Serialize color names by packing them into DynamicColor

CHANGELOG.md

@@ -28,6 +28,7 @@ This release has an [MSRV][] of 1.82.
 * `AlphaColor`, `OpaqueColor`, and `PremulColor` now impl `PartialEq`. ([#76][], [#86][] by [@waywardmonkeys][])
 * `HueDirection` now impls `PartialEq`. ([#79][] by [@waywardmonkeys][])
 * `ColorSpaceTag` and `HueDirection` now have bytemuck support. ([#81][] by [@waywardmonkeys][])
+* A `DynamicColor` parsed from a named color or named color space function now serializes back to that name, as per the CSS Color Level 4 spec ([#39][] by [@tomcur][]).
 
 ### Changed
 
@@ -45,8 +46,10 @@ This is the initial release.
 
 [@MightyBurger]: https://github.com/MightyBurger
 [@raphlinus]: https://github.com/raphlinus
+[@tomcur]: https://github.com/tomcur
 [@waywardmonkeys]: https://github.com/waywardmonkeys
 
+[#39]: https://github.com/linebender/color/pull/39
 [#54]: https://github.com/linebender/color/pull/54
 [#61]: https://github.com/linebender/color/pull/61
 [#64]: https://github.com/linebender/color/pull/64

color/make_x11_colors.py

@@ -239,12 +239,16 @@ def minimal_perfect_hash(d):
 print("];")
 print()
 
-print(f"const NAMES: [&str; {n}] = [")
+print(f"pub(crate) const NAMES: [&str; {n}] = [")
 for (name, rgba) in keys:
     print(f'    "{name}",')
 print("];")
-print()
-print(f"const COLORS: [[u8; 4]; {n}] = [")
+print(f"""
+/// RGBA8 color components of the named X11 colors, in the same order as [`NAMES`].
+///
+/// Use [`lookup_palette_index`] to efficiently find the color components for a given color name
+/// string.
+pub(crate) const COLORS: [[u8; 4]; {n}] = [""")
 for (name, rgba) in keys:
     print(f'    {list(rgba)},')
 print("];")
@@ -260,15 +264,17 @@ def minimal_perfect_hash(d):
     (((y as u64) * (n as u64)) >> 32) as usize
 }
 
-pub(crate) fn lookup_palette(s: &str) -> Option<[u8; 4]> {
+/// Given a named color (e.g., "red", "mediumorchid"), returns the index of that color into
+/// [`COLORS`] and [`NAMES`].
+pub(crate) fn lookup_palette_index(s: &str) -> Option<usize> {
     let mut key = 0_u32;
     for b in s.as_bytes() {
         key = key.wrapping_mul(9).wrapping_add(*b as u32);
     }
     let salt = SALTS[weak_hash(key, 0, SALTS.len())] as u32;
     let ix = weak_hash(key, salt, SALTS.len());
     if s == NAMES[ix] {
-        Some(COLORS[ix])
+        Some(ix)
     } else {
         None
     }

color/src/dynamic.rs

@@ -5,7 +5,8 @@
 
 use crate::{
     color::{add_alpha, fixup_hues_for_interpolate, split_alpha},
-    AlphaColor, ColorSpace, ColorSpaceLayout, ColorSpaceTag, HueDirection, LinearSrgb, Missing,
+    AlphaColor, ColorSpace, ColorSpaceLayout, ColorSpaceTag, Flags, HueDirection, LinearSrgb,
+    Missing,
 };
 use core::hash::{Hash, Hasher};
 
