colour conversions

[SymbolixAU]

TODO

• hex_to_rgb - with and without alpha, both RGB(A) and RRGGBB(AA)
• rgb_to_hex - with and without alpha, allow vectors & matrix inputs

[SymbolixAU]

new convert_hex_to_rgb() benchmarks well

col <- "#00FF00FF"
col <- rep(col, 1e6)

library(microbenchmark)

microbenchmark(
  cv = { colourvalues:::rcpp_convert_hex_to_rgb_new( col) },
  cv_old = { colourvalues:::rcpp_convert_hex_to_rgb( col ) }, 
  gr = { grDevices::col2rgb(col, alpha = TRUE) },
  times = 10
)

# Unit: milliseconds
#   expr       min        lq     mean    median        uq       max neval
#     cv  30.81213  32.73352  47.4408  35.59811  76.95149  81.37984    10
# cv_old 272.52093 276.65413 290.7468 285.09019 295.67034 327.61521    10
#     gr  36.80980  39.10075  41.6736  41.57528  44.91530  46.51591    10

[SymbolixAU]

and the other way

rgb2hex <- function(m) grDevices::rgb(m[,1], m[,2], m[,3], m[,4], maxColorValue = 255)

m <- matrix(c(255,170,0,255),ncol = 4)
n <- 1e6
m <- m[rep(1,n),]

r <- rep(255, n)
g <- rep(170, n)
b <- rep(0, n)
a <- rep(255, n)
microbenchmark(
  gr = { rgb2hex(m) },
  gr2 = { rgb(r,g,b,a, maxColorValue = 255) },
  cv = { colourvalues:::rcpp_convert_rgb_to_hex(m) },
  times = 10
)

# Unit: milliseconds
# expr      min       lq      mean    median        uq       max neval
#  gr 92.93735 97.36313 105.60413 100.61244 104.47904 152.06389    10
# gr2 77.65241 80.03476  93.30192  85.64504  90.76205 131.98374    10
#  cv 78.46464 78.81009  83.86777  81.85836  87.48609  94.67922    10