viridis.R

viridis <- function(n, alpha = 1, begin = 0, end = 1, direction = 1, option = "D") {
  if (begin < 0 | begin > 1 | end < 0 | end > 1) {
    stop("begin and end must be in [0,1]")
  }
  if (abs(direction) != 1) {
    stop("direction must be 1 or -1")
  }
  if (direction == -1) {
    tmp <- begin
    begin <- end
    end <- tmp
  }
  option <- switch(EXPR = option, A = "A", magma = "A",
                   B = "B", inferno = "B", C = "C", plasma = "C",
                   D = "D", viridis = "D", E = "E", cividis = "E", {
                     warning(paste0("Option '", option, "' does not exist. Defaulting to 'viridis'."))
                     "D"
                   })
  map <- viridisLite::viridis.map[viridisLite::viridis.map$opt ==
                                    option, ]
  map_cols <- grDevices::rgb(map$R, map$G, map$B)
  fn_cols <- grDevices::colorRamp(map_cols, space = "Lab",
                                  interpolate = "spline")
  cols <- fn_cols(seq(begin, end, length.out = n)) / 255
  grDevices::rgb(cols[, 1], cols[, 2], cols[, 3], alpha = alpha)
}