directlabels - utility.function - Positioning Method - bumpup

Sequentially bump labels up, starting from the bottom, if they collide with the label underneath.

bumpup <- function(d,...){
  d <- calc.boxes(d)[order(d$y),]
  "%between%" <- function(v,lims)lims[1]<v&v<lims[2]
  obox <- function(x,y){
    tocheck <- with(x,c(left,(right-left)/2+left,right))
    tocheck %between% with(y,c(left,right))
  }
  for(i in 2:nrow(d)){
    dif <- d$bottom[i]-d$top[i-1]
    ## here we are trying to test if box i can possibly collide with
    ## the box below it! Originally we checked if the bottom points of
    ## this box fall in the box below it, but this causes problems
    ## since we are reassigning box positions. If all boxes start at
    ## the same place, 2 will get moved up, 3 will not since its
    ## bottom points are no longer inside box 2. Solution: Look at box
    ## left and right limits and see if they collide!

    ## GOTCHA: If all the boxes are exactly the same size, on top of
    ## each other, then if we only examine left and right points of
    ## each box, none of the boxes will be detected as
    ## overlapping. One way to fix this is change > to >= in %between%
    ## but this is a bad idea since you can have boxes right next to
    ## each other that we don't want to move, that would be detected
    ## as overlapping. Solution: use the midpoint of the box as well!
    overlap <- c(obox(d[i,],d[i-1,]),obox(d[i-1,],d[i,]))
    if(dif<0&&any(overlap)){
      d$bottom[i] <- d$bottom[i]-dif
      d$top[i] <- d$top[i]-dif
      d$y[i] <- d$y[i]-dif
    }
  }
  d
}