R/transparent_function.R

In ndphillips/yarrr: A Companion to the e-Book "YaRrr!: The Pirate's Guide to R"

#' transparent function
#'
#' This function takes a standard color as an argument and returns a
#' transparent version of that color
#'
#' @param orig.col The original color to be made transparent. Can be specified as a string or a vector of rgb values
#' @param trans.val A number in the interval [0, 1] indicating how transparent to make the color.
#' @param maxColorValue The maximum color value (only used when orig.col is an rgb vector)
#' @keywords colors
#' @export
#' @examples
#'
#' # Diagram of some examples
#' plot(1,
#'   ylim = c(0, 1), xlim = c(0, 12), bty = "n",
#'   xaxt = "n", yaxt = "n", ylab = "", xlab = "", type = "na"
#' )
#'
#'
#' text(6, .9, "transparent('red', trans.val = x)")
#' points(
#'   x = 1:11, y = rep(.8, 11), pch = 16,
#'   col = transparent("red", seq(0, 1, .1)), cex = 2
#' )
#' text(x = 1:11, y = rep(.85, 11), seq(0, 1, .1))
#'
#' text(6, .7, "transparent('red', trans.val = x)")
#' points(
#'   x = 1:11, y = rep(.6, 11), pch = 16,
#'   col = transparent("blue", seq(0, 1, .1)), cex = 2
#' )
#' text(x = 1:11, y = rep(.65, 11), seq(0, 1, .1))
#'
#' text(6, .5, "transparent('forestgreen', trans.val = x)")
#' points(
#'   x = 1:11, y = rep(.4, 11), pch = 16,
#'   col = transparent("forestgreen", seq(0, 1, .1)), cex = 2
#' )
#' text(x = 1:11, y = rep(.45, 11), seq(0, 1, .1))
#'
#' text(6, .3, "transparent('orchid1', trans.val = x)")
#' points(
#'   x = 1:11, y = rep(.2, 11), pch = 16,
#'   col = transparent("orchid1", seq(0, 1, .1)), cex = 2
#' )
#' text(x = 1:11, y = rep(.25, 11), seq(0, 1, .1))
#'
#'
#' # Scatterplot with transparent colors
#'
#' a.x <- rnorm(100, mean = 0, sd = 1)
#' a.y <- a.x + rnorm(100, mean = 0, sd = 1)
#'
#' par(mfrow = c(3, 3))
#'
#' for (trans.val.i in seq(0, .1, length.out = 9)) {
#'   plot(a.x, a.y,
#'     pch = 16, col = transparent("blue", trans.val.i), cex = 1.5,
#'     xlim = c(-5, 5), ylim = c(-5, 5), xlab = "x", ylab = "y",
#'     main = paste("trans.val = ", round(trans.val.i, 2), sep = "")
#'   )
#' }
transparent <- function(orig.col = "red", trans.val = 1, maxColorValue = 255) {
  n.cols <- length(orig.col)
  orig.col <- col2rgb(orig.col)

  final.col <- rep(NA, n.cols)

  for (i in 1:n.cols) {
    final.col[i] <- rgb(orig.col[1, i], orig.col[2, i], orig.col[3, i],
      alpha = (1 - trans.val) * 255,
      maxColorValue = maxColorValue
    )
  }

  return(final.col)
}