sRGB awareness for Color (#616)

Color is now sRGB aware, added SrgbColorSpace trait for f32

CHANGELOG.md

@@ -6,7 +6,16 @@
 
 - [Another fast compile flag for macOS][552]
 
+### Changed
+
+- Breaking Change: [sRGB awareness for `Color`][616]
+  - Color is now assumed to be provided in the non-linear sRGB colorspace, and constructors such as `Color::rgb` and `Color::rgba` will be converted to linear sRGB under-the-hood. 
+  - This allows drop-in use of colors from most applications.
+  - New methods `Color::rgb_linear` and `Color::rgba_linear` will accept colors already in linear sRGB (the old behavior)
+  - Individual color-components must now be accessed through setters and getters: `.r`, `.g`, `.b`, `.a`, `.set_r`, `.set_g`, `.set_b`, `.set_a`, and the corresponding methods with the `*_linear` suffix.
+
 [552]: https://github.com/bevyengine/bevy/pull/552
+[616]: https://github.com/bevyengine/bevy/pull/616
 
 ## Version 0.2.1 (2020-9-20)
 

crates/bevy_render/src/color.rs

@@ -1,5 +1,6 @@
 use super::texture::Texture;
 use crate::{
+    colorspace::*,
     impl_render_resource_bytes,
     renderer::{RenderResource, RenderResourceType},
 };
@@ -10,32 +11,68 @@ use bevy_property::Property;
 use serde::{Deserialize, Serialize};
 use std::ops::{Add, AddAssign, Mul, MulAssign};
 
-/// A RGBA color
+/// RGBA color in the Linear sRGB colorspace (often colloquially referred to as "linear", "RGB", or "linear RGB").
 #[repr(C)]
 #[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize, Property)]
 pub struct Color {
-    pub r: f32,
+    red: f32,
-    pub g: f32,
+    green: f32,
-    pub b: f32,
+    blue: f32,
-    pub a: f32,
+    alpha: f32,
 }
 
 unsafe impl Byteable for Color {}
 
 impl Color {
-    pub const BLACK: Color = Color::rgb(0.0, 0.0, 0.0);
+    pub const BLACK: Color = Color::rgb_linear(0.0, 0.0, 0.0);
-    pub const BLUE: Color = Color::rgb(0.0, 0.0, 1.0);
+    pub const BLUE: Color = Color::rgb_linear(0.0, 0.0, 1.0);
-    pub const GREEN: Color = Color::rgb(0.0, 1.0, 0.0);
+    pub const GREEN: Color = Color::rgb_linear(0.0, 1.0, 0.0);
-    pub const NONE: Color = Color::rgba(0.0, 0.0, 0.0, 0.0);
+    pub const NONE: Color = Color::rgba_linear(0.0, 0.0, 0.0, 0.0);
-    pub const RED: Color = Color::rgb(1.0, 0.0, 0.0);
+    pub const RED: Color = Color::rgb_linear(1.0, 0.0, 0.0);
-    pub const WHITE: Color = Color::rgb(1.0, 1.0, 1.0);
+    pub const WHITE: Color = Color::rgb_linear(1.0, 1.0, 1.0);
 
-    pub const fn rgb(r: f32, g: f32, b: f32) -> Color {
+    // TODO: cant make rgb and rgba const due traits not allowed in const functions
-        Color { r, g, b, a: 1.0 }
+    // see issue #57563 https://github.com/rust-lang/rust/issues/57563
+    /// New ``Color`` from sRGB colorspace.
+    pub fn rgb(r: f32, g: f32, b: f32) -> Color {
+        Color {
+            red: r,
+            green: g,
+            blue: b,
+            alpha: 1.0,
+        }
+        .as_nonlinear_srgb_to_linear_srgb()
     }
 
-    pub const fn rgba(r: f32, g: f32, b: f32, a: f32) -> Color {
+    /// New ``Color`` from sRGB colorspace.
-        Color { r, g, b, a }
+    pub fn rgba(r: f32, g: f32, b: f32, a: f32) -> Color {
+        Color {
+            red: r,
+            green: g,
+            blue: b,
+            alpha: a,
+        }
+        .as_nonlinear_srgb_to_linear_srgb()
+    }
+
+    /// New ``Color`` from linear colorspace.
+    pub const fn rgb_linear(r: f32, g: f32, b: f32) -> Color {
+        Color {
+            red: r,
+            green: g,
+            blue: b,
+            alpha: 1.0,
+        }
+    }
+
+    /// New ``Color`` from linear colorspace.
+    pub const fn rgba_linear(r: f32, g: f32, b: f32, a: f32) -> Color {
+        Color {
+            red: r,
+            green: g,
+            blue: b,
+            alpha: a,
+        }
     }
 
     pub fn hex<T: AsRef<str>>(hex: T) -> Result<Color, HexColorError> {
@@ -74,12 +111,14 @@ impl Color {
         Err(HexColorError::Length)
     }
 
