From 72b975ec82660b39f27b6cb015b763caf20e6483 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?H=C3=A9ctor=20Ram=C3=B3n=20Jim=C3=A9nez?= <hector@hecrj.dev>
Date: Sun, 7 Apr 2024 19:37:35 +0200
Subject: [PATCH] Pick best contrast between black/white in `theme::palette`

---
 core/src/theme/palette.rs | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/core/src/theme/palette.rs b/core/src/theme/palette.rs
index aca72eb0c6..e0ff397ab0 100644
--- a/core/src/theme/palette.rs
+++ b/core/src/theme/palette.rs
@@ -4,7 +4,7 @@ use crate::{color, Color};
 use once_cell::sync::Lazy;
 use palette::color_difference::Wcag21RelativeContrast;
 use palette::rgb::Rgb;
-use palette::{FromColor, Hsl, Lch, Mix};
+use palette::{FromColor, Hsl, Mix};
 
 /// A color palette.
 #[derive(Debug, Clone, Copy, PartialEq)]
@@ -613,10 +613,15 @@ fn mix(a: Color, b: Color, factor: f32) -> Color {
 fn readable(background: Color, text: Color) -> Color {
     if is_readable(background, text) {
         text
-    } else if to_lch(background).l < 70.0 {
-        Color::WHITE
     } else {
-        Color::BLACK
+        let white_contrast = relative_contrast(background, Color::WHITE);
+        let black_contrast = relative_contrast(background, Color::BLACK);
+
+        if white_contrast >= black_contrast {
+            Color::WHITE
+        } else {
+            Color::BLACK
+        }
     }
 }
 
@@ -631,12 +636,15 @@ fn is_readable(a: Color, b: Color) -> bool {
     a_srgb.has_enhanced_contrast_text(b_srgb)
 }
 
-fn to_hsl(color: Color) -> Hsl {
-    Hsl::from_color(Rgb::from(color))
+fn relative_contrast(a: Color, b: Color) -> f32 {
+    let a_srgb = Rgb::from(a);
+    let b_srgb = Rgb::from(b);
+
+    a_srgb.relative_contrast(b_srgb)
 }
 
-fn to_lch(color: Color) -> Lch {
-    Lch::from_color(Rgb::from(color))
+fn to_hsl(color: Color) -> Hsl {
+    Hsl::from_color(Rgb::from(color))
 }
 
 fn from_hsl(hsl: Hsl) -> Color {