Hack to offset tip labels in plotted fan tree

Yesterday I received the following inquiry about phytools:

“I am using your package to create stochastic character maps in R and I have not had any luck offsetting the species names when creating my fan trees. Do you have any suggestions about how this can be fixed, it would be greatly appreciated.”

In fact, label offset is not an option in plot.simmap(...,type="fan"); however the following is a fairly elegant hack I thought of this morning:

library(phytools)
library(geiger)
data(anoletree) ## our tree that we will use for this example
anoletree

## 
## Phylogenetic tree with 82 tips and 81 internal nodes.
## 
## Tip labels:
##  Anolis_ahli, Anolis_allogus, Anolis_rubribarbus, Anolis_imias, Anolis_sagrei, Anolis_bremeri, ...
## 
## The tree includes a mapped, 6-state discrete character with states:
##  CG, GB, TC, TG, Tr, Tw
## 
## Rooted; includes branch lengths.

## first plot the tree with transparent color:
h<-max(nodeHeights(anoletree))
offset.factor<-1.05 ## increase this for greater offset
plotTree(rescale(anoletree,model="depth",depth=offset.factor*h),
    color="transparent",ftype="i",type="fan",fsize=0.7,lwd=3)
par(fg="transparent")
obj<-get("last_plot.phylo",envir=.PlotPhyloEnv)
plot(anoletree,type="fan",fsize=0.7,ftype="i",add=TRUE,
    xlim=obj$x.lim,ylim=obj$y.lim,lwd=3)

## no colors provided. using the following legend:
##        CG        GB        TC        TG        Tr        Tw 
##   "black"     "red"  "green3"    "blue"    "cyan" "magenta"

par(fg="black")
## add a legend
states<-sort(unique(getStates(anoletree,"tips")))
add.simmap.legend(x=obj$x.lim[1],y=obj$y.lim[2],
    colors=setNames(palette()[1:length(states)],states),
    prompt=FALSE)

That's the hack.