1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
|
# ---------------------------------------
# Author: Andreas Alfons
# Vienna University of Technology
# ---------------------------------------
#' Alphablending for colors
#'
#' Convert colors to semitransparent colors.
#'
#'
#' @param col a vector specifying colors.
#' @param alpha a numeric vector containing the alpha values (between 0 and 1).
#' @param bg the background color to be used for alphablending. This can be
#' used as a workaround for graphics devices that do not support
#' semitransparent colors.
#' @return a vector containing the semitransparent colors.
#' @author Andreas Alfons
#' @keywords color
#' @examples
#'
#' alphablend("red", 0.6)
#'
#' @export alphablend
alphablend <- function(col, alpha = NULL, bg = NULL) {
if(length(alpha) == 0) col
else {
alpha <- rep(alpha, length.out=length(col))
if(length(bg) == 0) {
colrgb <- col2rgb(col)/255
rgb(colrgb[1,], colrgb[2,], colrgb[3,], alpha)
} else {
if(any(alpha < 0 | alpha > 1)) {
stop("values in 'alpha' must be between 0 and 1")
}
colrgb <- col2rgb(col)/255
bgrgb <- as.vector(col2rgb(bg[1])/255)
red <- alpha*colrgb[1,] + (1-alpha)*bgrgb[1]
green <- alpha*colrgb[2,] + (1-alpha)*bgrgb[2]
blue <- alpha*colrgb[3,] + (1-alpha)*bgrgb[3]
mapply(rgb, red, green, blue)
}
}
}
|
