R/make_transparent.R

In mjdufort/miscHelpers: Miscellaneous helper functions

#' Add transparency to a vector of colors
#'
#' Add a transparency factor to each color in a vector of color names, using alpha on a scale of 0-255. Adapted from http://stackoverflow.com/questions/8047668/transparent-equivalent-of-given-color.
#' @param color_names vector of color names to be modified.
#' @param alpha numeric, the alpha value, between 0 (completely transparent) and 255 (the original color). Passed to \code{rgb}.
#' @importFrom grDevices col2rgb
#' @export
#' @return a character vector of the same length as \code{color_names}
#' @usage make_transparent(color_names, alpha = 100)
make_transparent <- function(color_names, alpha = 100) {
  new_colors <- col2rgb(color_names)
  apply(new_colors, 2,
        function(x) {
          rgb(red = x[1], green = x[2], blue = x[3],
              alpha = alpha, maxColorValue = 255)
          })
}