Set file background from plot theme

DESCRIPTION

@@ -63,7 +63,8 @@ Suggests:
     sf (>= 0.7-3),
     svglite (>= 1.2.0.9001),
     testthat (>= 2.1.0),
-    vdiffr (>= 0.3.0)
+    vdiffr (>= 0.3.0),
+    xml2
 Enhances: sp
 License: GPL-2 | file LICENSE
 URL: http://ggplot2.tidyverse.org, https://github.com/tidyverse/ggplot2

NEWS.md

@@ -1,5 +1,8 @@
 # ggplot2 (development version)
 
+* `ggsave()` now sets the default background to match the fill value of the
+  `plot.background` theme element (@karawoo, #4057)
+
 * Extended `stat_ecdf()` to calculate the cdf from either x or y instead from y only (@jgjl, #4005).
 
 * Fixed a bug in `labeller()` so that `.default` is passed to `as_labeller()`

R/save.r

@@ -38,6 +38,8 @@
 #' @param limitsize When `TRUE` (the default), `ggsave()` will not
 #'   save images larger than 50x50 inches, to prevent the common error of
 #'   specifying dimensions in pixels.
+#' @param bg Background colour. If `NULL`, uses the `plot.background` fill value
+#'   from the plot theme.
 #' @param ... Other arguments passed on to the graphics device function,
 #'   as specified by `device`.
 #' @export
@@ -74,7 +76,7 @@
 ggsave <- function(filename, plot = last_plot(),
                    device = NULL, path = NULL, scale = 1,
                    width = NA, height = NA, units = c("in", "cm", "mm"),
-                   dpi = 300, limitsize = TRUE, ...) {
+                   dpi = 300, limitsize = TRUE, bg = NULL, ...) {
 
   dpi <- parse_dpi(dpi)
   dev <- plot_dev(device, filename, dpi = dpi)
@@ -84,8 +86,11 @@ ggsave <- function(filename, plot = last_plot(),
   if (!is.null(path)) {
     filename <- file.path(path, filename)
   }
+  if (is_null(bg)) {
+    bg <- calc_element("plot.background", plot_theme(plot))$fill
+  }
   old_dev <- grDevices::dev.cur()
-  dev(filename = filename, width = dim[1], height = dim[2], ...)
+  dev(filename = filename, width = dim[1], height = dim[2], bg = bg, ...)
   on.exit(utils::capture.output({
     grDevices::dev.off()
     if (old_dev > 1) grDevices::dev.set(old_dev) # restore old device unless null device

tests/testthat/test-ggsave.R

@@ -28,6 +28,20 @@ test_that("ggsave restores previous graphics device", {
   expect_identical(old_dev, dev.cur())
 })
 
+test_that("ggsave uses theme background as image background", {
+  path <- tempfile()
+  on.exit(unlink(path))
+  p <- ggplot(mtcars, aes(disp, mpg)) +
+    geom_point() +
+    coord_fixed() +
+    theme(plot.background = element_rect(fill = "#00CCCC"))
+  ggsave(path, p, device = "svg", width = 5, height = 5)
+  img <- xml2::read_xml(path)
+  # Find background rect in svg
+  bg <- as.character(xml2::xml_find_first(img, xpath = "d1:rect/@style"))
+  expect_true(grepl("fill: #00CCCC", bg))
+})
+
 # plot_dim ---------------------------------------------------------------
 
 test_that("guesses and informs if dim not specified", {