R plots: Is there a way to draw a border, shadow or buffer around text labels?

Question

I want to plot a label over a line in a monochrome graphic. So I need small white border on each letter of the label.

The border or background of rectangle of the text label is not useful because it hides a lot of the plotted data.

Is there a way to put a border, shadow or buffer around text labels in R plots?

shadowtext <- function(x, y=NULL, labels, col='white', bg='black',
                   theta= seq(pi/4, 2*pi, length.out=8), r=0.1, ... ) {

  xy <- xy.coords(x,y)
  xo <- r*strwidth('x')
  yo <- r*strheight('x')

  for (i in theta) {
    text( xy$x + cos(i)*xo, xy$y + sin(i)*yo, labels, col=bg, ... )
  }
  text(xy$x, xy$y, labels, col=col, ... )
}

pdf(file="test.pdf", width=2, height=2); par(mar=c(0,0,0,0)+.1)
  plot(c(0,1), c(0,1), type="l", lwd=20, axes=FALSE, xlab="", ylab="")
  text(1/6, 1/6, "Test 1")
  text(2/6, 2/6, "Test 2", col="white")
  shadowtext(3/6, 3/6, "Test 3")
  shadowtext(4/6, 4/6, "Test 4", col="black", bg="white")
  shadowtext(5/6, 5/6, "Test 5", col="black", bg="white", theta = seq(pi/4, 2*pi, length.out=24))
dev.off()

The code above use the solution from koekenbakker. This is fine for PNG graphic, but I need a different approach for high resolution PDF.

Answer 1

You can try this 'shadowtext' function that draws a halo or border around the text by printing it several times with a slight offset in a different colour. All credits to Greg Snow here.

shadowtext <- function(x, y=NULL, labels, col='white', bg='black', 
                       theta= seq(0, 2*pi, length.out=50), r=0.1, ... ) {

    xy <- xy.coords(x,y)
    xo <- r*strwidth('A')
    yo <- r*strheight('A')

    # draw background text with small shift in x and y in background colour
    for (i in theta) {
        text( xy$x + cos(i)*xo, xy$y + sin(i)*yo, labels, col=bg, ... )
    }
    # draw actual text in exact xy position in foreground colour
    text(xy$x, xy$y, labels, col=col, ... )
}

# And here is an example of use:
# pdf(file="test2.pdf", width=2, height=2); par(mar=c(0,0,0,0)+.1)
plot(c(0,1), c(0,1), type="n", lwd=20, axes=FALSE, xlab="", ylab="")

rect(xleft = 0.5, xright = 1, ybottom = 0, ytop = 1, col=1)
text(1/6, 1/6, "Test 1")
shadowtext(2/6, 2/6, "Test 2", col='red', bg="blue")
shadowtext(3/6, 3/6, "Test 3", cex=2)

# `r` controls the width of the border
shadowtext(5/6, 5/6, "Test 4", col="black", bg="white", cex=4, r=0.2)
# dev.off()

Answer 2

I needed to do this for a map in R and ended up using the "raster" package to draw halos around text labels.

http://rpackages.ianhowson.com/cran/raster/man/text.html

For example,

library(raster)

text(Points, labels = Points$Labels, halo = TRUE, hw = 0.08, hc = "white", cex = 0.8)
# hw = halo width
# hc = halo color

Answer 3

The shadowtext package can be used to draw outline or shadow around text for ggplot2 plots.

library(ggplot2)
library(shadowtext)

jet.colors <- colorRampPalette(c("#00007F", "blue", "#007FFF", "cyan", "#7FFF7F", 
                                 "yellow", "#FF7F00", "red", "#7F0000"))

### Note: jet (rainbow) is not color-blind friendly, not perceptually uniform, and can be misleading 
# so please don't use it for your plots
# https://blogs.egu.eu/divisions/gd/2017/08/23/the-rainbow-colour-map/
# https://www.nature.com/articles/519291d
# Choose viridis instead https://cran.r-project.org/web/packages/viridis/vignettes/intro-to-viridis.html
# I only use jet here for the demonstration of the `shadowtext` package.

ggplot(faithfuld, aes(waiting, eruptions)) +
  geom_raster(aes(fill = density)) +
  scale_fill_gradientn(colors = jet.colors(7)) +
  geom_shadowtext(aes(x = 75, y = 4.5),
    label = "White text with black outline\nwill be visible on any background",
    check_overlap = TRUE,
    size = 8) +
  theme_minimal()

^{Created on 2018-10-14 by the reprex package (v0.2.1.9000)}

Answer 4

I wrote a similar function for text fields, which also works on logarithmic scales.

install.packages("berryFunctions")
library("berryFunctions")
?textField

This may be considered nicer for vector graphics. Here are some examples:

PS: If you want to contribute: https://github.com/brry/berryFunctions