Upstreaming bevy_color. (bevyengine#12013)

# Objective

This provides a new set of color types and operations for Bevy.

Fixes: bevyengine#10986 bevyengine#1402 

## Solution

The new crate provides a set of distinct types for various useful color
spaces, along with utilities for manipulating and converting colors.

This is not a breaking change, as no Bevy APIs are modified (yet).

---------

Co-authored-by: François <[email protected]>

crates/bevy_color/Cargo.toml

@@ -0,0 +1,20 @@
+[package]
+name = "bevy_color"
+version = "0.13.0"
+edition = "2021"
+description = "Types for representing and manipulating color values"
+homepage = "https://bevyengine.org"
+repository = "https://github.com/bevyengine/bevy"
+license = "MIT OR Apache-2.0"
+keywords = ["bevy", "color"]
+
+[dependencies]
+bevy_math = { path = "../bevy_math", version = "0.14.0-dev" }
+bevy_reflect = { path = "../bevy_reflect", version = "0.14.0-dev", features = [
+  "bevy",
+] }
+bevy_render = { path = "../bevy_render", version = "0.14.0-dev" }
+serde = "1.0"
+
+[lints]
+workspace = true

crates/bevy_color/crates/gen_tests/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "gen_tests"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[workspace]
+
+[dependencies]
+palette = "0.7.4"

crates/bevy_color/crates/gen_tests/README.md

@@ -0,0 +1,11 @@
+# gen_tests for bevy_color
+
+The purpose of this crate is to generate test data for validating the color conversion
+functions. It is not part of the Bevy library and should only be run by developers
+working on Bevy.
+
+To generate the file:
+
+```sh
+cargo run > ../../src/test_colors.rs
+```

crates/bevy_color/crates/gen_tests/src/main.rs

@@ -0,0 +1,90 @@
+use palette::{Hsl, IntoColor, Lch, LinSrgb, Oklab, Srgb};
+
+const TEST_COLORS: &[(f32, f32, f32, &str)] = &[
+    (0., 0., 0., "black"),
+    (1., 1., 1., "white"),
+    (1., 0., 0., "red"),
+    (0., 1., 0., "green"),
+    (0., 0., 1., "blue"),
+    (1., 1., 0., "yellow"),
+    (1., 0., 1., "magenta"),
+    (0., 1., 1., "cyan"),
+    (0.5, 0.5, 0.5, "gray"),
+    (0.5, 0.5, 0., "olive"),
+    (0.5, 0., 0.5, "purple"),
+    (0., 0.5, 0.5, "teal"),
+    (0.5, 0., 0., "maroon"),
+    (0., 0.5, 0., "lime"),
+    (0., 0., 0.5, "navy"),
+    (0.5, 0.5, 0., "orange"),
+    (0.5, 0., 0.5, "fuchsia"),
+    (0., 0.5, 0.5, "aqua"),
+];
+
+fn main() {
+    println!(
+        "// Generated by gen_tests. Do not edit.
+#[cfg(test)]
+use crate::{{Hsla, Srgba, LinearRgba, Oklaba, Lcha}};
+
+#[cfg(test)]
+pub struct TestColor {{
+    pub name: &'static str,
+    pub rgb: Srgba,
+    pub linear_rgb: LinearRgba,
+    pub hsl: Hsla,
+    pub lch: Lcha,
+    pub oklab: Oklaba,
+}}
+"
+    );
+
+    println!("// Table of equivalent colors in various color spaces");
+    println!("#[cfg(test)]");
+    println!("pub const TEST_COLORS: &[TestColor] = &[");
+    for (r, g, b, name) in TEST_COLORS {
+        let srgb = Srgb::new(*r, *g, *b);
+        let linear_rgb: LinSrgb = srgb.into_color();
+        let hsl: Hsl = srgb.into_color();
+        let lch: Lch = srgb.into_color();
+        let oklab: Oklab = srgb.into_color();
+        println!("    // {name}");
+        println!(
+            "    TestColor {{
+        name: \"{name}\",
+        rgb: Srgba::new({}, {}, {}, 1.0),
+        linear_rgb: LinearRgba::new({}, {}, {}, 1.0),
+        hsl: Hsla::new({}, {}, {}, 1.0),
+        lch: Lcha::new({}, {}, {}, 1.0),
+        oklab: Oklaba::new({}, {}, {}, 1.0),
+    }},",
+            VariablePrecision(srgb.red),
+            VariablePrecision(srgb.green),
+            VariablePrecision(srgb.blue),
+            VariablePrecision(linear_rgb.red),
+            VariablePrecision(linear_rgb.green),
+            VariablePrecision(linear_rgb.blue),
+            VariablePrecision(hsl.hue.into_positive_degrees()),
+            VariablePrecision(hsl.saturation),
+            VariablePrecision(hsl.lightness),
+            VariablePrecision(lch.l / 100.0),
+            VariablePrecision(lch.chroma / 100.0),
+            VariablePrecision(lch.hue.into_positive_degrees()),
+            VariablePrecision(oklab.l),
+            VariablePrecision(oklab.a),
+            VariablePrecision(oklab.b),
+        );
+    }
+    println!("];");
+}
+
+struct VariablePrecision(f32);
+
+impl std::fmt::Display for VariablePrecision {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if self.0.fract() == 0.0 {
+            return write!(f, "{}.0", self.0);
+        }
+        write!(f, "{}", self.0)
+    }
+}

