directlabels - utility.function - Positioning Method - polygon.method

Make a Positioning Method that places non-overlapping speech polygons at the first or last points.

polygon.method <- function(method, space, data.col, na.col){
  list(method, "calc.boxes",
       function(d,...){
         for(xy in c("x", "y")){
           d[[sprintf("%s.%s", data.col, xy)]] <- d[[xy]]
           d[[sprintf("%s.%s", na.col, xy)]] <- NA
         }
         d$x <- d$x + space
         d
       },
       "reduce.cex.lr",
       dl.trans(h=h*1.5),
       "calc.borders",
       qp.labels("y","bottom","top", make.tiebreaker("x","y"), ylimits),
       "calc.borders", draw.polygons)
}