R/col2transparent.R

In kullrich/CRBHits: Conditional reciprocal best hits (CRBHits) in R

#' @title col2transparent
#' @name col2transparent
#' @description R color to transparent conversion.
#' @param col R color name or R color pal [mandatory]
#' @param alpha.perc an alpha-transparency level in percent [default: 0]
#' @return A character vector with elements of 9 characters,
#' "#" followed by the red, blue, green and alpha values in hexadecimal
#' (after rescaling to 0 ... 255).
#' @importFrom grDevices col2rgb palette rgb
#' @importFrom methods is slot
#' @seealso \code{\link[grDevices]{palette}}
#' @examples
#' col2transparent("green", 50)
#' ## Demonstrate the colors 1:8 in different palettes using a custom matplot()
#' sinplot <- function(main=NULL) {
#'     x <- outer(
#'         seq(-pi, pi, length.out = 50),
#'         seq(0, pi, length.out = 9),
#'         function(x, y) sin(x - y)
#'     )
#'     matplot(x, type = "l", lwd = 4, lty = 1, col = 1:9, ylab = "", main=main)
#' }
#' my.palette <- c(
#'     "#CBC106", "#27993C", "#1C6838",
#'     "#8EBCB5", "#389CA7", "#4D83AB",
#'     "#CB7B26", "#BF565D", "#9E163C")
#' palette(my.palette); sinplot("my.palette")
#' ## 25% transparent
#' palette(col2transparent(palette(my.palette), 25));
#'     sinplot("my.palette - transparent")
#' ## 50% transparent
#' palette(col2transparent(palette(my.palette), 50));
#'     sinplot("my.palette - transparent")
#' ## 75% transparent
#' palette(col2transparent(palette(my.palette), 75));
#'     sinplot("my.palette - transparent")
#' @export col2transparent
#' @author Kristian K Ullrich

col2transparent <- function(col,
    alpha.perc=0
    ){
    if(methods::is(col, "character")){
        if(length(col)==1){
            alpha = (100 - alpha.perc) * 255 / 100
            R = col2rgb(col)[1]
            G = col2rgb(col)[2]
            B = col2rgb(col)[3]
            return(rgb(R, G, B, alpha, maxColorValue=255))
        } else {
            return(unlist(lapply(col,
                function(x) {col2transparent(x, alpha.perc)})))
        }
    }
    if(methods::is(col, "palette")){
        return(palette(unlist(lapply(col,
            function(x) {col2transparent(x, alpha.perc)}))))
    }
}