From 813d0bd8c7d4df3b3cba170de54233076b346c1c Mon Sep 17 00:00:00 2001
From: Kara Woo <karawoo@users.noreply.github.com>
Date: Thu, 20 Aug 2020 13:39:25 -0700
Subject: [PATCH] Set file background from plot theme (#4164)

* Add bg argument that defaults to plot.background fill colour

* Add NEWS bullet

* Add test for background color of saved file
---
 DESCRIPTION                  |  3 ++-
 NEWS.md                      |  3 +++
 R/save.r                     |  9 +++++++--
 man/ggsave.Rd                |  4 ++++
 tests/testthat/test-ggsave.R | 14 ++++++++++++++
 5 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/DESCRIPTION b/DESCRIPTION
index 383dd5a511..f07f473b5b 100644
--- a/DESCRIPTION
+++ b/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
diff --git a/NEWS.md b/NEWS.md
index ff33dc03d2..d1dacb18ea 100644
--- a/NEWS.md
+++ b/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()`
diff --git a/R/save.r b/R/save.r
index 51435fbfb6..1bdd11381c 100644
--- a/R/save.r
+++ b/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
diff --git a/man/ggsave.Rd b/man/ggsave.Rd
index 7dfc28f8a0..8d6a6102b4 100644
--- a/man/ggsave.Rd
+++ b/man/ggsave.Rd
@@ -15,6 +15,7 @@ ggsave(
   units = c("in", "cm", "mm"),
   dpi = 300,
   limitsize = TRUE,
+  bg = NULL,
   ...
 )
 }
@@ -43,6 +44,9 @@ If not supplied, uses the size of current graphics device.}
 save images larger than 50x50 inches, to prevent the common error of
 specifying dimensions in pixels.}
 
+\item{bg}{Background colour. If \code{NULL}, uses the \code{plot.background} fill value
+from the plot theme.}
+
 \item{...}{Other arguments passed on to the graphics device function,
 as specified by \code{device}.}
 }
diff --git a/tests/testthat/test-ggsave.R b/tests/testthat/test-ggsave.R
index 03502ca721..4a4fbe0667 100644
--- a/tests/testthat/test-ggsave.R
+++ b/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", {