[FR] Support shadowtext / text background

[albert-ying]

There are currently multiple implementations for the geom_text with border. For example, shadowtext. ggrepel also take a bg.color argument that can produce a similar effect.

https://guangchuangyu.github.io/2017/11/shadow-text-effect-in-grid-and-ggplot2-graphics/
https://stackoverflow.com/questions/56798482/how-to-combine-repelling-labels-and-shadow-or-halo-text-in-ggplot2

This could be helpful for geomtextpath, especially when gap = FALSE, or when plot with other geom layers.

Also could help my previous problem #55 , to better separate the text and line when vjust is not working.

Thank you so much!

[teunbrand]

I like the idea, but I don't think it makes sense for us to implement as {ggfx} can do this (and more) without us having to lift a finger.

library(ggfx)
#> Warning: package 'ggfx' was built under R version 4.1.1
library(geomtextpath)
#> Loading required package: ggplot2

t <- seq(5, -1, length.out = 1000) * pi

spiral <- data.frame(x    = sin(t) * 1:1000, 
                     y    = cos(t) * 1:1000,
                     text = paste("Like a circle in a spiral,",
                                  "like a wheel within a wheel,",
                                  "never ending or beginning,",
                                  "on an ever spinning reel")
)

ggplot(spiral, aes(x, y, label = text)) +
  with_outer_glow(
    geom_textpath(size = 7, vjust = 2, text_only = TRUE, colour = "white"),
    sigma = 0, expand = 2
  ) +
  coord_equal(xlim = c(-1500, 1500), ylim = c(-1500, 1500))

^{Created on 2022-01-15 by the reprex package (v2.0.1)}

[teunbrand]

A small note: once R4.2.0 comes out, it might make sense to do outlined text as it becomes part of the grid package. See https://www.stat.auckland.ac.nz/~paul/Reports/GraphicsEngine/paths/paths.html, 2nd paragraph, 4th example

[albert-ying]

Wow thank you so much! I didn't know that the ggfx can work here.