Can we add shadows to (dashed) lines in R (ggplot2

Question

I was asked to add shadows to a dashed-line in R. It would be similar to this image I found on-line, except it is for non-solid lines:

I did not find any specific control/package for this purpose. If it was a solid line that I needed a shadow for, I would have simulated the shadow using another line with different opacity and thickness. But it seems for the non-solid lines (dashed, dotted, etc) this workaround won't work, since their gaps won't match as you change the thickness.

Any ideas?

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Image is copied from here only for the sake of clarity.

Answer 1

You can only tweak this like

df <- data.frame(x = 1:20, y = cumsum(rnorm(20)))
ggplot(df, aes(x = x, y = y)) +
  geom_line(aes(x = x+0.15, y = y-0.15), alpha = 0.2, lwd = 1.2, linetype = 2) +
  geom_point(aes(x = x+0.15, y = y-0.15), alpha = 0.1, size = 2.5) +
  geom_line(lwd = 1, linetype = 2) + 
  geom_point(size = 2.5) +
  theme_bw()