cprop <- function(x) {
    prop <- x/sum(x)
    cumsum(prop)
}


prop <- function(x) {
    x/sum(x)
}


spine <- function(x) {
    px <- prop(x)
    cpx <- cprop(x)
    grid.rect(y=cpx, height=px, just="top")
}


connector <- function(x1, x2) {
    cp1 <- cprop(x1)
    cp2 <- cprop(x2)
    grid.segments(0, cp1, 1, cp2)
}