geom_stext.r

library(ggplot2)
library(scales)
library(dplyr)

# http://www.stuff.co.nz/national/86458731/Cheviot-earthquake-Tracing-the-source-of-the-7-5-magnitude-quake-and-its-aftermath?utm_source=dlvr.it&utm_medium=twitter

eqs <- data.frame(
  energy = c(48.99, 13.34, 2.67, 6.25, 4.93, 2.71, 4.73, 16.38),
  period = c("Nov 14 2016", "Earlier 2016", paste("All", 2015:2010)),
  stringsAsFactors = FALSE)

eqs <- eqs %>%
  mutate(period = factor(period, levels = period)) %>%
  arrange(desc(period)) %>%
  mutate(cumenergy = cumsum(energy),
         centres = cumenergy - energy / 2)


leg <- guide_legend(reverse = TRUE)


library(grid)
stextGrob <- function (label, x = unit(0.5, "npc"), y = unit(0.5, "npc"), r=0.03, colour="black",
                       just = "centre", hjust = NULL, vjust = NULL, rot = 0, check.overlap = FALSE, 
                       default.units = "npc", name = NULL, gp = gpar(), vp = NULL){
  
  let <- textGrob("a", gp=gp, vp=vp)
  wlet <- grobWidth(let)
  hlet <- grobHeight(let)
  
  tg <- textGrob(label=label, x=x, y=y, gp=gpar(col=colour),
                 just = just, hjust = hjust, vjust = vjust, rot = rot,
                 check.overlap = check.overlap, 
                 default.units = default.units)
  
  tgl <- c(lapply(seq(0, 2*pi, length=36), function(theta){
    
    textGrob(label=label,x=unit(x, "native")+cos(theta)*r*wlet,
             y=unit(y, "native")+sin(theta)*r*hlet, gp=gpar(col="white"),
             just = just, hjust = hjust, vjust = vjust, rot = rot,
             check.overlap = check.overlap, 
             default.units = default.units)
    
  }), list(tg))
  
  
  g <- gTree(children=do.call(gList, tgl), vp=vp, name=name, gp=gp)
  
}

grid.stext <- function(...){
  g <- stextGrob(...)
  grid.draw(g)
  invisible(g)
}



GeomStext <- ggproto("GeomStext", Geom,
                    required_aes = c("x", "y", "label"),
                    default_aes = aes(size = 5),
                    
                    draw_key = function (data, params, size) 
                    {
                      stextGrob(label=data$label,  data$x, data$y, size=data$size, colour=data$colour)
                    },
                    
                    draw_group = function(data, panel_scales, coord) {
                      coords <- coord$transform(data, panel_scales)     
                      stextGrob(label=coords$label,  coords$x, coords$y, colour=coords$colour)
                    }
)

geom_stext <- function(mapping = NULL, data = NULL, stat = "identity",
                      position = "identity", na.rm = FALSE, show.legend = NA, 
                      inherit.aes = TRUE, ...) {
  layer(
    geom = GeomStext, mapping = mapping,  data = data, stat = stat, 
    position = position, show.legend = show.legend, inherit.aes = inherit.aes,
    params = list(na.rm = na.rm, ...)
  )
}


ggplot(eqs, aes(x = 1, weight = energy, fill = period)) +
  geom_bar(width = 1, colour = "grey50") +
  geom_stext(x = 1.3, aes(y = centres, colour=period, label = paste0(energy, "%"))) +
  coord_polar(theta = "y") +
  scale_fill_brewer(palette = "Oranges", direction = -1, guide = leg) +
  scale_color_brewer(palette = "Blues", direction = 1, guide = leg)    +
  theme_minimal(base_family = "Arial") +
  theme(axis.ticks = element_blank(),
        axis.text = element_blank(),
        axis.title = element_blank(),
        plot.caption = element_text(hjust = 0.5)) +
  labs(fill = "", colour = "", 
       caption = "Source: http://www.stuff.co.nz/national/86458731/\nCheviot-earthquake-Tracing-the-source-of-the-7-5-magnitude-quake-and-its-aftermath\nSupplied by John Holdaway") +
  ggtitle("Half the earthquake energy released since 2010 came in a single day",
          subtitle = "Energy released in all New Zealand earthquakes, 2010-2016")