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Interactive point labels with gridSVG and ggplot2 v.0.9.0

I'd like to label points in a ggplot interactively, so that mousing over a point shows a label.

I'm trying to adapt the answer given in this question so that it works in the latest version of ggplot2. Influenced by comments on the ggplot google group, here, I used the latest version of geom-point-.r as a template, adding a "label" field to the gp argument in various places. Then I copied the remaining code from kohske's answer. But it doesn't work -- there aren't any labels in the resulting svg, and I can't figure out why.

I did notice that everything in point_grobs_labels is null, and when I look at grid.get(point_grob_names[1])$gp, there is no label field...

library(ggplot2)
library(gridSVG)
library(proto)
library(rjson)
 
geom_point2 <- function (mapping = NULL, data = NULL, stat = "identity", 
                         position = "identity",
                         na.rm = FALSE, ...) {
  ggplot2:::GeomPoint$new(mapping = mapping, data = data, stat = stat, 
                          position = position, 
                          na.rm = na.rm, ...)
}
 
GeomPoint2 <- proto(ggplot2:::Geom, {
  objname <- "point"
 
  draw_groups <- function(., ...) .$draw(...)
  draw <- function(., data, scales, coordinates, na.rm = FALSE, ...) {    
    data <- remove_missing(data, na.rm, 
                           c("x", "y", "size", "shape"), name = "geom_point")
    if (empty(data)) return(zeroGrob())
 
    with(coord_transform(coordinates, data, scales), 
         ggname(.$my_name(), pointsGrob(x, y, size=unit(size, "mm"), pch=shape, 
                                        gp=gpar(
                                          col=alpha(colour, alpha),
                                          fill = alpha(fill, alpha),  
                                          label = label, 
                                          fontsize = size * .pt)))
    )
  }
 
  draw_legend <- function(., data, ...) {
    data <- aesdefaults(data, .$default_aes(), list(...))
 
    with(data,
         pointsGrob(0.5, 0.5, size=unit(size, "mm"), pch=shape, 
                    gp=gpar(
                      col = alpha(colour, alpha), 
                      fill = alpha(fill, alpha), 
                      label = label,
                      fontsize = size * .pt)
         )
    )
  }
 
  default_stat <- function(.) StatIdentity
  required_aes <- c("x", "y")
  default_aes <- function(.) aes(shape=16, colour="black", size=2, 
                                 fill = NA, alpha = NA, label = NA)
 
})
 
p <- ggplot(mtcars, aes(mpg, wt, label = rownames(mtcars))) + geom_point2() + facet_wrap(~ gear)
print(p)
 
grob_names <- grid.ls(print = FALSE)$name
point_grob_names <- sort(grob_names[grepl("point", grob_names)])
point_grobs_labels <- lapply(point_grob_names, function(x) grid.get(x)$gp$label)  
 
jlabel <- toJSON(point_grobs_labels)
 
grid.text("value", 0.05, 0.05, just = c(0, 0), name = "text_place", gp = gpar(col = "red"))
 
script <- '
var txt = null;
function f() {
var id = this.id.match(/geom_point2.([0-9]+)\\.points.*\\.([0-9]+)$/);
txt.textContent = label[id[1]-1][id[2]-1];
}
 
window.addEventListener("load",function(){
var es = document.getElementsByTagName("circle");
for (i=0; i<es.length; ++i) es[i].addEventListener("mouseover", f, false);
 
txt = (document.getElementById("text_place").getElementsByTagName("tspan"))[0];
 
},false);
'
 
grid.script(script = script)
grid.script(script = paste("var label = ", jlabel))
 
gridToSVG()