scatter and scattergl, then trace the scattergl hover entry point and related tests. Done means both trace types select the same trace for coincident points and a regression test covers the reported ordering.

Written by the indexing model from the issue text.

Description

bug P3 size: 1
Description

When two traces have data points at exactly the same position, scatter and scattergl select different traces for the hover label.

In this example, both traces A and B have a point at (1, 0), with A added first and B added second.

With scatter, hovering the point shows the hover label for B (Correct).

With scattergl, hovering the same point shows the hover label for A, even though the traces and their order are otherwise identical.

I would expect scatter and scattergl to behave consistently when resolving overlapping points.

Reproducible example:

https://codepen.io/Lexachoc/pen/ogZWJKe

For scatter case:

Image

When moving even closer to marker center, label A will then show:

Image

For scattergl case, it always shows label A:

Image
Dominant language
JavaScript
Stars
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Forks
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Avg merge
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Merged PRs (30d)
21

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