Which tooltip is triggered by superimposed scatter points does not follow comprehensible logic

[tnafele]

Expected behaviour

If a series has several points at the exact same coordinates, the tooltip triggered at these coordinates should always belong to the last point drawn, i.e. the one visible at the top of the stack.

Which tooltip is triggered should be manipulable or at least predictable.

Actual behaviour

The behavior seems random. Sometimes the triggered tooltip belongs to the top point, sometimes to one below.

Live demo with steps to reproduce

https://jsfiddle.net/5fzrvaq9/

Product version

latest (11.4)

Affected browser(s)

any

[bm64]

Hello @tnafele and thank you for reaching out.

The findNearestPointBy property lets you decide whether points are selected based on the x pointer position or both xy (default for scatter series). In the provided demo, the point closest to the pointer is selected as expected. Could you clarify what exactly you don't like about this behaviour?

[tnafele]

Hi @bm64

Thank you for your reply.

The issue comes with superimposed scatter points. I.e. they have exactly the same position (x1, y1) === (x2, y2). We are talking about a stack of points.

If two or more points are overlaid like that, which one is selected?

The behavior should be predictable. In an old version (V4) it was always the upmost point, i.e. the one visible. This is how it should be. With later versions this seems random!

Please see the fiddle here.

The points shown in the graph are always superimposing others. A blue one is on top of red one.

Here (x=1, y=1) the upmost point (blue) is selected hence the tooltip shows it's properties (name = "blue"): This is the expected behavior.

Here (x=1, y=4) the point below (red) is selected hence the tooltip shows it's properties (name = "red"): This is unexpected.

At x=3, y=2 there are four points at the exact same position. Here, the third in the stack is selected (green). This is unexpected.

This shows that the behavior is obviously not predictable.

The user should be able to rely on the fact that when arranging the overlapping points in a specific order, the point at the top will always be selected.

[bm64]

@tnafele, thanks for the detailed explanation!