Color maths 4 (#12575)

# Objective

- Fixes #12202 

## Solution

- This PR implements componentwise (including alpha) addition,
subtraction and scalar multiplication/division for some color types.
- The mentioned color types are `Laba`, `Oklaba`, `LinearRgba` and
`Xyza` as all of them are either physically or perceptually linear as
mentioned by @alice-i-cecile in the issue.

---

## Changelog

- Scalar mul/div for `LinearRgba` may modify alpha now.

## Migration Guide

- Users of scalar mul/div for `LinearRgba` need to be aware of the
change and maybe use the `.clamp()` methods or manually set the `alpha`
channel.

crates/bevy_color/src/laba.rs

@@ -1,6 +1,6 @@
 use crate::{
-    Alpha, ClampColor, Hsla, Hsva, Hwba, LinearRgba, Luminance, Mix, Oklaba, Srgba, StandardColor,
+    impl_componentwise_point, Alpha, ClampColor, Hsla, Hsva, Hwba, LinearRgba, Luminance, Mix,
-    Xyza,
+    Oklaba, Srgba, StandardColor, Xyza,
 };
 use bevy_reflect::prelude::*;
 use serde::{Deserialize, Serialize};
@@ -25,6 +25,8 @@ pub struct Laba {
 
 impl StandardColor for Laba {}
 
+impl_componentwise_point!(Laba, [lightness, a, b, alpha]);
+
 impl Laba {
     /// Construct a new [`Laba`] color from components.
     ///

crates/bevy_color/src/lib.rs

@@ -65,6 +65,12 @@
 //! types in this crate. This is useful when you need to store a color in a data structure
 //! that can't be generic over the color type.
 //!
+//! Color types that are either physically or perceptually linear also implement `Add<Self>`, `Sub<Self>`, `Mul<f32>` and `Div<f32>`
+//! allowing you to use them with splines.
+//!
+//! Please note that most often adding or subtracting colors is not what you may want.
+//! Please have a look at other operations like blending, lightening or mixing colors using e.g. [`Mix`] or [`Luminance`] instead.
+//!
 //! # Example
 //!
 //! ```
@@ -151,3 +157,61 @@ where
     Self: Alpha,
 {
 }
+
+macro_rules! impl_componentwise_point {
+    ($ty: ident, [$($element: ident),+]) => {
+        impl std::ops::Add<Self> for $ty {
+            type Output = Self;
+
+            fn add(self, rhs: Self) -> Self::Output {
+                Self::Output {
+                    $($element: self.$element + rhs.$element,)+
+                }
+            }
+        }
+
+        impl std::ops::Sub<Self> for $ty {
+            type Output = Self;
+
+            fn sub(self, rhs: Self) -> Self::Output {
+                Self::Output {
+                    $($element: self.$element - rhs.$element,)+
+                }
+            }
+        }
+
+        impl std::ops::Mul<f32> for $ty {
+            type Output = Self;
+
+            fn mul(self, rhs: f32) -> Self::Output {
+                Self::Output {
+                    $($element: self.$element * rhs,)+
+                }
+            }
+        }
+
+        impl std::ops::Mul<$ty> for f32 {
+            type Output = $ty;
+
+            fn mul(self, rhs: $ty) -> Self::Output {
+                Self::Output {
+                    $($element: self * rhs.$element,)+
+                }
+            }
+        }
+
+        impl std::ops::Div<f32> for $ty {
+            type Output = Self;
+
+            fn div(self, rhs: f32) -> Self::Output {
+                Self::Output {
+                    $($element: self.$element / rhs,)+
+                }
+            }
+        }
+
+        impl bevy_math::cubic_splines::Point for $ty {}
+    };
+}
+
+pub(crate) use impl_componentwise_point;

crates/bevy_color/src/linear_rgba.rs

@@ -1,7 +1,6 @@
-use std::ops::{Div, Mul};
-
 use crate::{
-    color_difference::EuclideanDistance, Alpha, ClampColor, Luminance, Mix, StandardColor,
+    color_difference::EuclideanDistance, impl_componentwise_point, Alpha, ClampColor, Luminance,
+    Mix, StandardColor,
 };
 use bevy_math::Vec4;
 use bevy_reflect::prelude::*;
@@ -29,6 +28,8 @@ pub struct LinearRgba {
 
 impl StandardColor for LinearRgba {}
 
+impl_componentwise_point!(LinearRgba, [red, green, blue, alpha]);
+
 impl LinearRgba {
     /// A fully black color with full alpha.
     pub const BLACK: Self = Self {
@@ -299,48 +300,6 @@ impl From<LinearRgba> for wgpu::Color {
     }
 }
 
-/// All color channels are scaled directly,
-/// but alpha is unchanged.
-///
-/// Values are not clamped.
-impl Mul<f32> for LinearRgba {
-    type Output = Self;
-
-    fn mul(self, rhs: f32) -> Self {
-        Self {
-            red: self.red * rhs,
-            green: self.green * rhs,
-            blue: self.blue * rhs,
-            alpha: self.alpha,
-        }
-    }
-}
-
-impl Mul<LinearRgba> for f32 {
-    type Output = LinearRgba;
-
-    fn mul(self, rhs: LinearRgba) -> LinearRgba {
-        rhs * self
-    }
-}
-
-/// All color channels are scaled directly,
-/// but alpha is unchanged.
-///
-/// Values are not clamped.
-impl Div<f32> for LinearRgba {
-    type Output = Self;
-
-    fn div(self, rhs: f32) -> Self {
-        Self {
-            red: self.red / rhs,
-            green: self.green / rhs,
-            blue: self.blue / rhs,
-            alpha: self.alpha,
-        }
-    }
-}
-
 // [`LinearRgba`] is intended to be used with shaders
 // So it's the only color type that implements [`ShaderType`] to make it easier to use inside shaders
 impl encase::ShaderType for LinearRgba {

crates/bevy_color/src/oklaba.rs

@@ -1,6 +1,6 @@
 use crate::{
-    color_difference::EuclideanDistance, Alpha, ClampColor, Hsla, Hsva, Hwba, Lcha, LinearRgba,
+    color_difference::EuclideanDistance, impl_componentwise_point, Alpha, ClampColor, Hsla, Hsva,
-    Luminance, Mix, Srgba, StandardColor, Xyza,
+    Hwba, Lcha, LinearRgba, Luminance, Mix, Srgba, StandardColor, Xyza,
 };
 use bevy_reflect::prelude::*;
 use serde::{Deserialize, Serialize};
@@ -25,6 +25,8 @@ pub struct Oklaba {
 
 impl StandardColor for Oklaba {}
 
+impl_componentwise_point!(Oklaba, [lightness, a, b, alpha]);
+
 impl Oklaba {
     /// Construct a new [`Oklaba`] color from components.
     ///

crates/bevy_color/src/xyza.rs

@@ -1,4 +1,6 @@
-use crate::{Alpha, ClampColor, LinearRgba, Luminance, Mix, StandardColor};
+use crate::{
+    impl_componentwise_point, Alpha, ClampColor, LinearRgba, Luminance, Mix, StandardColor,
+};
 use bevy_reflect::prelude::*;
 use serde::{Deserialize, Serialize};
 
@@ -22,6 +24,8 @@ pub struct Xyza {
 
 impl StandardColor for Xyza {}
 
+impl_componentwise_point!(Xyza, [x, y, z, alpha]);
+
 impl Xyza {
     /// Construct a new [`Xyza`] color from components.
     ///