add relative_luminance() and contrast_ratio() to Color

Zentiph · Zentiph · commit 033fb8b867ac · 2025-10-28T20:52:21.000-04:00
diff --git a/src/color/lut.rs b/src/color/lut.rs
@@ -5,8 +5,6 @@
 
 #![allow(dead_code)]
 
-// Compile-time params
-
 use std::sync::OnceLock;
 
 /// linear -> sRGB table size
diff --git a/src/color/model.rs b/src/color/model.rs
@@ -178,6 +178,24 @@ impl Color {
         dst
     }
 
+    #[must_use]
+    #[inline]
+    pub fn relative_luminance(self) -> f32 {
+        let [r, g, b, _] = self.into_linear::<f32>();
+        0.2126 * r + 0.7152 * g + 0.0722 * b
+    }
+
+    #[must_use]
+    #[inline]
+    pub fn contrast_ratio(self, other: Color) -> f32 {
+        let (l1, l2) = {
+            let a = self.relative_luminance();
+            let b = other.relative_luminance();
+            if a >= b { (a, b) } else { (b, a) }
+        };
+        (l1 + 0.05) / (l2 + 0.05)
+    }
+
     #[must_use]
     #[inline]
     pub fn with_alpha(self, a: u8) -> Self {
@@ -233,6 +251,8 @@ impl Color {
         format!("{:02x}{:02x}{:02x}{:02x}", self.r, self.g, self.b, self.a)
     }
 
+    // TODO make rest of the f32/f64 funcs generic with Float
+
     #[must_use]
     #[inline]
     pub fn from_hsl_f32(hsl: [f32; 3]) -> Self {
