Margin tweaks for legends

[hadley]

Currently you can only control the overall margin of the legend, but ideally you'd be able to control each of t/r/b/l separately. Then the defaults need to be adjusted so that you can easily align a legend to either the top-right or the bottom-left of the plotting area.

[thomasp85]

My suggestion would be to go with the CSS approach and let users specify either one, two, or four values. Then we could have a valid.margin() function that automatically expands the unit vector.

Don't know the preferred approach to adapting the defaults to the user-set justification?

[thomasp85]

This approach to margins should of course be applied to all margin specifications. That is, panel.margin, plot.margin, and the margin argument in element_text() should be changed as well.

Come to think of it - panel.margin should really be called panel.spacing - the same holds for legend.margin

I'll hold off on anything before you comment on these thoughts...

[thomasp85]

Actually the margin function would just need a little tweaking to support the functionality in element_text - And it could then be applied for the other margins as well

Someting like:

margin <- function(t = 0, r = t, b = t, l = r, unit = "pt") {
  structure(unit(c(t, r, b, l), unit), class = c("margin", "unit"))
}

should do it...

[hadley]

Right — the way to do this is to implement more margin() helpers. I think changing how margin() works is not great at this point (I did deliberately choose the current behaviour of defaulting to 0), but we could certainly add another function.

I agree that panel.margin and legend.margin would be better off as panel.spacing and legend.spacing, but I think changing them now would be a lot of work. I think we should just adjust the docs to clarify that these are internal margins only.

[hadley]

1. Existing behaviour of legend.margin needs to become like panel.margin and only control the spacing between multiple legends
2. That makes legend.margin and panel.margin somewhat confusing because they really should be legend.spacing and panel.spacing. We could leave as is and make clear in documentation, or change names with code in theme() to work with either old or new specification.
3. We'll also need a new legend.box.margin that controls the margin between the legend box and the panel.
4. We could consider adding legend.box.background but that would require an additional margin theme setting so you could independently control the margin inside and outside the box.

[assaron]

Hi,

Is it possible to keep panel.margin option too, but with throwing a deprecation warning? I have the package in Bioconductor that uses this option and I can't put dependence on the >=2.2.0 ggplot verision, as it's not yet realeased, and can't just ignore this, as it will break my package soon.

[thomasp85]

This is how it works currently - It will throw a warning and reassign the value to panel.spacing