@@ -31,8 +32,9 @@ use core::hash::{Hash, Hasher};
 pub struct DynamicColor {
     /// The color space.
     pub cs: ColorSpaceTag,
-    /// A bitmask of missing components.
-    pub missing: Missing,
+    /// The state of this color, tracking whether it has missing components and how it was
+    /// constructed. See the documentation of [`Flags`] for more information.
+    pub flags: Flags,
     /// The components.
     ///
     /// The first three components are interpreted according to the
@@ -77,7 +79,7 @@ impl DynamicColor {
         if let Some(cs) = CS::TAG {
             Self {
                 cs,
-                missing: Missing::default(),
+                flags: Flags::default(),
                 components: color.components,
             }
         } else {
@@ -97,23 +99,23 @@ impl DynamicColor {
             let (opaque, alpha) = split_alpha(self.components);
             let mut components = add_alpha(self.cs.convert(cs, opaque), alpha);
             // Reference: §12.2 of Color 4 spec
-            let missing = if !self.missing.is_empty() {
+            let missing = if !self.flags.missing().is_empty() {
                 if self.cs.same_analogous(cs) {
                     for (i, component) in components.iter_mut().enumerate() {
-                        if self.missing.contains(i) {
+                        if self.flags.missing().contains(i) {
                             *component = 0.0;
                         }
                     }
-                    self.missing
+                    self.flags.missing()
                 } else {
-                    let mut missing = self.missing & Missing::single(3);
-                    if self.cs.h_missing(self.missing) {
+                    let mut missing = self.flags.missing() & Missing::single(3);
+                    if self.cs.h_missing(self.flags.missing()) {
                         cs.set_h_missing(&mut missing, &mut components);
                     }
-                    if self.cs.c_missing(self.missing) {
+                    if self.cs.c_missing(self.flags.missing()) {
                         cs.set_c_missing(&mut missing, &mut components);
                     }
-                    if self.cs.l_missing(self.missing) {
+                    if self.cs.l_missing(self.flags.missing()) {
                         cs.set_l_missing(&mut missing, &mut components);
                     }
                     missing
@@ -123,7 +125,7 @@ impl DynamicColor {
             };
             let mut result = Self {
                 cs,
-                missing,
+                flags: Flags::from_missing(missing),
                 components,
             };
             result.powerless_to_missing();
@@ -137,9 +139,9 @@ impl DynamicColor {
     /// a corresponding component which is 0. This method restores that
     /// invariant after manipulation which might invalidate it.
     fn zero_missing_components(mut self) -> Self {
-        if !self.missing.is_empty() {
+        if !self.flags.missing().is_empty() {
             for (i, component) in self.components.iter_mut().enumerate() {
-                if self.missing.contains(i) {
+                if self.flags.missing().contains(i) {
                     *component = 0.0;
                 }
             }
@@ -153,13 +155,13 @@ impl DynamicColor {
     /// will be ignored and the color returned unchanged.
     #[must_use]
     pub const fn multiply_alpha(self, rhs: f32) -> Self {
-        if self.missing.contains(3) {
+        if self.flags.missing().contains(3) {
             self
         } else {
             let (opaque, alpha) = split_alpha(self.components);
             Self {
                 cs: self.cs,
-                missing: self.missing,
+                flags: Flags::from_missing(self.flags.missing()),
                 components: add_alpha(opaque, alpha * rhs),
             }
         }
@@ -181,13 +183,13 @@ impl DynamicColor {
     /// ```
     #[must_use]
     pub const fn with_alpha(self, alpha: f32) -> Self {
-        if self.missing.contains(3) {
+        if self.flags.missing().contains(3) {
             self
         } else {
             let (opaque, _alpha) = split_alpha(self.components);
             Self {
                 cs: self.cs,
-                missing: self.missing,
+                flags: Flags::from_missing(self.flags.missing()),
                 components: add_alpha(opaque, alpha),
             }
         }
@@ -200,9 +202,12 @@ impl DynamicColor {
     pub fn scale_chroma(self, scale: f32) -> Self {
         let (opaque, alpha) = split_alpha(self.components);
         let components = self.cs.scale_chroma(opaque, scale);
+
+        let mut flags = self.flags;
+        flags.discard_name();
         Self {
             cs: self.cs,
-            missing: self.missing,
+            flags,
             components: add_alpha(components, alpha),
         }
         .zero_missing_components()
@@ -219,15 +224,15 @@ impl DynamicColor {
         let alpha = alpha.clamp(0., 1.);
         Self {
             cs: self.cs,
-            missing: self.missing,
+            flags: self.flags,
             components: add_alpha(components, alpha),
         }
     }
 