+    /// New ``Color`` from sRGB colorspace.
     pub fn rgb_u8(r: u8, g: u8, b: u8) -> Color {
         Color::rgba_u8(r, g, b, u8::MAX)
     }
 
     // Float operations in const fn are not stable yet
     // see https://github.com/rust-lang/rust/issues/57241
+    /// New ``Color`` from sRGB colorspace.
     pub fn rgba_u8(r: u8, g: u8, b: u8, a: u8) -> Color {
         Color::rgba(
             r as f32 / u8::MAX as f32,
@@ -88,6 +127,82 @@ impl Color {
             a as f32 / u8::MAX as f32,
         )
     }
+
+    fn as_nonlinear_srgb_to_linear_srgb(self) -> Color {
+        Color {
+            red: self.red.nonlinear_to_linear_srgb(),
+            green: self.green.nonlinear_to_linear_srgb(),
+            blue: self.blue.nonlinear_to_linear_srgb(),
+            alpha: self.alpha, //alpha is always linear
+        }
+    }
+
+    // non-linear-sRGB Component Getter
+    pub fn r(&self) -> f32 {
+        self.red.linear_to_nonlinear_srgb()
+    }
+
+    pub fn g(&self) -> f32 {
+        self.red.linear_to_nonlinear_srgb()
+    }
+
+    pub fn b(&self) -> f32 {
+        self.red.linear_to_nonlinear_srgb()
+    }
+
+    // linear-sRGB Component Getter
+    pub fn g_linear(&self) -> f32 {
+        self.green
+    }
+
+    pub fn r_linear(&self) -> f32 {
+        self.red
+    }
+
+    pub fn b_linear(&self) -> f32 {
+        self.blue
+    }
+
+    pub fn a(&self) -> f32 {
+        self.alpha
+    }
+
+    // non-linear-sRGB Component Setter
+    pub fn set_r(&mut self, r: f32) -> &mut Self {
+        self.red = r.nonlinear_to_linear_srgb();
+        self
+    }
+
+    pub fn set_g(&mut self, g: f32) -> &mut Self {
+        self.green = g.nonlinear_to_linear_srgb();
+        self
+    }
+
+    pub fn set_b(&mut self, b: f32) -> &mut Self {
+        self.blue = b.nonlinear_to_linear_srgb();
+        self
+    }
+
+    // linear-sRGB Component Setter
+    pub fn set_r_linear(&mut self, r: f32) -> &mut Self {
+        self.red = r;
+        self
+    }
+
+    pub fn set_g_linear(&mut self, g: f32) -> &mut Self {
+        self.green = g;
+        self
+    }
+
+    pub fn set_b_linear(&mut self, b: f32) -> &mut Self {
+        self.blue = b;
+        self
+    }
+
+    pub fn set_a(&mut self, a: f32) -> &mut Self {
+        self.alpha = a;
+        self
+    }
 }
 
 impl Default for Color {
@@ -99,10 +214,10 @@ impl Default for Color {
 impl AddAssign<Color> for Color {
     fn add_assign(&mut self, rhs: Color) {
         *self = Color {
-            r: self.r + rhs.r,
+            red: self.red + rhs.red,
-            g: self.g + rhs.g,
+            green: self.green + rhs.green,
-            b: self.b + rhs.b,
+            blue: self.blue + rhs.blue,
-            a: self.a + rhs.a,
+            alpha: self.alpha + rhs.alpha,
         }
     }
 }
@@ -112,10 +227,10 @@ impl Add<Color> for Color {
 
     fn add(self, rhs: Color) -> Self::Output {
         Color {
-            r: self.r + rhs.r,
+            red: self.red + rhs.red,
-            g: self.g + rhs.g,
+            green: self.green + rhs.green,
-            b: self.b + rhs.b,
+            blue: self.blue + rhs.blue,
-            a: self.a + rhs.a,
+            alpha: self.alpha + rhs.alpha,
         }
     }
 }
@@ -125,10 +240,10 @@ impl Add<Vec4> for Color {
 
