Plotting with grobs using {gggrid}

library(grid)
library(gggrid)
#> Loading required package: ggplot2
library(svgparser)

Use grobs as points in {ggplot} using {gggrid}

I highly recommend reading Paul Murrel’s Report on {gggrid} and other techniques for getting grobs into ggplots.

Other approaches are discussed (e.g. using {egg}) but here I’ll demonstrate using gggrid.

# remotes::install_github('https://github.com/pmur002/gggrid')
library(grid)
library(gggrid)
library(svgparser)


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Loat SVG as a grob
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
rlogo_url <- 'https://www.r-project.org/logo/Rlogo.svg'
g <- svgparser::read_svg(rlogo_url)
g$vp <- grid::viewport(x = 0.8, y = 0.8, width = unit(4, 'cm'), height = unit(4, 'cm'))


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Define a callfback function to use within each panel.
# See 
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
func <- function(data, coords) {
  
  position_grob <- function(row) {
    gnew <- g
    gnew$vp$x      <- unit(row[['x']], 'npc')
    gnew$vp$y      <- unit(row[['y']], 'npc')
    gnew$vp$width  <- unit(row[['size']]/4, 'cm')
    gnew$vp$height <- unit(row[['size']]/4, 'cm')
    gnew$name <- strftime(Sys.time(), "%H%M%OS6") # Enforce unique name per grob. 
    gnew
  }
  
  grobs <- lapply(seq(nrow(coords)), function(idx) {position_grob(coords[idx, ])})
  do.call(grid::grobTree, grobs)
}


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Plot wih a `gggrid::grid_panel()`
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ggplot(mtcars, aes(mpg, wt, size = cyl)) + 
  grid_panel(func) + 
  theme_bw() +
  labs(title = "{svgparser} + {gggrid}: Custom ggplot points with SVG")