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

following baptiste v0.9 answer, here's an update with rudimentary control of the box appearance (bgfill, bgalpha, bgcol, expand_w, expand_h):

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, expand_w, expand_h, box_gp = gpar()) {
  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=expand_w*w, height=expand_h*h,
                 gp=box_gp)

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

GeomTextbox <- proto(ggplot2:::GeomText, {
  objname <- "textbox"

  draw <- function(., data, scales, coordinates, ..., parse = FALSE, na.rm = FALSE,
                   expand_w = 1.2, expand_h = 2, bgcol = "grey50", bgfill = "white", bgalpha = 1) {
    data <- remove_missing(data, na.rm, 
                           c("x", "y", "label"), name = "geom_textbox")
    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),
                   box_gp = gpar(fill = bgfill, alpha = bgalpha, col = bgcol),
                   expand_w = expand_w, expand_h = expand_h)
    )
  }

})

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


qplot(wt, mpg, data = mtcars, label = rownames(mtcars), size = wt) +
  theme_bw() +
  geom_textbox()