R/add.alpha.R

In lozalojo/mem: The Moving Epidemic Method

#' Add an alpha value to a colour
#' http://www.magesblog.com/2013/04/how-to-change-alpha-value-of-colours-in.html
#'
#' @keywords internal
#' @importFrom grDevices rgb col2rgb
add.alpha <- function(col, alpha = 1) {
  if (missing(col)) {
    stop("Please provide a vector of colours.")
  }
  apply(
    sapply(col, col2rgb) / 255, 2,
    function(x)
      rgb(x[1], x[2], x[3], alpha = alpha)
  )
}