如何使 ragg::agg_png 设备与 ggsave 一起使用？

Question

When I try to use the new-ish ragg::agg_png() device with ggplot2::ggsave() , the image does not appear to save correctly.

Take the following reprex. I make a simple plot and then save it using the agg_png() function directly, and with ggsave() . The image saved with the agg_png() device directly comes out as expected. However, when I use ggsave() , it's almost like the units are being ignored. You can't tell, but there is a tiny image beneath the final code output. In that output, we can see that the image is only 7x7 px, even though inches have been specified by the units. From this blog post , it doesn't seem like anything extra should be required to make ggsave() work beyond setting device = agg_png .

Are there additional parameters I need to specify? Including session info in case there is something system-specific going on.

library(ggplot2)
library(magick)
library(ragg)

p <- ggplot(mtcars, aes(x = mpg, y = disp)) +
  geom_point()

# save plot --------------------------------------------------------------------
agg_png(filename = "agg_png.png", width = 7, height = 7, units = "in",
        res = 320)
print(p)
dev.off()

ggsave("agg_png-ggsave.png", plot = p, device = agg_png, width = 7, height = 7,
       units = "in", dpi = 320)

# look at images ---------------------------------------------------------------
dev <- image_read("agg_png.png")
print(dev)
#> # A tibble: 1 x 7
#>   format width height colorspace matte filesize density
#>   <chr>  <int>  <int> <chr>      <lgl>    <int> <chr>  
#> 1 PNG     2240   2240 sRGB       FALSE    55978 126x126

ggs <- image_read("agg_png-ggsave.png")
print(ggs)
#> # A tibble: 1 x 7
#>   format width height colorspace matte filesize density
#>   <chr>  <int>  <int> <chr>      <lgl>    <int> <chr>  
#> 1 PNG        7      7 sRGB       FALSE      116 28x28

