Better palette generation algorithm

2 files changed, 80 insertions, 55 deletions

diff --git a/src/_functions.scss b/src/_functions.scss
index 9425413..73a1ec9 100644
--- a/src/_functions.scss
+++ b/src/_functions.scss
@@ -1,4 +1,7 @@
+@use 'sass:math';
 @use 'iro-sass/src/index' as iro;
+@use '@oddbird/blend';
+@use '@oddbird/blend/sass/convert' as blend-convert;
 
 @function color($key, $tree: 'colors', $default: null, $global: false) {
     @return iro.props-get(join(--colors, $key), $tree, $default, $global);
@@ -59,3 +62,45 @@
         }
     }
 }
+
+@function multi-contrast($base-color, $colors, $wanted-contrasts) {
+    $dir:      if(lightness($base-color) >= 50%, -1, 1);
+    $base-lum: nth(blend-convert.lin_sRGB_to_XYZ(blend-convert.lin_sRGB(blend-convert.sassToRgb($base-color))), 2) + .05;
+
+    $result:     ();
+    $colors-len: length($colors);
+    $colors-idx: if($dir == -1, $colors-len, 1);
+    $wanted-len: length($wanted-contrasts);
+    $wanted-idx: 1;
+
+    @while $colors-idx >= 1 and $colors-idx <= $colors-len and $wanted-idx <= $wanted-len {
+        $color:    nth($colors, $colors-idx);
+        $lum:      nth(blend-convert.lin_sRGB_to_XYZ(blend-convert.lin_sRGB(blend-convert.sassToRgb($color))), 2) + .05;
+        $contrast: math.div(math.max($base-lum, $lum), math.min($lum, $base-lum));
+
+        @if $contrast != 1 {
+            $contrast: $dir * $contrast;
+
+            @if $lum <= $base-lum {
+                $contrast: -1 * $contrast;
+            }
+        }
+
+        $wanted-contrast: nth($wanted-contrasts, $wanted-idx);
+
+        @if $contrast >= $wanted-contrast {
+            $result:     append($result, $color);
+            $wanted-idx: $wanted-idx + 1;
+        } @else {
+            $colors-idx: $colors-idx + $dir * 1;
+        }
+    }
+
+    $last-color: nth($colors, if($dir == -1, 1, $colors-len));
+
+    @for $i from $wanted-idx through $wanted-len {
+        $result: append($result, $last-color);
+    }
+
+    @return $result;
+}
diff --git a/src/_vars.scss b/src/_vars.scss
index cafdb3d..569d535 100644
--- a/src/_vars.scss
+++ b/src/_vars.scss
@@ -1,4 +1,4 @@
-@use 'sass:math';
+@use 'sass:map';
 @use 'iro-sass/src/index' as iro;
 @use 'include-media/dist/include-media' as media;
 @use '@oddbird/blend';
@@ -21,37 +21,45 @@ media.$unit-intervals: (
 $grays: ();
 
 @for $i from 0 through 100 {
-    $grays: append($grays, $i * 1%);
+    $grays: append($grays, blend.lch($i * 1% 0 0));
 }
 
-$grays-rev: iro.fn-list-reverse($grays);
-
-@function find-gray($lightness, $contrast) {
-    $base: blend.lch($lightness 0 0);
-    $dir:  if($contrast < 0, -1, 1) * if($lightness >= 50%, 1, -1);
-    $args: ();
-
-    @if $dir == 1 {
-        @each $gray in $grays-rev {
-            @if $gray < $lightness {
-                $args: append($args, blend.lch($gray 0 0));
-            }
-        }
-    } @else {
-        @each $gray in $grays {
-            @if $gray > $lightness {
-                $args: append($args, blend.lch($gray 0 0));
-            }
-        }
-    }
+$wanted-grays: (
+    -1.1,
+    -1.05,
+    1,
+    1.15,
+    1.37,
+    1.73,
+    2.4,
+    3.26,
+    7.14,
+    11,
+    17.4,
+);
+
+@function accent-palette($base, $dir: 1) {
+    @return (
+        --hi:        blend.scale($base, $lightness: $dir * 15%, $chroma: $dir * 10%),
+        --main:      $base,
+        --lo:        blend.scale($base, $lightness: $dir * -15%, $chroma: $dir * -10%),
+        --lo2:       blend.scale($base, $lightness: $dir * -25%, $chroma: $dir * -20%),
+        --semi:      rgba($base, .4),
+        --selection: rgba($base, .99),
+        --fg:        blend.contrast($base, #fff, #000),
+    );
+}
+
+@function gray-palette($lightness) {
+    $colors: fn.multi-contrast(blend.lch($lightness * 1% 0 0), $grays, $wanted-grays);
+
+    $palette: ();
 
-    @if length($args) == 0 {
-        @return $base;
+    @for $i from 1 through length($colors) {
+        $palette: map.set($palette, --gray#{$i}, hsl(fn.color(--gray-h), fn.color(--gray-s), lightness(nth($colors, $i))));
     }
 
-    $args: append($args, math.abs($contrast));
-    $result: blend.contrast($base, $args...);
-    @return hsl(fn.color(--gray-h), fn.color(--gray-s), lightness($result));
+    @return $palette;
 }
 
 //
@@ -120,34 +128,6 @@ $grays-rev: iro.fn-list-reverse($grays);
 
 //
 
-@function accent-palette($base, $dir: 1) {
-    @return (
-        --hi:        blend.scale($base, $lightness: $dir * 15%, $chroma: $dir * 10%),
-        --main:      $base,
-        --lo:        blend.scale($base, $lightness: $dir * -15%, $chroma: $dir * -10%),
-        --lo2:       blend.scale($base, $lightness: $dir * -25%, $chroma: $dir * -20%),
-        --semi:      rgba($base, .4),
-        --selection: rgba($base, .99),
-        --fg:        blend.contrast($base, #fff, #000),
-    );
-}
-
-@function gray-palette($lightness) {
-    @return (
-        --gray1:  find-gray($lightness, -1.1),
-        --gray2:  find-gray($lightness, -1.05),
-        --gray3:  find-gray($lightness, 1),
-        --gray4:  find-gray($lightness, 1.15),
-        --gray5:  find-gray($lightness, 1.37),
-        --gray6:  find-gray($lightness, 1.73),
-        --gray7:  find-gray($lightness, 2.4),
-        --gray8:  find-gray($lightness, 3.26),
-        --gray9:  find-gray($lightness, 7.14),
-        --gray10: find-gray($lightness, 11),
-        --gray11: find-gray($lightness, 17.4),
-    );
-}
-
 @include iro.fn-execute {
     @include iro.props-store((
         --colors: (