crates/bevy_color/src/color.rs

@@ -0,0 +1,128 @@
+use crate::{Hsla, Lcha, LinearRgba, Oklaba, Srgba};
+
+/// An enumerated type that can represent any of the color 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.
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum Color {
+    /// A color in the sRGB color space with alpha.
+    Srgba(Srgba),
+    /// A color in the linear sRGB color space with alpha.
+    LinearRgba(LinearRgba),
+    /// A color in the HSL color space with alpha.
+    Hsla(Hsla),
+    /// A color in the LCH color space with alpha.
+    Lcha(Lcha),
+    /// A color in the Oklaba color space with alpha.
+    Oklaba(Oklaba),
+}
+
+impl Color {
+    /// Return the color as a linear RGBA color.
+    pub fn linear(&self) -> LinearRgba {
+        match self {
+            Color::Srgba(srgba) => (*srgba).into(),
+            Color::LinearRgba(linear) => *linear,
+            Color::Hsla(hsla) => (*hsla).into(),
+            Color::Lcha(lcha) => (*lcha).into(),
+            Color::Oklaba(oklab) => (*oklab).into(),
+        }
+    }
+}
+
+impl Default for Color {
+    fn default() -> Self {
+        Self::Srgba(Srgba::WHITE)
+    }
+}
+
+impl From<Srgba> for Color {
+    fn from(value: Srgba) -> Self {
+        Self::Srgba(value)
+    }
+}
+
+impl From<LinearRgba> for Color {
+    fn from(value: LinearRgba) -> Self {
+        Self::LinearRgba(value)
+    }
+}
+
+impl From<Hsla> for Color {
+    fn from(value: Hsla) -> Self {
+        Self::Hsla(value)
+    }
+}
+
+impl From<Oklaba> for Color {
+    fn from(value: Oklaba) -> Self {
+        Self::Oklaba(value)
+    }
+}
+
+impl From<Lcha> for Color {
+    fn from(value: Lcha) -> Self {
+        Self::Lcha(value)
+    }
+}
+
+impl From<Color> for Srgba {
+    fn from(value: Color) -> Self {
+        match value {
+            Color::Srgba(srgba) => srgba,
+            Color::LinearRgba(linear) => linear.into(),
+            Color::Hsla(hsla) => hsla.into(),
+            Color::Lcha(lcha) => lcha.into(),
+            Color::Oklaba(oklab) => oklab.into(),
+        }
+    }
+}
+
+impl From<Color> for LinearRgba {
+    fn from(value: Color) -> Self {
+        match value {
+            Color::Srgba(srgba) => srgba.into(),
+            Color::LinearRgba(linear) => linear,
+            Color::Hsla(hsla) => hsla.into(),
+            Color::Lcha(lcha) => lcha.into(),
+            Color::Oklaba(oklab) => oklab.into(),
+        }
+    }
+}
+
+impl From<Color> for Hsla {
+    fn from(value: Color) -> Self {
+        match value {
+            Color::Srgba(srgba) => srgba.into(),
+            Color::LinearRgba(linear) => linear.into(),
+            Color::Hsla(hsla) => hsla,
+            Color::Lcha(lcha) => LinearRgba::from(lcha).into(),
+            Color::Oklaba(oklab) => LinearRgba::from(oklab).into(),
+        }
+    }
+}
+
+impl From<Color> for Lcha {
+    fn from(value: Color) -> Self {
+        match value {
+            Color::Srgba(srgba) => srgba.into(),
+            Color::LinearRgba(linear) => linear.into(),
+            Color::Hsla(hsla) => Srgba::from(hsla).into(),
+            Color::Lcha(lcha) => lcha,
+            Color::Oklaba(oklab) => LinearRgba::from(oklab).into(),
+        }
+    }
+}
+
+impl From<Color> for Oklaba {
+    fn from(value: Color) -> Self {
+        match value {
+            Color::Srgba(srgba) => srgba.into(),
+            Color::LinearRgba(linear) => linear.into(),
+            Color::Hsla(hsla) => Srgba::from(hsla).into(),
+            Color::Lcha(lcha) => LinearRgba::from(lcha).into(),
+            Color::Oklaba(oklab) => oklab,
+        }
+    }
+}

