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

[Lexachoc]

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:

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

For scattergl case, it always shows label A:

[camdecoster]

Thanks for the report! I agree that this is a bug. scatter and scattergl break distance ties in different ways. I think that scatter handles this correctly where the trace on top wins. I'll put a quick PR together because it's a one character update.

[Lexachoc]

It seems a bit more complicated than a one character update.

Is this the line you were referring to? I noticed it too:

plotly.js/src/traces/scattergl/hover.js

Line 95 in 0aabc3c

if(dist < minDist) {

But scatter also takes marker size into account when determining hover behavior, together with trace order.

plotly.js/src/traces/scatter/hover.js

Lines 64 to 67 in 0aabc3c

	// scatter points: d.mrc is the calculated marker radius
	// adjust the distance so if you're inside the marker it
	// always will show up regardless of point size, but
	// prioritize smaller points