We needed a customized version of ggplot2's print.ggplot2
,
because we need to build plots from the intermediate results of
ggplot_build
rather than from a gg
object.
plot_ggplot_build(b, newpage = is.null(vp), vp = NULL)
A list resulting from ggplot_build
draw new (empty) page first?
viewport to draw plot in