Replace set_text_color()

Uses the algorithm mentioned at https://stackoverflow.com/a/3943023/2022615 based on the luminance of the background color to determine black or white text. The threshold favored black text in a way that didn't look good with our plots, so I increased the threshold from 0.179 to 0.333.

DESCRIPTION

@@ -29,7 +29,8 @@ Imports:
 Suggests: 
     knitr,
     roxygen2,
-    viridis
+    viridis,
+    testthat
 VignetteBuilder: 
     knitr
 Encoding: UTF-8

R/plot_helpers.R

@@ -1,7 +1,3 @@
-
-
-set_text_color <- function(a) ifelse(apply(col2rgb(a), 2, mean) > 127, "black", "white")
-
 #' Animates a plot
 #'
 #' @param d a preprocessed dataset

R/utils.R

@@ -0,0 +1,13 @@
+set_text_color <- function(x, black = "#000000", white = "#FFFFFF") {
+  # x = color_hex
+  color_rgb <- col2rgb(x)
+  # modified from https://stackoverflow.com/a/3943023/2022615
+  # following W3 guidelines: https://www.w3.org/TR/WCAG20/#relativeluminancedef
+  color_rgb <- color_rgb / 255
+  color_rgb[color_rgb <= 0.03928] <- color_rgb[color_rgb <= 0.03928]/12.92
+  color_rgb[color_rgb  > 0.03928] <- ((color_rgb[color_rgb > 0.03928] + 0.055)/1.055)^2.4
+  lum <- t(color_rgb) %*% c(0.2126, 0.7152, 0.0722)
+  lum <- lum[,1]
+  # threshold is supposed to be 0.179 but 1/3 seems to work better for our plots
+  ifelse(lum > 1/3, black, white)
+}

tests/testthat.R

@@ -0,0 +1,4 @@
+library(testthat)
+library(tidyverbs)
+
+test_check("tidyverbs")

tests/testthat/test-set_text_color.R

@@ -0,0 +1,7 @@
+context("test-set_text_color")
+
+test_that("correct color selection", {
+  colors <- c("#FFFFFF", "#9E788C", "#B679E5", "#4BB757",
+              "#000000", "#0027D8", "#E6071B", "#495B3F")
+  expect_equal(set_text_color(colors), c(rep("#000000", 4), rep("#FFFFFF", 4)))
+})