Update colour and/or pattern transparency — update

update_alpha() modifies the transparency of colours and/or patterns.

Usage

update_alpha(fill, alpha)

Arguments

fill: A fill colour given as a character or integer vector, or as a (list of) <GridPattern> object(s) and/or colour(s).
alpha: A transparency value between 0 (transparent) and 1 (opaque), parallel to fill.

Value

A character vector of colours or list of <GridPattern> objects.

Details

This is a fork of pattern utilities mainly added to {ggplot2} by Teun van den Brand.
update_alpha() does not depend on {ggplot2} or {scales}.
Like ggplot2::fill_alpha() but unlike scales::alpha() it also attempts to set the transparency of <GridPattern> objects.
Unlike ggplot2::fill_alpha() it will work on a list of length one containing a vector of color strings.

Usage in other packages

To avoid taking a dependency on gridpattern you may copy the source of update_alpha() into your own package under the permissive MIT license. Either use usethis::use_standalone("trevorld/gridpattern", "standalone-update_alpha.R") or copy the file update_alpha.R into your R directory and add grDevices, grid, and rlang to the Imports of your DESCRIPTION file.

Examples

# Typical color input
update_alpha("red", 0.5)
#> [1] "#FF000080"

# Pattern input
if (getRversion() >= "4.2" && requireNamespace("grid", quietly = TRUE)) {
  update_alpha(list(grid::linearGradient()), 0.5)
}
#> [[1]]
#> $x1
#> [1] 0npc
#> 
#> $y1
#> [1] 0npc
#> 
#> $x2
#> [1] 1npc
#> 
#> $y2
#> [1] 1npc
#> 
#> $stops
#> [1] 0 1
#> 
#> $colours
#> [1] "#00000080" "#FFFFFF80"
#> 
#> $extend
#> [1] "pad"
#> 
#> $group
#> [1] TRUE
#> 
#> attr(,"class")
#> [1] "GridLinearGradient" "GridPattern"       
#>