crates/bevy_color/src/color_difference.rs

@@ -0,0 +1,13 @@
+//! Module for calculating distance between two colors in the same color space.
+
+/// Calculate the distance between this and another color as if they were coordinates
+/// in a Euclidean space. Alpha is not considered in the distance calculation.
+pub trait EuclideanDistance: Sized {
+    /// Distance from `self` to `other`.
+    fn distance(&self, other: &Self) -> f32 {
+        self.distance_squared(other).sqrt()
+    }
+
+    /// Distance squared from `self` to `other`.
+    fn distance_squared(&self, other: &Self) -> f32;
+}

crates/bevy_color/src/color_ops.rs

@@ -0,0 +1,50 @@
+/// Methods for changing the luminance of a color. Note that these methods are not
+/// guaranteed to produce consistent results across color spaces,
+/// but will be within a given space.
+pub trait Luminance: Sized {
+    /// Return the luminance of this color (0.0 - 1.0).
+    fn luminance(&self) -> f32;
+
+    /// Return a new version of this color with the given luminance. The resulting color will
+    /// be clamped to the valid range for the color space; for some color spaces, clamping
+    /// may cause the hue or chroma to change.
+    fn with_luminance(&self, value: f32) -> Self;
+
+    /// Return a darker version of this color. The `amount` should be between 0.0 and 1.0.
+    /// The amount represents an absolute decrease in luminance, and is distributive:
+    /// `color.darker(a).darker(b) == color.darker(a + b)`. Colors are clamped to black
+    /// if the amount would cause them to go below black.
+    ///
+    /// For a relative decrease in luminance, you can simply `mix()` with black.
+    fn darker(&self, amount: f32) -> Self;
+
+    /// Return a lighter version of this color. The `amount` should be between 0.0 and 1.0.
+    /// The amount represents an absolute increase in luminance, and is distributive:
+    /// `color.lighter(a).lighter(b) == color.lighter(a + b)`. Colors are clamped to white
+    /// if the amount would cause them to go above white.
+    ///
+    /// For a relative increase in luminance, you can simply `mix()` with white.
+    fn lighter(&self, amount: f32) -> Self;
+}
+
+/// Linear interpolation of two colors within a given color space.
+pub trait Mix: Sized {
+    /// Linearly interpolate between this and another color, by factor.
+    /// Factor should be between 0.0 and 1.0.
+    fn mix(&self, other: &Self, factor: f32) -> Self;
+
+    /// Linearly interpolate between this and another color, by factor, storing the result
+    /// in this color. Factor should be between 0.0 and 1.0.
+    fn mix_assign(&mut self, other: Self, factor: f32) {
+        *self = self.mix(&other, factor);
+    }
+}
+
+/// Methods for manipulating alpha values.
+pub trait Alpha: Sized {
+    /// Return a new version of this color with the given alpha value.
+    fn with_alpha(&self, alpha: f32) -> Self;
+
+    /// Return a the alpha component of this color.
+    fn alpha(&self) -> f32;
+}

crates/bevy_color/src/color_range.rs

@@ -0,0 +1,42 @@
+use std::ops::Range;
+
+use crate::Mix;
+
+/// Represents a range of colors that can be linearly interpolated, defined by a start and
+/// end point which must be in the same color space. It works for any color type that
+/// implements [`Mix`].
+///
+/// This is useful for defining gradients or animated color transitions.
+pub trait ColorRange<T: Mix> {
+    /// Get the color value at the given interpolation factor, which should be between 0.0 (start)
+    /// and 1.0 (end).
+    fn at(&self, factor: f32) -> T;
+}
+
+impl<T: Mix> ColorRange<T> for Range<T> {
+    fn at(&self, factor: f32) -> T {
+        self.start.mix(&self.end, factor)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{LinearRgba, Srgba};
+
+    #[test]
+    fn test_color_range() {
+        let range = Srgba::RED..Srgba::BLUE;
+        assert_eq!(range.at(0.0), Srgba::RED);
+        assert_eq!(range.at(0.5), Srgba::new(0.5, 0.0, 0.5, 1.0));
+        assert_eq!(range.at(1.0), Srgba::BLUE);
+
+        let lred: LinearRgba = Srgba::RED.into();
+        let lblue: LinearRgba = Srgba::BLUE.into();
+
+        let range = lred..lblue;
+        assert_eq!(range.at(0.0), lred);
+        assert_eq!(range.at(0.5), LinearRgba::new(0.5, 0.0, 0.5, 1.0));
+        assert_eq!(range.at(1.0), lblue);
+    }
+}