1 files changed, 74 insertions, 0 deletions
diff --git a/colors/contrast.sh b/colors/contrast.sh
new file mode 100755
index 0000000..36f4f4e
--- /dev/null
+++ b/colors/contrast.sh
@@ -0,0 +1,74 @@
+#!/bin/sh
+. ./ansi.sh
+. ./colors.sh
+
+lightness() {
+	bc -l <<-EOF
+	define pow(a, b) {
+		if (scale(b) == 0) return a ^ b
+		return e(b * l(a))
+	}
+	define cprime(c) {
+		c = c/256
+		if (c <= 0.03928) return(c / 12.92)
+		return pow((c + 0.055)/1.055, 2.4)
+	}
+	define lumi(r, g, b) {
+		return (cprime(r) * 0.2126) + \
+			(cprime(g) * 0.7152) + \
+			(cprime(b) * 0.0722)
+	}
+	lumi($1, $2, $3)
+	EOF
+}
+contrast() {
+	bc <<-EOF
+	scale = 2
+	define contrast(a, b) {
+		if (a > b) {
+			return (a + 0.05) / (b + 0.05)
+		} else {
+			return (b + 0.05) / (a + 0.05)
+		}
+	}
+	contrast($(lightness $(coldec $1)), $(lightness $(coldec $2)))
+	EOF
+}
+
+[ $# -lt 0 ] || set -- \
+	red   green   yellow   blue   magenta   cyan   white \
+	brred brgreen bryellow brblue brmagenta brcyan brwhite
+
+# lower: error if below this
+lower=4
+# higher: warn if below this
+higher=7
+
+reprint() {
+	printf '%s%s' "$@" "$(reset)"
+}
+
+demo() {
+	reprint "$(fgc $1)$(bgc $2)  demo text  "
+}
+
+gt() {
+	test -n "$(printf 'if (%s > %s) 1' "$1" "$2" | bc)"
+}
+
+for i; do
+	color=$(eval echo '$'$i)
+	value=$(contrast $background $color)
+	if gt "$lower" "$value"; then
+		# fail
+		reprint "$(acol 31)fail"
+	elif gt "$higher" "$value"; then
+		# warn
+		reprint "$(acol 33)warn"
+	else
+		# pass
+		reprint "$(acol 32)pass"
+	fi
+	printf ': #%s at %s\t%s (%s)\n' \
+		"$color" "$value" "$(demo $color $background)" "$i"
+done