style: Extend StyleComplexColor to support additive blending.

Refactored StyleComplexColor to support "complex" blending between
background (numeric) color and foreground color (currentColor).
Made explicit the distinction between numeric, currentColor and a
complex blend in Gecko and Stylo.

This is to support SMIL animation, for example, of the form:

     <animate from="rgb(10,20,30)" by="currentColor" ... />

Bug: 1465307
Reviewed-by: hiro,xidorn
MozReview-Commit-ID: IUAK8P07gtm

components/style/gecko_bindings/sugar/style_complex_color.rs

@@ -5,28 +5,21 @@
 //! Rust helpers to interact with Gecko's StyleComplexColor.
 
 use gecko::values::{convert_nscolor_to_rgba, convert_rgba_to_nscolor};
-use gecko_bindings::structs::{nscolor, StyleComplexColor};
+use gecko_bindings::structs::StyleComplexColor;
+use gecko_bindings::structs::StyleComplexColor_Tag as Tag;
 use values::{Auto, Either};
-use values::computed::Color as ComputedColor;
+use values::computed::{Color as ComputedColor, RGBAColor as ComputedRGBA};
+use values::computed::ComplexColorRatios;
 use values::computed::ui::ColorOrAuto;
 
-impl From<nscolor> for StyleComplexColor {
-    fn from(other: nscolor) -> Self {
-        StyleComplexColor {
-            mColor: other,
-            mForegroundRatio: 0,
-            mIsAuto: false,
-        }
-    }
-}
-
 impl StyleComplexColor {
     /// Create a `StyleComplexColor` value that represents `currentColor`.
     pub fn current_color() -> Self {
         StyleComplexColor {
             mColor: 0,
-            mForegroundRatio: 255,
-            mIsAuto: false,
+            mBgRatio: 0.,
+            mFgRatio: 1.,
+            mTag: Tag::eForeground,
         }
     }
 
@@ -34,28 +27,66 @@ impl StyleComplexColor {
     pub fn auto() -> Self {
         StyleComplexColor {
             mColor: 0,
-            mForegroundRatio: 255,
-            mIsAuto: true,
+            mBgRatio: 0.,
+            mFgRatio: 1.,
+            mTag: Tag::eAuto,
+        }
+    }
+}
+
+impl From<ComputedRGBA> for StyleComplexColor {
+    fn from(other: ComputedRGBA) -> Self {
+        StyleComplexColor {
+            mColor: convert_rgba_to_nscolor(&other),
+            mBgRatio: 1.,
+            mFgRatio: 0.,
+            mTag: Tag::eNumeric,
         }
     }
 }
 
 impl From<ComputedColor> for StyleComplexColor {
     fn from(other: ComputedColor) -> Self {
-        StyleComplexColor {
-            mColor: convert_rgba_to_nscolor(&other.color).into(),
-            mForegroundRatio: other.foreground_ratio,
-            mIsAuto: false,
+        match other {
+            ComputedColor::Numeric(color) => color.into(),
+            ComputedColor::Foreground => Self::current_color(),
+            ComputedColor::Complex(color, ratios) => {
+                debug_assert!(ratios != ComplexColorRatios::NUMERIC);
+                debug_assert!(ratios != ComplexColorRatios::FOREGROUND);
+                StyleComplexColor {
+                    mColor: convert_rgba_to_nscolor(&color).into(),
+                    mBgRatio: ratios.bg,
+                    mFgRatio: ratios.fg,
+                    mTag: Tag::eComplex,
+                }
+            }
         }
     }
 }
 
 impl From<StyleComplexColor> for ComputedColor {
     fn from(other: StyleComplexColor) -> Self {
-        debug_assert!(!other.mIsAuto);
-        ComputedColor {
-            color: convert_nscolor_to_rgba(other.mColor),
-            foreground_ratio: other.mForegroundRatio,
+        match other.mTag {
+            Tag::eNumeric => {
+                debug_assert!(other.mBgRatio == 1. && other.mFgRatio == 0.);
+                ComputedColor::Numeric(convert_nscolor_to_rgba(other.mColor))
+            }
+            Tag::eForeground => {
+                debug_assert!(other.mBgRatio == 0. && other.mFgRatio == 1.);
+                ComputedColor::Foreground
+            }
+            Tag::eComplex => {
+                debug_assert!(other.mBgRatio != 1. || other.mFgRatio != 0.);
+                debug_assert!(other.mBgRatio != 0. || other.mFgRatio != 1.);
+                ComputedColor::Complex(
+                    convert_nscolor_to_rgba(other.mColor),
+                    ComplexColorRatios {
+                        bg: other.mBgRatio,
+                        fg: other.mFgRatio,
+                    },
+                )
+            }
+            Tag::eAuto => unreachable!("Unsupport StyleComplexColor with tag eAuto"),
         }
     }
 }
@@ -71,7 +102,7 @@ impl From<ColorOrAuto> for StyleComplexColor {
 
