Device Size for coord_fixed Ggplot

coord-fixed_dims.R

# Compute Device Size To Fully Fill With Plot
#
# This is not tested extensively and I know very little about messing with
# grid.
#
# GPL-2
#
# @param gtable e.g. as produced by `ggplotGrob(ggplot() ...)`
# @param din device dimension in inches, ideally use defaults to avoid
#   calculation issues with npc units.
# @return numeric(2) containing width and height of device that would be fully
#  occupied by provided gtable when rendered.

gtable_dim <- function(gtable, din=par()[['din']]) {
  gw <- gtable::gtable_width(gtable)
  gh <- gtable::gtable_height(gtable)
  wunits <- attr(gw$arg1, 'unit')
  wknown <- Reduce('+', grid::convertX(gw$arg1[wunits != 'null'], 'inches'))
  wnull <- Reduce('+', gw$arg1[wunits == 'null'])

  hunits <- attr(gh$arg1, 'unit')
  hknown <- Reduce('+', grid::convertX(gh$arg1[hunits != 'null'], 'inches'))
  hnull <- Reduce('+', gh$arg1[hunits == 'null'])

  null.size <- min(c((din[1] - wknown) / wnull, (din[2] - hknown) / hnull))
  c(wknown + null.size * wnull, hknown + null.size * hnull)
}
# Usage example

set.seed(1221)
dev.new(width=5, height=5)
dat <- data.frame(x=rnorm(100), y=rnorm(100), type=rep(1:2, each=50))
p <- ggplot(dat) + geom_point(aes(x, y)) +
  facet_wrap(~type) + coord_fixed() +
  theme(plot.background = element_rect(fill='red'))
print(p, new.page=FALSE)
dim <- gtable_dim(ggplotGrob(p))
dev.new(width=dim[1], height=dim[2])
p