     fn add(self, rhs: Vec4) -> Self::Output {
         Color {
-            r: self.r + rhs.x(),
+            red: self.red + rhs.x(),
-            g: self.g + rhs.y(),
+            green: self.green + rhs.y(),
-            b: self.b + rhs.z(),
+            blue: self.blue + rhs.z(),
-            a: self.a + rhs.w(),
+            alpha: self.alpha + rhs.w(),
         }
     }
 }
@@ -136,17 +251,17 @@ impl Add<Vec4> for Color {
 impl From<Vec4> for Color {
     fn from(vec4: Vec4) -> Self {
         Color {
-            r: vec4.x(),
+            red: vec4.x(),
-            g: vec4.y(),
+            green: vec4.y(),
-            b: vec4.z(),
+            blue: vec4.z(),
-            a: vec4.w(),
+            alpha: vec4.w(),
         }
     }
 }
 
 impl Into<[f32; 4]> for Color {
     fn into(self) -> [f32; 4] {
-        [self.r, self.g, self.b, self.a]
+        [self.red, self.green, self.blue, self.alpha]
     }
 }
 impl Mul<f32> for Color {
@@ -154,20 +269,20 @@ impl Mul<f32> for Color {
 
     fn mul(self, rhs: f32) -> Self::Output {
         Color {
-            r: self.r * rhs,
+            red: self.red * rhs,
-            g: self.g * rhs,
+            green: self.green * rhs,
-            b: self.b * rhs,
+            blue: self.blue * rhs,
-            a: self.a * rhs,
+            alpha: self.alpha * rhs,
         }
     }
 }
 
 impl MulAssign<f32> for Color {
     fn mul_assign(&mut self, rhs: f32) {
-        self.r *= rhs;
+        self.red *= rhs;
-        self.g *= rhs;
+        self.green *= rhs;
-        self.b *= rhs;
+        self.blue *= rhs;
-        self.a *= rhs;
+        self.alpha *= rhs;
     }
 }
 
@@ -176,20 +291,20 @@ impl Mul<Vec4> for Color {
 
     fn mul(self, rhs: Vec4) -> Self::Output {
         Color {
-            r: self.r * rhs.x(),
+            red: self.red * rhs.x(),
-            g: self.g * rhs.y(),
+            green: self.green * rhs.y(),
-            b: self.b * rhs.z(),
+            blue: self.blue * rhs.z(),
-            a: self.a * rhs.w(),
+            alpha: self.alpha * rhs.w(),
         }
     }
 }
 
 impl MulAssign<Vec4> for Color {
     fn mul_assign(&mut self, rhs: Vec4) {
-        self.r *= rhs.x();
+        self.red *= rhs.x();
-        self.g *= rhs.y();
+        self.green *= rhs.y();
-        self.b *= rhs.z();
+        self.blue *= rhs.z();
-        self.a *= rhs.w();
+        self.alpha *= rhs.w();
     }
 }
 
@@ -198,19 +313,19 @@ impl Mul<Vec3> for Color {
 
     fn mul(self, rhs: Vec3) -> Self::Output {
         Color {
-            r: self.r * rhs.x(),
+            red: self.red * rhs.x(),
-            g: self.g * rhs.y(),
+            green: self.green * rhs.y(),
-            b: self.b * rhs.z(),
+            blue: self.blue * rhs.z(),
-            a: self.a,
+            alpha: self.alpha,
         }
     }
 }
 
 impl MulAssign<Vec3> for Color {
     fn mul_assign(&mut self, rhs: Vec3) {
-        self.r *= rhs.x();
+        self.red *= rhs.x();
-        self.g *= rhs.y();
+        self.green *= rhs.y();
-        self.b *= rhs.z();
+        self.blue *= rhs.z();
     }
 }
 
@@ -289,6 +404,17 @@ fn decode_rgba(data: &[u8]) -> Result<Color, HexColorError> {
     }
 }
 
