ggrepel label with transparent background but visible font

Question

Is there somehow a trick to get the font within 'geom_label_repel' alpha=1 but the background maybe alpha=.2?

My problem is, that I have sometimes very dense plots. If I use just text, the text is not readable anymore. If I use label without transparency, the label is perfectly readable but I can not see behind the label. If I choose transparency for the label, then again, the font is no longer readable since it is also transparent and there is not enough contrast against the background.

What I would really love is a white shadow around the font :-)

Here is a minimal example do demonstrate the problem.

library(ggplot2)
library(ggrepel)
library(stringi)

set.seed(1)
df <- data.frame(x=rnorm(10000),
                 y=rnorm(10000),
                 label=NA)
df$label[1:26] <- stringi::stri_rand_strings(26,8)

ggplot(df, aes(x, y)) +
  geom_point(alpha=.3) +
  geom_label_repel(aes(label=label),
                   label.size = NA, 
                   alpha = 0.6, 
                   label.padding=.1, 
                   na.rm=TRUE) +
  theme_bw()

Answer 1

Plot two labels, the second with no fill at all. Set the seed to make sure they perfectly overlap. (Using geom_text_repel doesn't seem to work as the repelling works slightly different.)

ggplot(df, aes(x, y)) +
  geom_point(alpha=.3) +
  geom_label_repel(aes(label=label),
                   label.size = NA, 
                   alpha = 0.6, 
                   label.padding=.1, 
                   na.rm=TRUE,
                   seed = 1234) +
  geom_label_repel(aes(label=label),
                   label.size = NA, 
                   alpha = 1, 
                   label.padding=.1, 
                   na.rm=TRUE,
                   fill = NA,
                   seed = 1234) +
  theme_bw()

Answer 2

ggplot(df, aes(x, y)) +
  geom_point(alpha=.3) +
  geom_label_repel(aes(label=label),
                       label.size = NA,  
                       label.padding=.1, 
                       na.rm=TRUE,
                       fill = alpha(c("white"),0.5))

This worked for me. You can set alpha with a color. Since the fill setting is only the background the text is unaffected. The advantage of this to overlaying the text is you can still use the "repel" to keep text from overlapping and not have to worry about getting two layers lining up properly

Answer 3

Maybe something like the following one:

library(ggplot2)
library(ggrepel)
library(stringi)

set.seed(1)
df <- data.frame(x=rnorm(10000),
                 y=rnorm(10000),
                 label=NA)
df$label[1:26] <- stringi::stri_rand_strings(26,8)

ggplot(df, aes(x, y)) +
    geom_point(alpha=.3) +
    geom_label_repel(aes(label=label),
                     label.size = NA, 
                     alpha = 0.75, 
                     fontface = 'bold', color = 'black',
                     box.padding = 0.80, point.padding = 0.5,
                     na.rm=TRUE) +
    theme_bw()

which gives: