Boxed geom_text with ggplot2

Question

I am developing a graphic with ggplot2 wherein I need to superimpose text over other graphical elements. Depending on the color of the elements underlying the text, it can b

Answer 1

Update for ggplot2 v0.9

library(ggplot2)
library(proto)

btextGrob <- function (label,x = unit(0.5, "npc"), y = unit(0.5, "npc"), 
    just = "centre", hjust = NULL, vjust = NULL, rot = 0, check.overlap = FALSE, 
    default.units = "npc", name = NULL, gp = gpar(), vp = NULL,  f=1.5) {
    if (!is.unit(x)) 
      x <- unit(x, default.units)
    if (!is.unit(y)) 
      y <- unit(y, default.units)
    grob(label = label, x = x, y = y, just = just, hjust = hjust, 
         vjust = vjust, rot = rot, check.overlap = check.overlap, 
         name = name, gp = gp, vp = vp, cl = "text")
    tg <- textGrob(label = label, x = x, y = y, just = just, hjust = hjust, 
                   vjust = vjust, rot = rot, check.overlap = check.overlap)
    w <- unit(rep(1, length(label)), "strwidth", as.list(label))
    h <- unit(rep(1, length(label)), "strheight", as.list(label))
    rg <- rectGrob(x=x, y=y, width=f*w, height=f*h,
                   gp=gpar(fill="white", alpha=0.3,  col=NA))

    gTree(children=gList(rg, tg), vp=vp, gp=gp, name=name)
  }

GeomText2 <- proto(ggplot2:::GeomText, {
  objname <- "text2"

  draw <- function(., data, scales, coordinates, ..., parse = FALSE, na.rm = FALSE) {
    data <- remove_missing(data, na.rm, 
      c("x", "y", "label"), name = "geom_text2")

    lab <- data$label
    if (parse) {
      lab <- parse(text = lab)
    }

    with(coord_transform(coordinates, data, scales),
      btextGrob(lab, x, y, default.units="native", 
        hjust=hjust, vjust=vjust, rot=angle, 
        gp = gpar(col = alpha(colour, alpha), fontsize = size * .pt,
          fontfamily = family, fontface = fontface, lineheight = lineheight))
    )
  }

})

geom_text2 <- function (mapping = NULL, data = NULL, stat = "identity", position = "identity", 
parse = FALSE,  ...) { 
  GeomText2$new(mapping = mapping, data = data, stat = stat,position = position, 
  parse = parse, ...)
}


qplot(wt, mpg, data = mtcars, label = rownames(mtcars), size = wt) +
   geom_text2(colour = "red")