Configurable width of the symbol area of legends

[s417-lama]

Problem

It was hard to distinguish different line types (dash or dashdot) in legends because the width of legend items were small.

Scatter plot of dash and dashdot lines:

What I did

I added legend.itemwidth option to configure the width of legend items.

By setting legend.itemwidth = 60:

The option name itemwidth might be controversial; for example, in matplotlib, the corresponding option name is handlelength.

[archmoj]

Thanks for the PR. Looking good to me at first glance.
In respect to adding this new attribute to the API, let me request a review from @nicolaskruchten and @alexcjohnson.

[archmoj]

@s417-lama we are planning next plotly.js minor (possibly next week) to include new features like this one.
Do you have time to address the remaining comments, so that we could include this feature?

[s417-lama]

@archmoj Thank you for reviewing. That sounds nice!
I addressed all of the above comments in 1977f12.

[archmoj]

@archmoj Thank you for reviewing. That sounds nice!
I addressed all of the above comments in 1977f12.

@s417-lama
Thanks for the quick improvement.
Nicely done!
💃

[karolpiczak]

@archmoj

Is there some architectural reason why itemwidth must be at least 30? In some of the plots I would like to have shorter handles, I don't see an easy way to override this without manually creating a legend using manual annotations.

[bklingen]

@archmoj

Following up on this, why is itemwidth restricted to be at least 30. I would love to create legends using e.g., itemwidth: 20 in layout.legend.