+#[test]
+fn test_color_components_roundtrip() {
+    let mut color = Color::NONE;
+    color.set_r(0.5).set_g(0.5).set_b(0.5).set_a(0.5);
+    const EPS: f32 = 0.001;
+    assert!((color.r() - 0.5).abs() < EPS);
+    assert!((color.g() - 0.5).abs() < EPS);
+    assert!((color.b() - 0.5).abs() < EPS);
+    assert!((color.a() - 0.5).abs() < EPS);
+}
+
 #[test]
 fn test_hex_color() {
     assert_eq!(Color::hex("FFF").unwrap(), Color::rgb(1.0, 1.0, 1.0));

crates/bevy_render/src/colorspace.rs

@@ -0,0 +1,50 @@
+// sRGB
+//==================================================================================================
+pub trait SrgbColorSpace {
+    fn linear_to_nonlinear_srgb(self) -> Self;
+    fn nonlinear_to_linear_srgb(self) -> Self;
+}
+
+//source: https://entropymine.com/imageworsener/srgbformula/
+impl SrgbColorSpace for f32 {
+    fn linear_to_nonlinear_srgb(self) -> f32 {
+        if self <= 0.0 {
+            return self;
+        }
+
+        if self <= 0.0031308 {
+            self * 12.92 // linear falloff in dark values
+        } else {
+            (1.055 * self.powf(1.0 / 2.4)) - 0.055 //gamma curve in other area
+        }
+    }
+
+    fn nonlinear_to_linear_srgb(self) -> f32 {
+        if self <= 0.0 {
+            return self;
+        }
+        if self <= 0.04045 {
+            self / 12.92 // linear falloff in dark values
+        } else {
+            ((self + 0.055) / 1.055).powf(2.4) //gamma curve in other area
+        }
+    }
+}
+
+#[test]
+fn test_srgb_full_roundtrip() {
+    let u8max: f32 = u8::max_value() as f32;
+    for color in 0..u8::max_value() {
+        let color01 = color as f32 / u8max;
+        let color_roundtrip = color01
+            .linear_to_nonlinear_srgb()
+            .nonlinear_to_linear_srgb();
+        // roundtrip is not perfect due to numeric precision, even with f64
+        // so ensure the error is at least ready for u8 (where sRGB is used)
+        assert_eq!(
+            (color01 * u8max).round() as u8,
+            (color_roundtrip * u8max).round() as u8
+        );
+    }
+}
+//==================================================================================================

crates/bevy_render/src/lib.rs

@@ -1,6 +1,7 @@
 pub mod batch;
 pub mod camera;
 pub mod color;
+pub mod colorspace;
 pub mod draw;
 pub mod entity;
 pub mod mesh;

crates/bevy_text/src/font.rs

@@ -30,9 +30,9 @@ impl Font {
         // TODO: make this texture grayscale
         let color = Color::WHITE;
         let color_u8 = [
-            (color.r * 255.0) as u8,
+            (color.r() * 255.0) as u8,
-            (color.g * 255.0) as u8,
+            (color.g() * 255.0) as u8,
-            (color.b * 255.0) as u8,
+            (color.b() * 255.0) as u8,
         ];
         Texture::new(
             Vec2::new(width as f32, height as f32),
@@ -43,7 +43,7 @@ impl Font {
                         color_u8[0],
                         color_u8[1],
                         color_u8[2],
-                        (color.a * a * 255.0) as u8,
+                        (color.a() * a * 255.0) as u8,
                     ]
                 })
                 .flatten()
@@ -75,9 +75,9 @@ impl Font {
         );
 
         let color_u8 = [
-            (color.r * 255.0) as u8,
+            (color.r() * 255.0) as u8,
-            (color.g * 255.0) as u8,
+            (color.g() * 255.0) as u8,
-            (color.b * 255.0) as u8,
+            (color.b() * 255.0) as u8,
         ];
 
         // TODO: this offset is a bit hackey
@@ -108,7 +108,7 @@ impl Font {
                         color_u8[0],
                         color_u8[1],
                         color_u8[2],
-                        (color.a * a * 255.0) as u8,
+                        (color.a() * a * 255.0) as u8,
                     ]
                 })
                 .flatten()

crates/bevy_wgpu/src/wgpu_type_converter.rs

@@ -124,10 +124,10 @@ impl<'a> From<&'a OwnedWgpuVertexBufferDescriptor> for wgpu::VertexBufferDescrip
 impl WgpuFrom<Color> for wgpu::Color {
     fn from(color: Color) -> Self {
         wgpu::Color {
-            r: color.r as f64,
+            r: color.r_linear() as f64,
-            g: color.g as f64,
+            g: color.g_linear() as f64,
-            b: color.b as f64,
+            b: color.b_linear() as f64,
-            a: color.a as f64,
+            a: color.a() as f64,
         }
     }
 }