ggoutlines

The ggoutlines package extends the popular ggplot2 plotting package by providing popular geometry layers and theme elements that can be outlined.

Installation

You can install the development version of ggoutlines from GitHub with:

# install.packages("devtools")
devtools::install_github("teunbrand/ggoutlines")

Warning {ggoutlines} has adopted the ‘linewidth’ aesthetic in the development version of the {ggplot2} package. It is not compatible with earlier versions of {ggplot2}.

Example

The idea here is that there are variants of classic ggplot2 functions that draw the same thing, but with outlines. Below is a simple example of a lineplot, where the lines have white outlines.

library(ggoutlines)
#> Loading required package: ggplot2

ggplot(economics_long, aes(date, value01, colour = variable)) +
  geom_path_outline(
    stroke_colour = "white",
    stroke_linewidth = 2
  )

Some extra attention is paid to the transparency settings, ensuring that everything works ‘as expected’ with semi-transparent colours.

df <- data.frame(
  x = c(0.33, 0.66),
  y = c(0.66, 0.33),
  lab = c("Hello there,", "README reader")
)

ggplot(df, aes(x, y, label = lab, colour = lab)) +
  geom_text_outline(
    stroke_colour = "black",
    stroke_linewidth = 3, alpha = 0.3,
    size = 20, hjust = c(0, 1),
    show.legend = FALSE
  ) +
  ylim(c(-1, 2))

Most geoms have to option to either turn of or turn on grouped outlines. Turning it off gives the layer as a whole an outline, whereas turning it on will give groups outlines.

p <- ggplot(mpg, aes(displ, fill = factor(cyl)))

p + geom_histogram_outline(by_group = TRUE, bins = 20) +
  labs(title = "by_group = TRUE")
p + geom_histogram_outline(by_group = FALSE, bins = 20) +
  labs(title = "by_group = FALSE")

Aside from providing geom layers, you can also use outlined theme elements.

ggplot(mpg, aes(displ, hwy, colour = factor(cyl))) +
  geom_point_outline(alpha = 0.3) +
  labs(title = "Engine displacement versus highway miles") +
  theme(
    plot.title        = element_text_outline(colour = "white"),
    legend.background = element_rect_outline(colour = "white", fill = NA),
    panel.grid.major  = element_line_outline(
      stroke_colour = "white", colour = "grey92"
    )
  )

Limitations

At the moment of writing, not many graphics devices in R support the use of the recent additions in the {grid} package (> R4.2.0). Since {ggoutlines} relies on this functionality, it is recommended to use the ‘cairo-png’ device for raster output.

Here is a list of missing functionality:

• The linetype for lines is not properly implemented for the outlines.

Related packages

Some packages that implement similar functionality as {ggoutlines} are shadowtext, ggtrace and ggborderline.