     fn premultiply_split(self) -> ([f32; 3], f32) {
         // Reference: §12.3 of Color 4 spec
         let (opaque, alpha) = split_alpha(self.components);
-        let premul = if alpha == 1.0 || self.missing.contains(3) {
+        let premul = if alpha == 1.0 || self.flags.missing().contains(3) {
             opaque
         } else {
             self.cs.layout().scale(opaque, alpha)
@@ -243,8 +248,9 @@ impl DynamicColor {
         if self.cs.layout() != ColorSpaceLayout::Rectangular
             && self.components[1] < POWERLESS_EPSILON
         {
-            self.cs
-                .set_h_missing(&mut self.missing, &mut self.components);
+            let mut missing = self.flags.missing();
+            self.cs.set_h_missing(&mut missing, &mut self.components);
+            self.flags.set_missing(missing);
         }
     }
 
@@ -262,12 +268,14 @@ impl DynamicColor {
     ) -> Interpolator {
         let mut a = self.convert(cs);
         let mut b = other.convert(cs);
-        let missing = a.missing & b.missing;
-        if self.missing != other.missing {
+        let a_missing = a.flags.missing();
+        let b_missing = b.flags.missing();
+        let missing = a_missing & b_missing;
+        if a_missing != b_missing {
             for i in 0..4 {
-                if (a.missing & !b.missing).contains(i) {
+                if (a_missing & !b_missing).contains(i) {
                     a.components[i] = b.components[i];
-                } else if (!a.missing & b.missing).contains(i) {
+                } else if (!a_missing & b_missing).contains(i) {
                     b.components[i] = a.components[i];
                 }
             }
@@ -310,9 +318,12 @@ impl DynamicColor {
     #[must_use]
     pub fn map(self, f: impl Fn(f32, f32, f32, f32) -> [f32; 4]) -> Self {
         let [x, y, z, a] = self.components;
+
+        let mut flags = self.flags;
+        flags.discard_name();
         Self {
             cs: self.cs,
-            missing: self.missing,
+            flags,
             components: f(x, y, z, a),
         }
         .zero_missing_components()
@@ -371,7 +382,7 @@ impl Hash for DynamicColor {
     /// match behavior for Rust float types.
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.cs.hash(state);
-        self.missing.hash(state);
+        self.flags.hash(state);
         for c in self.components {
             c.to_bits().hash(state);
         }
@@ -382,7 +393,7 @@ impl PartialEq for DynamicColor {
     /// Equality is determined based on the bit representation.
     fn eq(&self, other: &Self) -> bool {
         self.cs == other.cs
-            && self.missing == other.missing
+            && self.flags == other.flags
             && self.components[0].to_bits() == other.components[0].to_bits()
             && self.components[1].to_bits() == other.components[1].to_bits()
             && self.components[2].to_bits() == other.components[2].to_bits()
@@ -410,29 +421,34 @@ impl Interpolator {
         let components = add_alpha(opaque, alpha);
         DynamicColor {
             cs: self.cs,
-            missing: self.missing,
+            flags: Flags::from_missing(self.missing),
             components,
         }
     }
 }
 
 #[cfg(test)]
 mod tests {
-    use crate::{parse_color, Missing};
+    use crate::{parse_color, DynamicColor, Missing};
+
+    // `DynamicColor` was carefully packed. Ensure its size doesn't accidentally change.
+    const _: () = if size_of::<DynamicColor>() != 20 {
+        panic!("`DynamicColor` size changed");
+    };
 
     #[test]
     fn missing_alpha() {
         let c = parse_color("oklab(0.5 0.2 0 / none)").unwrap();
         assert_eq!(0., c.components[3]);
-        assert_eq!(Missing::single(3), c.missing);
+        assert_eq!(Missing::single(3), c.flags.missing());
 
         // Alpha is missing, so we shouldn't be able to get an alpha added.
         let c2 = c.with_alpha(0.5);
         assert_eq!(0., c2.components[3]);
-        assert_eq!(Missing::single(3), c2.missing);
+        assert_eq!(Missing::single(3), c2.flags.missing());
 
         let c3 = c.multiply_alpha(0.2);
         assert_eq!(0., c3.components[3]);
-        assert_eq!(Missing::single(3), c3.missing);
+        assert_eq!(Missing::single(3), c3.flags.missing());
     }
 }