Add an option to set the opacity of markers in the legend

[subwaymatch]

Can you kindly consider adding an option to set the opacity of legend markers? Currently, the opacities of the legend's markers are tied to the opacity values of the traces.

Plotly Version
plotly.js v2.35.2

Some scatter plots use a very low opacity (<0.10) to display the concentration of overlapping data points.

👇 This can result in imperceptible marker colors in the legend, as shown below:

👇 Feature request: add an option to set the legend marker opacity

I used a workaround to manually set the opacity of the scatterpts class using CSS.

/* current workaround */
.legendpoints .scatterpts {
  opacity: 1 !important;
}

👇 CodePen for Testing

Related posts:

• Issue: px.scatter_geo opacity changes markers opacity and legend items opacity. Is there a way to change one but not the other?
• Legend marker opacity and spacing
• Configuring the alpha (opacity, transparency) for the items in legend of scatter plot of plotly

Thank you for maintaining one of the best DataViz libraries! 👍

[Lexachoc]

I quickly made a support based on your request.

In below, the legend marker's opacity will not using the opacity value from marker.opacity (defined in data) but from legend.opacity (defined in layout)

layout = {
    legend: {
        opacity: 1
    }
}

but I wonder if we need to be more specific, e.g., put the opacity option inside the marker (or other name)

layout = {
    legend: {
        marker: {
            opacity: 1
        }
    }
}

Or should it not be within layout, but be inside data for each individual trace (But I guess that would be more complex)?

I need more thoughts/advice from more people (especially the Plotly team) so I can further implement it as there are other types of charts that will use the legend. Currently I'm only focusing on scatter plots and bar charts (and histograms).