From 1f3b44e51107dc97ce2bded07b93325e96835744 Mon Sep 17 00:00:00 2001
From: Mischa POSLAWSKY <perl@shiar.org>
Date: Sat, 31 Oct 2015 20:43:02 +0100
Subject: [PATCH] termcol: lay out 256-colour table by h/s/v

---
 Shiar_Sheet/Colour.pm | 10 +++++++++-
 termcol.plp           | 36 +++++++++++++++++++++++++++++++-----
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/Shiar_Sheet/Colour.pm b/Shiar_Sheet/Colour.pm
index 7ea68e9..cedfdfb 100644
--- a/Shiar_Sheet/Colour.pm
+++ b/Shiar_Sheet/Colour.pm
@@ -4,13 +4,15 @@ use strict;
 use warnings;
 use List::Util qw( min max );
 
-our $VERSION = '1.01';
+our $VERSION = '1.02';
 
 # ITU-R recommendation 601 luma co-efficients
 our $kr = .299;
 our $kb = .114;
 our $kg = 1 - $kb - $kr;
 
+my $PI = 2 * atan2 1, 0;
+
 sub new {
 	my $class = shift;
 	my @rgb = @_ >= 3 ? @_ : (map {hex} $_[0] =~ /(..)/g);
@@ -39,6 +41,12 @@ sub luminance {
 	return $r*$kr + $g*$kg + $b*$kb;
 }
 
+sub hue {
+	my ($r, $g, $b) = @{ $_[0] };
+	my $hue = atan2 sqrt(3) * ($g - $b), $r*2 - $g - $b;
+	return ($hue + $PI) / $PI / 2; # 0 .. 1
+}
+
 sub rgb24 {
 	my $str = '';
 	$str .= sprintf '%X', min($_ / 17 + .5, 15) for @{ $_[0] };
diff --git a/termcol.plp b/termcol.plp
index 1e5e287..16b3dfe 100644
--- a/termcol.plp
+++ b/termcol.plp
@@ -28,10 +28,11 @@ print
 
 <div class="section">
 <:
-use Shiar_Sheet::Colour '1.01';
+use Shiar_Sheet::Colour '1.02';
+use List::Util qw( min max );
 
 sub colcell {
-	my $name = shift;
+	my $name = shift or return "<td colspan=3>\n";
 	my $col = Shiar_Sheet::Colour->new(@_);
 	my $minhex = $col->rgb24;
 	my $css     = '#' . $col->rgb48;
@@ -251,15 +252,40 @@ print "</table>\n\n";
 <div class="section">
 <h2>256-colour space</h2>
 <:
+my @colmap;  # saturation => value => hue => colcell
 for my $r (0 .. 5) {
-	print '<table>';
 	for my $g (0 .. 5) {
-		print '<tr>';
 		for my $b (0 .. 5) {
 			my $index = $r*6*6 + $g*6 + $b + 16;
-			print colcell($index, map { $_ && $_*40 + 55 } $r, $g, $b);
+			my @rgb = map { $_ && $_*40 + 55 } $r, $g, $b;
+
+			my $h = Shiar_Sheet::Colour->new(@rgb)->hue * 35;
+			my $v = int(max(@rgb) / 255 * 5);
+			my $s = abs(min(@rgb) - max(@rgb)) / 255 * 7;
+			my $grey = !$s;
+
+			$h-- for grep {$h >= $_} 4, 6, 16, 19, 28, 31;
+			$v = 5 - $v;
+			$s = 7 - $s - $v;
+			$s-- if $s;
+
+			if ($grey) {
+				$h = 30;  # greyscale hue
+				$s -= 2;  # lowest saturation for other hues
+				$v = $s = 0 if $s < 0;  # black at full saturation
+			}
+
+			$colmap[$s][$v][$h] = [$index, @rgb];
 		}
 	}
+}
+
+{
+	print '<table>';
+	for my $h (0 .. 30) {
+		print '<tr>';
+		print colcell(@$_) for map { $_->[$h] } map { @{$_} } @colmap;
+	}
 	print "</table>\n";
 }
 print "\n";
-- 
2.30.0