R/aveytoolkit_makeTransparent.R

In stefanavey/aveytoolkit: Toolkit of Helper Functions

##' makeTransparent
##'
##' Simple function to make some colors transparent
##'
##' @param ... vector or list of colors
##' @param alpha transparency factor in range [0,1]
##' @return a vector of new colors made transparent
##' @author Ricardo Oliveros-Ramos
##' @keywords aveytoolkit
##' @seealso \code{\link{rgb}}, \code{\link{col2rgb}}
##' @references \url{http://stackoverflow.com/questions/8047668/transparent-equivalent-of-given-color}
##' @export
##' @examples
##' makeTransparent("red", "blue")
##' ##[1] "#FF00007F" "#0000FF7F"
##' makeTransparent("red", "blue", alpha=0.8)
##' ## [1] "#FF0000CC" "#0000FFCC"
makeTransparent <- function(alpha=0.5, ...) {
  if(alpha<0 || alpha>1) stop("alpha must be between 0 and 1")
  alpha = floor(255*alpha)
  newColor = col2rgb(col=unlist(list(...)), alpha=FALSE)
  
  .makeTransparent = function(col, alpha) {
    rgb(red=col[1], green=col[2], blue=col[3], alpha=alpha, maxColorValue=255)
  }

  newColor = apply(newColor, 2, .makeTransparent, alpha=alpha)
  return(newColor)
}