Add no_std support to bevy_color (#16633)

# Objective

- Contributes to #15460

## Solution

- Added the following new features: 
  - `std` (default)
  - `alloc`
  - `encase` (default)
  - `libm`

## Testing

- Added to `compile-check-no-std` CI command

## Notes

- `ColorCurve` requires `alloc` due to how the underlying `EvenCore`
type works.
- `Srgba::to_hex` requires `alloc` to return a `String`.
- This was otherwise a _very_ simple change

crates/bevy_color/Cargo.toml

@@ -17,18 +17,26 @@ bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", features = [
   "bevy",
 ], optional = true }
 bytemuck = { version = "1", features = ["derive"] }
-serde = { version = "1.0", features = ["derive"], optional = true }
+serde = { version = "1.0", features = [
+  "derive",
+], default-features = false, optional = true }
 derive_more = { version = "1", default-features = false, features = [
   "error",
   "from",
   "display",
 ] }
 wgpu-types = { version = "23", default-features = false, optional = true }
-encase = { version = "0.10", default-features = false }
+encase = { version = "0.10", default-features = false, optional = true }
 
 [features]
-default = ["bevy_reflect"]
+default = ["std", "bevy_reflect", "encase"]
+std = ["alloc", "bevy_math/std", "serde?/std"]
+alloc = ["bevy_math/alloc", "serde?/alloc"]
 serialize = ["serde", "bevy_math/serialize"]
+bevy_reflect = ["dep:bevy_reflect", "std"]
+wgpu-types = ["dep:wgpu-types", "std"]
+encase = ["dep:encase", "std"]
+libm = ["bevy_math/libm"]
 
 [lints]
 workspace = true

crates/bevy_color/src/color_difference.rs

@@ -1,11 +1,13 @@
 //! Module for calculating distance between two colors in the same color space.
 
+use bevy_math::ops;
+
 /// 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()
+        ops::sqrt(self.distance_squared(other))
     }
 
     /// Distance squared from `self` to `other`.

crates/bevy_color/src/color_gradient.rs

@@ -1,4 +1,5 @@
 use crate::Mix;
+use alloc::vec::Vec;
 use bevy_math::curve::{
     cores::{EvenCore, EvenCoreError},
     Curve, Interval,

crates/bevy_color/src/color_ops.rs

@@ -1,4 +1,4 @@
-use bevy_math::{Vec3, Vec4};
+use bevy_math::{ops, Vec3, Vec4};
 
 /// Methods for changing the luminance of a color. Note that these methods are not
 /// guaranteed to produce consistent results across color spaces,
@@ -90,7 +90,7 @@ pub trait Hue: Sized {
 
     /// Return a new version of this color with the hue channel rotated by the given degrees.
     fn rotate_hue(&self, degrees: f32) -> Self {
-        let rotated_hue = (self.hue() + degrees).rem_euclid(360.);
+        let rotated_hue = ops::rem_euclid(self.hue() + degrees, 360.);
         self.with_hue(rotated_hue)
     }
 }
@@ -131,8 +131,8 @@ pub trait ColorToPacked {
 /// takes the shortest path around the color wheel, and that the result is always between
 /// 0 and 360.
 pub(crate) fn lerp_hue(a: f32, b: f32, t: f32) -> f32 {
-    let diff = (b - a + 180.0).rem_euclid(360.) - 180.;
+    let diff = ops::rem_euclid(b - a + 180.0, 360.) - 180.;
-    (a + diff * t).rem_euclid(360.0)
+    ops::rem_euclid(a + diff * t, 360.)
 }
 
 #[cfg(test)]

crates/bevy_color/src/hwba.rs

@@ -5,7 +5,7 @@
 use crate::{
     Alpha, ColorToComponents, Gray, Hue, Lcha, LinearRgba, Mix, Srgba, StandardColor, Xyza,
 };
-use bevy_math::{Vec3, Vec4};
+use bevy_math::{ops, Vec3, Vec4};
 #[cfg(feature = "bevy_reflect")]
 use bevy_reflect::prelude::*;
 
@@ -239,7 +239,7 @@ impl From<Hwba> for Srgba {
         let v = 1. - blackness;
 
         let h = (hue % 360.) / 60.;
-        let i = h.floor();
+        let i = ops::floor(h);
         let f = h - i;
 
         let i = i as u8;

crates/bevy_color/src/lib.rs

@@ -4,6 +4,7 @@
     html_logo_url = "https://bevyengine.org/assets/icon.png",
     html_favicon_url = "https://bevyengine.org/assets/icon.png"
 )]
+#![cfg_attr(not(feature = "std"), no_std)]
 
 //! Representations of colors in various color spaces.
 //!
@@ -89,8 +90,12 @@
 //! println!("Hsla: {:?}", hsla);
 //! ```
 