^{Created on 2021-03-01 by the reprex package (v1.0.0)}

Session info

sessioninfo::session_info() #> ─ Session info ─────────────────────────────────────────────────────────────── #> setting value #> version R version 4.0.4 (2021-02-15) #> os macOS Big Sur 10.16 #> system x86_64, darwin17.0 #> ui X11 #> language (EN) #> collate en_US.UTF-8 #> ctype en_US.UTF-8 #> tz America/Chicago #> date 2021-03-01 #> #> ─ Packages ─────────────────────────────────────────────────────────────────── #> package * version date lib source #> assertthat 0.2.1 2019-03-21 [1] CRAN (R 4.0.2) #> backports 1.2.1 2020-12-09 [1] CRAN (R 4.0.2) #> cli 2.3.1 2021-02-23 [1] CRAN (R 4.0.4) #> colorspace 2.0-0 2020-11-11 [1] CRAN (R 4.0.2) #> crayon 1.4.1 2021-02-08 [1] CRAN (R 4.0.2) #> curl 4.3 2019-12-02 [1] CRAN (R 4.0.1) #> DBI 1.1.1 2021-01-15 [1] CRAN (R 4.0.2) #> debugme 1.1.0 2017-10-22 [1] CRAN (R 4.0.2) #> digest 0.6.27 2020-10-24 [1] CRAN (R 4.0.2) #> dplyr 1.0.4 2021-02-02 [1] CRAN (R 4.0.2) #> ellipsis 0.3.1 2020-05-15 [1] CRAN (R 4.0.2) #> evaluate 0.14 2019-05-28 [1] CRAN (R 4.0.1) #> fansi 0.4.2 2021-01-15 [1] CRAN (R 4.0.2) #> farver 2.1.0 2021-02-28 [1] CRAN (R 4.0.4) #> fs 1.5.0 2020-07-31 [1] CRAN (R 4.0.2) #> generics 0.1.0 2020-10-31 [1] CRAN (R 4.0.2) #> ggplot2 * 3.3.3.9000 2021-03-01 [1] Github (tidyverse/ggplot2@dbd7d79) #> glue 1.4.2 2020-08-27 [1] CRAN (R 4.0.2) #> gtable 0.3.0 2019-03-25 [1] CRAN (R 4.0.2) #> highr 0.8 2019-03-20 [1] CRAN (R 4.0.2) #> htmltools 0.5.1.1 2021-01-22 [1] CRAN (R 4.0.2) #> httr 1.4.2 2020-07-20 [1] CRAN (R 4.0.2) #> knitr 1.31.5 2021-02-24 [1] Github (yihui/knitr@ca09938) #> labeling 0.4.2 2020-10-20 [1] CRAN (R 4.0.2) #> lifecycle 1.0.0 2021-02-15 [1] CRAN (R 4.0.2) #> magick * 2.6.0 2021-01-13 [1] CRAN (R 4.0.2) #> magrittr 2.0.1 2020-11-17 [1] CRAN (R 4.0.2) #> mime 0.10 2021-02-13 [1] CRAN (R 4.0.2) #> munsell 0.5.0 2018-06-12 [1] CRAN (R 4.0.2) #> pillar 1.5.0 2021-02-22 [1] CRAN (R 4.0.4) #> pkgconfig 2.0.3 2019-09-22 [1] CRAN (R 4.0.2) #> png 0.1-7 2013-12-03 [1] CRAN (R 4.0.2) #> purrr 0.3.4 2020-04-17 [1] CRAN (R 4.0.2) #> R6 2.5.0 2020-10-28 [1] CRAN (R 4.0.2) #> ragg * 1.1.0.9000 2021-03-01 [1] Github (r-lib/ragg@05bd5a7) #> Rcpp 1.0.6 2021-01-15 [1] CRAN (R 4.0.2) #> reprex 1.0.0 2021-01-27 [1] CRAN (R 4.0.2) #> rlang 0.4.10 2020-12-30 [1] CRAN (R 4.0.2) #> rmarkdown 2.7.2 2021-03-01 [1] Github (rstudio/rmarkdown@c0b8584) #> rstudioapi 0.13 2020-11-12 [1] CRAN (R 4.0.2) #> scales 1.1.1 2020-05-11 [1] CRAN (R 4.0.2) #> sessioninfo 1.1.1 2018-11-05 [1] CRAN (R 4.0.2) #> stringi 1.5.3 2020-09-09 [1] CRAN (R 4.0.2) #> stringr 1.4.0 2019-02-10 [1] CRAN (R 4.0.2) #> styler 1.3.2 2020-02-23 [1] CRAN (R 4.0.2) #> systemfonts 1.0.1 2021-02-09 [1] CRAN (R 4.0.2) #> textshaping 0.3.1 2021-02-22 [1] CRAN (R 4.0.4) #> tibble 3.1.0 2021-02-25 [1] CRAN (R 4.0.2) #> tidyselect 1.1.0 2020-05-11 [1] CRAN (R 4.0.2) #> utf8 1.1.4 2018-05-24 [1] CRAN (R 4.0.2) #> vctrs 0.3.6 2020-12-17 [1] CRAN (R 4.0.2) #> withr 2.4.1 2021-01-26 [1] CRAN (R 4.0.2) #> xfun 0.21 2021-02-10 [1] CRAN (R 4.0.2) #> xml2 1.3.2 2020-04-23 [1] CRAN (R 4.0.2) #> yaml 2.2.1 2020-02-01 [1] CRAN (R 4.0.2) #> #> [1] /Library/Frameworks/R.framework/Versions/4.0/Resources/library

Answer 1

Default units for ragg device is in px . Change it to inches and try this

p <- ggplot(mtcars, aes(x = mpg, y = disp)) +
  geom_point()

png <- function(...) ragg::agg_png(..., res = 300, units = "in")
ggsave("agg_png-ggsave.png", plot = p, device = png, width = 3, height = 3, units = "in",
       dpi = 100) # units = "in"

ggs <- image_read("agg_png-ggsave.png")
print(ggs)

Actually, you can just try this

ggsave("agg_png-ggsave.png", p, device = ragg::agg_png, res = 300,  units = "in") 
ggs <- image_read("agg_png-ggsave.png")
print(ggs)