Legends meta-issue

[mkborregaard]

An overhaul of Plots' legend capabilities would be really useful. Here are some relevant open issues

• contour legend does not scale with clims contour legend does not scale with clims #533
• Legend position with PlotlyJS Legend position with PlotlyJS #574
• shared legend for subplots on some backends shared legend for subplots on some backends #673
• Documentation didn't allow me to figure out how to change the names in legends Documentation didn't allow me to figure out how to change the names in legends #995
• Legend doesn't appear on quiver plot Legend doesn't appear on quiver plot #1589
• aspect_ratio = :equal with legend = false not correct for plotlyjs() aspect_ratio = :equal with legend = false not correct for plotlyjs() #1603
• legendfont does not affect legendtitle legendfont does not affect legendtitle #1856
• markerstrokewidth ignored for legend with PyPlot backend markerstrokewidth ignored for legend with PyPlot backend #2033
• Legend placement with gr appears buggy Legend placement with gr appears buggy #2202
• Horizontal legends Horizontal legends #2206
• legend = :outerright is missing from the documentation legend = :outerright is missing from the documentation #2207
• Legend positioned far from borders overlaping data - GR Legend positioned far from borders overlaping data - GR #2330
• control the size of colorbars? control the size of colorbars? #2345
• Errorbar is missing in the legend Errorbar is missing in the legend #2360
• legend position with outer legends and vertical subplots legend position with outer legends and vertical subplots #2369
• Twinx doesn't combine legends Twinx doesn't combine legends #2417

As well as a desire to share color bars and legends among subplots, allow multiple columns in legends and improvement of the alignment of axes (both with and without link) in layouts with legends.

[isentropic]

#2033 should be fixed

[isentropic]

#1856 closed

[mkborregaard]

Yay @isentropic you're on a roll!

[isentropic]

Perhaps there could be another explicit legend object, that is actually an empty axis with empty plot on it. Similar to what you showed here #673 but it would read as,

plot(
scatter(rand(100,3), legend = false),
scatter(rand(100,3), legend = false),
legend((1:3)),  # actually it is scatter((1:3)', xlim = (4,5), legend = true, framestyle = :none) under the hood
layout = @layout([a b c{0.1w}]))

[isentropic]

That is we could perhaps add a new series type called legend that would actually be an invisible shrunk axis so that all backends can support it. This way it won't feel look as a hack and can be presented in documentation.
legend would be able to have few recipes supporting only shapes and words given to it

[isentropic]

This way we can solve,
#2345
#673
#995
#2369

infixing (inplotting) legend series on top of other axes would allow users to have an explicit control over legends if they wish

[reesepathak]

Just want to emphasize how useful horizontal legends/legends with multiple columns would be.

[isentropic]

Fixed #574