+#[cfg(feature = "alloc")]
+extern crate alloc;
+
 mod color;
 pub mod color_difference;
+#[cfg(feature = "alloc")]
 mod color_gradient;
 mod color_ops;
 mod color_range;
@@ -121,6 +126,7 @@ pub mod prelude {
 }
 
 pub use color::*;
+#[cfg(feature = "alloc")]
 pub use color_gradient::*;
 pub use color_ops::*;
 pub use color_range::*;

crates/bevy_color/src/linear_rgba.rs

@@ -2,7 +2,7 @@ use crate::{
     color_difference::EuclideanDistance, impl_componentwise_vector_space, Alpha, ColorToComponents,
     ColorToPacked, Gray, Luminance, Mix, StandardColor,
 };
-use bevy_math::{Vec3, Vec4};
+use bevy_math::{ops, Vec3, Vec4};
 #[cfg(feature = "bevy_reflect")]
 use bevy_reflect::prelude::*;
 use bytemuck::{Pod, Zeroable};
@@ -302,11 +302,11 @@ impl ColorToComponents for LinearRgba {
 impl ColorToPacked for LinearRgba {
     fn to_u8_array(self) -> [u8; 4] {
         [self.red, self.green, self.blue, self.alpha]
-            .map(|v| (v.clamp(0.0, 1.0) * 255.0).round() as u8)
+            .map(|v| ops::round(v.clamp(0.0, 1.0) * 255.0) as u8)
     }
 
     fn to_u8_array_no_alpha(self) -> [u8; 3] {
-        [self.red, self.green, self.blue].map(|v| (v.clamp(0.0, 1.0) * 255.0).round() as u8)
+        [self.red, self.green, self.blue].map(|v| ops::round(v.clamp(0.0, 1.0) * 255.0) as u8)
     }
 
     fn from_u8_array(color: [u8; 4]) -> Self {
@@ -332,6 +332,7 @@ impl From<LinearRgba> for wgpu_types::Color {
 
 // [`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
+#[cfg(feature = "encase")]
 impl encase::ShaderType for LinearRgba {
     type ExtraMetadata = ();
 
@@ -353,6 +354,7 @@ impl encase::ShaderType for LinearRgba {
     const UNIFORM_COMPAT_ASSERT: fn() = || {};
 }
 
+#[cfg(feature = "encase")]
 impl encase::private::WriteInto for LinearRgba {
     fn write_into<B: encase::private::BufferMut>(&self, writer: &mut encase::private::Writer<B>) {
         for el in &[self.red, self.green, self.blue, self.alpha] {
@@ -361,6 +363,7 @@ impl encase::private::WriteInto for LinearRgba {
     }
 }
 
+#[cfg(feature = "encase")]
 impl encase::private::ReadFrom for LinearRgba {
     fn read_from<B: encase::private::BufferRef>(
         &mut self,
@@ -380,6 +383,7 @@ impl encase::private::ReadFrom for LinearRgba {
     }
 }
 
+#[cfg(feature = "encase")]
 impl encase::private::CreateFrom for LinearRgba {
     fn create_from<B>(reader: &mut encase::private::Reader<B>) -> Self
     where
@@ -400,6 +404,7 @@ impl encase::private::CreateFrom for LinearRgba {
     }
 }
 
+#[cfg(feature = "encase")]
 impl encase::ShaderSize for LinearRgba {}
 
 #[cfg(test)]

crates/bevy_color/src/srgba.rs

@@ -2,6 +2,8 @@ use crate::{
     color_difference::EuclideanDistance, impl_componentwise_vector_space, Alpha, ColorToComponents,
     ColorToPacked, Gray, LinearRgba, Luminance, Mix, StandardColor, Xyza,
 };
+#[cfg(feature = "alloc")]
+use alloc::{format, string::String};
 use bevy_math::{ops, Vec3, Vec4};
 #[cfg(feature = "bevy_reflect")]
 use bevy_reflect::prelude::*;
@@ -167,6 +169,7 @@ impl Srgba {
     }
 
     /// Convert this color to CSS-style hexadecimal notation.
+    #[cfg(feature = "alloc")]
     pub fn to_hex(&self) -> String {
         let [r, g, b, a] = self.to_u8_array();
         match a {
@@ -366,11 +369,11 @@ impl ColorToComponents for Srgba {
 impl ColorToPacked for Srgba {
     fn to_u8_array(self) -> [u8; 4] {
         [self.red, self.green, self.blue, self.alpha]
-            .map(|v| (v.clamp(0.0, 1.0) * 255.0).round() as u8)
+            .map(|v| ops::round(v.clamp(0.0, 1.0) * 255.0) as u8)
     }
 
     fn to_u8_array_no_alpha(self) -> [u8; 3] {
-        [self.red, self.green, self.blue].map(|v| (v.clamp(0.0, 1.0) * 255.0).round() as u8)
+        [self.red, self.green, self.blue].map(|v| ops::round(v.clamp(0.0, 1.0) * 255.0) as u8)
     }
 
     fn from_u8_array(color: [u8; 4]) -> Self {

tools/ci/src/commands/compile_check_no_std.rs

@@ -86,6 +86,14 @@ impl Prepare for CompileCheckNoStdCommand {
             "Please fix compiler errors in output above for bevy_math no_std compatibility.",
         ));
 
+        commands.push(PreparedCommand::new::<Self>(
+            cmd!(
+                sh,
+                "cargo check -p bevy_color --no-default-features --features libm --target {target}"
+            ),
+            "Please fix compiler errors in output above for bevy_color no_std compatibility.",
+        ));
+
         commands
     }
 }