Add conversions from Color to u32 (bevyengine#4088)

# Objective

- `Mesh::ATTRIBUTE_COLOR` expects colors as `u32`s but there is no function for easy conversion.
- See bevyengine#4037 (review)

## Solution

- Added `Color::as_rgba_u32` and `Color::as_linear_rgba_u32`

crates/bevy_render/src/color/mod.rs

@@ -414,7 +414,7 @@ impl Color {
  }
  }
 
- /// Converts a `Color` to a `[f32; 4]` from linear RBG colorspace
+ /// Converts a `Color` to a `[f32; 4]` from linear RGB colorspace
  #[inline]
  pub fn as_linear_rgba_f32(self: Color) -> [f32; 4] {
  match self {
@@ -487,6 +487,98 @@ impl Color {
  } => [hue, saturation, lightness, alpha],
  }
  }
+
+ /// Converts Color to a u32 from sRGB colorspace.
+ ///
+ /// Maps the RGBA channels in RGBA order to a little-endian byte array (GPUs are little-endian).
+ /// A will be the most significant byte and R the least significant.
+ pub fn as_rgba_u32(self: Color) -> u32 {
+ match self {
+ Color::Rgba {
+ red,
+ green,
+ blue,
+ alpha,
+ } => u32::from_le_bytes([
+ (red * 255.0) as u8,
+ (green * 255.0) as u8,
+ (blue * 255.0) as u8,
+ (alpha * 255.0) as u8,
+ ]),
+ Color::RgbaLinear {
+ red,
+ green,
+ blue,
+ alpha,
+ } => u32::from_le_bytes([
+ (red.linear_to_nonlinear_srgb() * 255.0) as u8,
+ (green.linear_to_nonlinear_srgb() * 255.0) as u8,
+ (blue.linear_to_nonlinear_srgb() * 255.0) as u8,
+ (alpha * 255.0) as u8,
+ ]),
+ Color::Hsla {
+ hue,
+ saturation,
+ lightness,
+ alpha,
+ } => {
+ let [red, green, blue] =
+ HslRepresentation::hsl_to_nonlinear_srgb(hue, saturation, lightness);
+ u32::from_le_bytes([
+ (red * 255.0) as u8,
+ (green * 255.0) as u8,
+ (blue * 255.0) as u8,
+ (alpha * 255.0) as u8,
+ ])
+ }
+ }
+ }
+
+ /// Converts Color to a u32 from linear RGB colorspace.
+ ///
+ /// Maps the RGBA channels in RGBA order to a little-endian byte array (GPUs are little-endian).
+ /// A will be the most significant byte and R the least significant.
+ pub fn as_linear_rgba_u32(self: Color) -> u32 {
+ match self {
+ Color::Rgba {
+ red,
+ green,
+ blue,
+ alpha,
+ } => u32::from_le_bytes([
+ (red.nonlinear_to_linear_srgb() * 255.0) as u8,
+ (green.nonlinear_to_linear_srgb() * 255.0) as u8,
+ (blue.nonlinear_to_linear_srgb() * 255.0) as u8,
+ (alpha * 255.0) as u8,
+ ]),
+ Color::RgbaLinear {
+ red,
+ green,
+ blue,
+ alpha,
+ } => u32::from_le_bytes([
+ (red * 255.0) as u8,
+ (green * 255.0) as u8,
+ (blue * 255.0) as u8,
+ (alpha * 255.0) as u8,
+ ]),
+ Color::Hsla {
+ hue,
+ saturation,
+ lightness,
+ alpha,
+ } => {
+ let [red, green, blue] =
+ HslRepresentation::hsl_to_nonlinear_srgb(hue, saturation, lightness);
+ u32::from_le_bytes([
+ (red.nonlinear_to_linear_srgb() * 255.0) as u8,
+ (green.nonlinear_to_linear_srgb() * 255.0) as u8,
+ (blue.nonlinear_to_linear_srgb() * 255.0) as u8,
+ (alpha * 255.0) as u8,
+ ])
+ }
+ }
+ }
 }
 
 impl Default for Color {