Introduce web-colors feature flag to enable sRGB linear blending

This is how browsers perform color management. They treat
gamma-corrected sRGB colors as if they were linear RGB.

Correctness aside, this mode is introduced for legacy reasons. Most
UI/UX tooling uses this color management as well, and many have created
an intuition about how color should behave from interacting with a
browser.

This feature flag should facilitate application development with `iced`
in those cases.

More details: https://webcolorisstillbroken.com/

graphics/Cargo.toml

@@ -14,6 +14,7 @@ categories = ["gui"]
 geometry = ["lyon_path"]
 opengl = []
 image = ["dep:image", "kamadak-exif"]
+web-colors = []
 
 [dependencies]
 glam = "0.24"

graphics/src/color.rs

@@ -0,0 +1,46 @@
+//! Manage colors for shaders.
+use crate::core::Color;
+
+use bytemuck::{Pod, Zeroable};
+
+/// A color packed as 4 floats representing RGBA channels.
+#[derive(Debug, Clone, Copy, PartialEq, Zeroable, Pod)]
+#[repr(C)]
+pub struct Packed([f32; 4]);
+
+impl Packed {
+    /// Returns the internal components of the [`Packed`] color.
+    pub fn components(self) -> [f32; 4] {
+        self.0
+    }
+}
+
+/// A flag that indicates whether the renderer should perform gamma correction.
+pub const GAMMA_CORRECTION: bool = internal::GAMMA_CORRECTION;
+
+/// Packs a [`Color`].
+pub fn pack(color: impl Into<Color>) -> Packed {
+    Packed(internal::pack(color.into()))
+}
+
+#[cfg(not(feature = "web-colors"))]
+mod internal {
+    use crate::core::Color;
+
+    pub const GAMMA_CORRECTION: bool = true;
+
+    pub fn pack(color: Color) -> [f32; 4] {
+        color.into_linear()
+    }
+}
+
+#[cfg(feature = "web-colors")]
+mod internal {
+    use crate::core::Color;
+
+    pub const GAMMA_CORRECTION: bool = false;
+
+    pub fn pack(color: Color) -> [f32; 4] {
+        [color.r, color.g, color.b, color.a]
+    }
+}

graphics/src/gradient.rs

@@ -3,8 +3,10 @@
 //! For a gradient that you can use as a background variant for a widget, see [`Gradient`].
 //!
 //! [`Gradient`]: crate::core::Gradient;
+use crate::color;
 use crate::core::gradient::ColorStop;
 use crate::core::{self, Color, Point, Rectangle};
+
 use std::cmp::Ordering;
 
 #[derive(Debug, Clone, PartialEq)]
@@ -101,7 +103,8 @@ impl Linear {
 
         for (index, stop) in self.stops.iter().enumerate() {
             let [r, g, b, a] =
-                stop.map_or(Color::default(), |s| s.color).into_linear();
+                color::pack(stop.map_or(Color::default(), |s| s.color))
+                    .components();
 
             data[index * 4] = r;
             data[(index * 4) + 1] = g;
@@ -133,7 +136,8 @@ pub fn pack(gradient: &core::Gradient, bounds: Rectangle) -> Packed {
 
             for (index, stop) in linear.stops.iter().enumerate() {
                 let [r, g, b, a] =
-                    stop.map_or(Color::default(), |s| s.color).into_linear();
+                    color::pack(stop.map_or(Color::default(), |s| s.color))
+                        .components();
 
                 data[index * 4] = r;
                 data[(index * 4) + 1] = g;

graphics/src/lib.rs

@@ -27,6 +27,7 @@ mod transformation;
 mod viewport;
 
 pub mod backend;
+pub mod color;
 pub mod compositor;
 pub mod damage;
 pub mod gradient;

graphics/src/primitive.rs

@@ -1,4 +1,5 @@
 //! Draw using different graphical primitives.
+use crate::color;
 use crate::core::alignment;
 use crate::core::image;
 use crate::core::svg;
@@ -248,7 +249,7 @@ pub struct ColoredVertex2D {
     pub position: [f32; 2],
 
     /// The color of the vertex in __linear__ RGBA.
-    pub color: [f32; 4],
+    pub color: color::Packed,
 }
 
 /// A vertex which contains 2D position & packed gradient data.