store color in linear

src/layout/color.rs

@@ -1,5 +1,6 @@
 #![allow(clippy::multiple_bound_locations)]
 
+/// stored in linear for sane manipulation
 #[repr(C)]
 #[derive(Clone, Copy, bytemuck::Zeroable, Debug)]
 pub struct Color<T: ColorNum> {
@@ -63,6 +64,7 @@ impl ColorNum for f32 {
 
 unsafe impl bytemuck::Pod for Color<u8> {}
 
+#[const_trait]
 pub trait F32Conversion {
     fn to(self) -> f32;
     fn from(x: f32) -> Self;
@@ -87,9 +89,27 @@ impl<T: ColorNum + F32Conversion> Color<T> {
             a: self.a,
         }
     }
+
+    pub fn srgb(r: T, g: T, b: T) -> Self {
+        Self {
+            r: s_to_l(r),
+            g: s_to_l(g),
+            b: s_to_l(b),
+            a: T::MAX,
+        }
+    }
 }
 
-impl F32Conversion for f32 {
+fn s_to_l<T: F32Conversion>(x: T) -> T {
+    let x = x.to();
+    T::from(if x <= 0.0405 {
+        x / 12.92
+    } else {
+        ((x + 0.055) / 1.055).powf(2.4)
+    })
+}
+
+impl const F32Conversion for f32 {
     fn to(self) -> f32 {
         self
     }
@@ -98,7 +118,7 @@ impl F32Conversion for f32 {
     }
 }
 
-impl F32Conversion for u8 {
+impl const F32Conversion for u8 {
     fn to(self) -> f32 {
         self as f32 / 255.0
     }