plotly / plotly/plotly.js

[BUG]: scattergl hover freezes with more than 100.000 points all with different x but same y

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bug P2 size: 3
Dominant language
JavaScript
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Description

Description

In scattergl, when you have more than 100.000 points the scattergl freezes when trying to hover, more informations in the steps to reproduce.

Steps to reproduce

In version 4.0.0
Create a scattergl with 100.000 points with x just the index of the point and y all the same.
you can use this snipper

const n = 100000;

Plotly.newPlot('graph', [{
  type: 'scattergl',
  mode: 'markers',
  x0: 0,
  dx: 1,
  y: Array(n).fill(0)
}]);

The default hovermode will be ok, no need to change it.
Try hovering on the point: the app freezes immediately.
Staying in the horizontal line of the points will make it look a little slow but normal, but when you exit from the line it freezes again.
Try removing one point (99.999 points): the freeze is gone.

Notes

Probably related to #6792 and #5790 but can't confirm if it's completely the same, this is more specific.
It is probably due to to the collapsation of the algorithm that comes in in a scattergl when there are TOO_MANY_POINTS (exactly 100.000).

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the issue with the provided scattergl JavaScript snippet in Plotly.js 4.0.0, comparing hover behavior at 100,000 and 99,999 points. Trace the scattergl hover path and the TOO_MANY_POINTS handling mentioned in the report, using issues #6792 and #5790 for context. Done means hovering no longer freezes or becomes abnormally slow for the reported data.

Written by the indexing model from the issue text.

Assessment

Tech stack
javascript
Domain
data-visualization
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Active
Clarity
Mostly clear
Newbie friendliness
68/100

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