Options of a binned scale’s legend — ggplot2’s guide_bins() (#409):
keys stacked edge to edge, labelled at the bin boundaries along a small
axis. Apply with GGPlot::guide_bins.
Options of a continuous colour / fill legend — ggplot2’s
guide_colourbar(), or guide_coloursteps() when steps is set
(#409). Apply with GGPlot::guide_colourbar.
A legend entry drawn by your own code — ggplot2’s guide_custom(grob, width, height, title) (#409): a width × height px box in the legend
stack (under title, if any), handed to draw to paint with the usual
DrawBackend calls. Add with
GGPlot::guide_custom.
Fixed values a legend’s keys are drawn with, whatever the data maps
(ggplot2’s override.aes, #409) — e.g. opaque, larger keys for a
scatter plot drawn with small, translucent points. None keeps the key’s
own value.