Simple function to show geological periods on a tree

I have been working on bringing various different visual elements to plotted trees. The idea of this one is to overlay the tree with different eras or geological time periods. The default shows geologic periods, since these are often plotted.

I know this is similar to another function of the package strap (which is nicer in many ways, IMHO); however this function creates a different visualization & permits other eras or geological regimes to also be mapped.

geo.legend<-function(leg=NULL,cols=NULL,alpha=0.2,...){
    if(hasArg(cex)) cex<-list(...)$cex
    else cex<-par()$cex
    if(is.null(cols)){
        cols<-setNames(c(
            rgb(255,242,127,255,maxColorValue=255),
            rgb(255,230,25,255,maxColorValue=255),
            rgb(253,154,82,255,maxColorValue=255),
            rgb(127,198,78,255,maxColorValue=255),
            rgb(52,178,201,255,maxColorValue=255),
            rgb(129,43,146,255,maxColorValue=255),
            rgb(240,64,40,255,maxColorValue=255),
            rgb(103,165,153,255,maxColorValue=255),
            rgb(203,140,55,255,maxColorValue=255),
            rgb(179,225,182,255,maxColorValue=255),
            rgb(0,146,112,255,maxColorValue=255),
            rgb(127,160,86,255,maxColorValue=255),
            rgb(247,67,112,255,maxColorValue=255)),
            c("Quaternary","Neogene","Paleogene",
            "Cretaceous","Jurassic","Triassic",
            "Permian","Carboniferous","Devonian",
            "Silurian","Ordovician","Cambrian",
            "Precambrian"))
    }
    if(is.null(leg)){
        leg<-rbind(c(2.588,0),
            c(23.03,2.588),
            c(66.0,23.03),
            c(145.0,66.0),
            c(201.3,145.0),
            c(252.17,201.3),
            c(298.9,252.17),
            c(358.9,298.9),
            c(419.2,358.9),
            c(443.8,419.2),
            c(485.4,443.8),
            c(541.0,485.4),
            c(4600,541.0))
        rownames(leg)<-c("Quaternary","Neogene","Paleogene",
            "Cretaceous","Jurassic","Triassic",
            "Permian","Carboniferous","Devonian",
            "Silurian","Ordovician","Cambrian",
            "Precambrian")
    }
    cols<-sapply(cols,make.transparent,alpha=alpha)
    obj<-get("last_plot.phylo",envir=.PlotPhyloEnv)
    t.max<-max(obj$x.lim)
    ii<-which(leg[,2]<=t.max)
    leg<-leg[ii,]
    leg[max(ii),1]<-t.max
    y<-c(rep(0,2),rep(par()$usr[4],2))
    for(i in 1:nrow(leg)){
        polygon(c(leg[i,1:2],leg[i,2:1]),y,col=cols[rownames(leg)[i]],
            border=NA)
        lines(x=rep(leg[i,1],2),y=c(0,par()$usr[4]),lty="dotted",
            col="grey")
        lines(x=c(leg[i,1],mean(leg[i,])-0.8*cex*
            get.asp()*strheight(rownames(leg)[i])),
            y=c(0,-1),lty="dotted",col="grey")
        lines(x=c(leg[i,2],mean(leg[i,])+0.8*cex*
            get.asp()*strheight(rownames(leg)[i])),
            y=c(0,-1),lty="dotted",col="grey")
        lines(x=rep(mean(leg[i,])-0.8*cex*
            get.asp()*strheight(rownames(leg)[i]),2),
            y=c(-1,par()$usr[3]),lty="dotted",col="grey")
        lines(x=rep(mean(leg[i,])+0.8*cex*
            get.asp()*strheight(rownames(leg)[i]),2),
            y=c(-1,par()$usr[3]),lty="dotted",col="grey")
        polygon(x=c(leg[i,1],
            mean(leg[i,])-0.8*cex*get.asp()*strheight(rownames(leg)[i]),
            mean(leg[i,])-0.8*cex*get.asp()*strheight(rownames(leg)[i]),
            mean(leg[i,])+0.8*cex*get.asp()*strheight(rownames(leg)[i]),
            mean(leg[i,])+0.8*cex*get.asp()*strheight(rownames(leg)[i]),
            leg[i,2]),y=c(0,-1,par()$usr[3],par()$usr[3],-1,0),
            col=cols[rownames(leg)[i]],border=NA)
        text(x=mean(leg[i,]),y=-1,labels=rownames(leg)[i],srt=90,
            adj=c(1,0.5),cex=cex)
    }
}

## borrowed from mapplots
get.asp<-function(){
    pin<-par("pin")
    usr<-par("usr")
    asp<-(pin[2]/(usr[4]-usr[3]))/(pin[1]/(usr[2]-usr[1]))
    asp
}

Here's a demo:

plotTree(tree,direction="leftwards",ftype="off",xlim=c(400,0),
    ylim=c(-7,26),log="x",lwd=1)
geo.legend(alpha=0.3,cex=1.2)
plotTree(tree,direction="leftwards",ftype="off",xlim=c(400,0),
    ylim=c(-7,26),log="x",lwd=1,add=TRUE)

It's nothing too spectacular, but hopefully I can combine it with some other style features & make it look nice.