Better palette generation algorithm

1 files changed, 45 insertions, 0 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;
+}