R/gpl.R

In swatches: Read, Inspect, and Manipulate Color Swatch Files

#' Read colors from GIMP Palette (GPL) files
#'
#' Given a path or URL to an \code{.gpl} file, this function will return
#' a named character vector (if color names are present) of hex RGB colors.
#'
#' @param path partial or full file path or URL to a GPL file
#' @param use_names add color names to the vector (defaults to \code{TRUE}). See NOTE
#' @param .verbose show extra information about GPL file processing
#' @note When using named color palettes in a \code{ggplot2} \code{scale_} context, you
#'     must \code{unname}, set \code{use_names} to \code{FALSE} or override their names
#'     to map to your own factor levels. Also, Neither Lab nor greyscale colors are supported.
#' @export
#' @examples
#' # built-in palette
#' gimp16 <- read_gpl(system.file("palettes", "base16.gpl", package="swatches"))
#' print(gimp16)
#' show_palette(gimp16)
#'
#' # from the internet directly
#' \dontrun{
#  URL <- https://raw.githubusercontent.com/chriskempson/base16-gimp-palette/master/base16-bright.gpl"
#' bright <- read_gpl(URL)
#' print(bright)
#' show_palette(bright)
#' }
read_gpl <- function(path, use_names=TRUE, .verbose=FALSE) {

  if (is_url(path)) {
    tf <- tempfile()
    httr::stop_for_status(httr::GET(path, httr::write_disk(tf)))
    path <- tf
    on.exit(unlink(tf), add = TRUE)
  }

  path <- normalizePath(path.expand(path))

  gpl <- readLines(path, warn=FALSE)

  p_name <- gsub("Name:\ +", "", gpl[2])
  n_colors <- gsub("Columns:\ +", "", gpl[3])

  if (.verbose) {
    message("GPL Palette Name: ", p_name)
    message("# Colors: " , n_colors)
  }

  pal <- NULL

  pal <- sapply(5:length(gpl), function(i) {
    mat <- str_match(gpl[i],
"[[:blank:]]*([[:digit:]]+)[[:blank:]]*([[:digit:]]+)[[:blank:]]*([[:digit:]]+)[[:blank:]]*(.*)$")
    rgb(mat[2], mat[3], mat[4], names=mat[5], maxColorValue=255)
  })

  if (!use_names) { pal <- unname(pal) }

  gsub(" ", "0", pal)

}