This function does it's best attempt to take whatever you provide it and turn it into a gtable. It is primarily meant to convert ggplot plots into gtables, but it will also take any grid object (grob), a recorded R base plot, or a function that generates an R base plot.
plot_to_gtable(plot)The plot or other graphics object to convert into a gtable. Here, plot can be an
object of the following classes: ggplot, recordedplot,
grob, or gtable. Alternatively, plot can be
a function creating a plot when called (see examples for plot_grid()).