 impl From<StyleComplexColor> for ColorOrAuto {
     fn from(other: StyleComplexColor) -> Self {
-        if !other.mIsAuto {
+        if other.mTag != Tag::eAuto {
             Either::First(other.into())
         } else {
             Either::Second(Auto)

components/style/values/animated/color.rs

@@ -6,6 +6,7 @@
 
 use values::animated::{Animate, Procedure, ToAnimatedZero};
 use values::distance::{ComputeSquaredDistance, SquaredDistance};
+use values::computed::ComplexColorRatios;
 
 /// An animated RGBA color.
 ///
@@ -91,42 +92,51 @@ impl ComputeSquaredDistance for RGBA {
     }
 }
 
+impl Animate for ComplexColorRatios {
+    #[inline]
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        let bg = self.bg.animate(&other.bg, procedure)?;
+        let fg = self.fg.animate(&other.fg, procedure)?;
+
+        Ok(ComplexColorRatios { bg, fg })
+    }
+}
+
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 #[derive(Clone, Copy, Debug, PartialEq)]
-pub struct Color {
-    pub color: RGBA,
-    pub foreground_ratio: f32,
+pub enum Color {
+    Numeric(RGBA),
+    Foreground,
+    Complex(RGBA, ComplexColorRatios),
 }
 
 impl Color {
     fn currentcolor() -> Self {
-        Color {
-            color: RGBA::transparent(),
-            foreground_ratio: 1.,
-        }
+        Color::Foreground
     }
 
     /// Returns a transparent intermediate color.
     pub fn transparent() -> Self {
-        Color {
-            color: RGBA::transparent(),
-            foreground_ratio: 0.,
-        }
-    }
-
-    fn is_currentcolor(&self) -> bool {
-        self.foreground_ratio >= 1.
-    }
-
-    fn is_numeric(&self) -> bool {
-        self.foreground_ratio <= 0.
+        Color::Numeric(RGBA::transparent())
     }
 
     fn effective_intermediate_rgba(&self) -> RGBA {
-        RGBA {
-            alpha: self.color.alpha * (1. - self.foreground_ratio),
-            ..self.color
+        match *self {
+            Color::Numeric(color) => color,
+            Color::Foreground => RGBA::transparent(),
+            Color::Complex(color, ratios) => RGBA {
+                alpha: color.alpha * ratios.bg,
+                ..color.clone()
+            },
+        }
+    }
+
+    fn effective_ratios(&self) -> ComplexColorRatios {
+        match *self {
+            Color::Numeric(..) => ComplexColorRatios::NUMERIC,
+            Color::Foreground => ComplexColorRatios::FOREGROUND,
+            Color::Complex(.., ratios) => ratios,
         }
     }
 }
@@ -136,50 +146,66 @@ impl Animate for Color {
     fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
         // Common cases are interpolating between two numeric colors,
         // two currentcolors, and a numeric color and a currentcolor.
-        //
-        // Note: this algorithm assumes self_portion + other_portion
-        // equals to one, so it may be broken for additive operation.
-        // To properly support additive color interpolation, we would
-        // need two ratio fields in computed color types.
         let (this_weight, other_weight) = procedure.weights();
-        if self.foreground_ratio == other.foreground_ratio {
-            if self.is_currentcolor() {
-                Ok(Color::currentcolor())
-            } else {
-                Ok(Color {
-                    color: self.color.animate(&other.color, procedure)?,
-                    foreground_ratio: self.foreground_ratio,
-                })
+
+        Ok(match (*self, *other, procedure) {
+            // Any interpolation of currentColor with currentColor returns currentColor.
+            (Color::Foreground, Color::Foreground, Procedure::Interpolate { .. }) => {
+                Color::currentcolor()
             }
-        } else if self.is_currentcolor() && other.is_numeric() {
-            Ok(Color {
-                color: other.color,
-                foreground_ratio: this_weight as f32,
-            })
-        } else if self.is_numeric() && other.is_currentcolor() {
-            Ok(Color {
-                color: self.color,
-                foreground_ratio: other_weight as f32,
-            })
-        } else {
-            // For interpolating between two complex colors, we need to
-            // generate colors with effective alpha value.
-            let self_color = self.effective_intermediate_rgba();
-            let other_color = other.effective_intermediate_rgba();
-            let color = self_color.animate(&other_color, procedure)?;
-            // Then we compute the final foreground ratio, and derive
-            // the final alpha value from the effective alpha value.
-            let foreground_ratio = self.foreground_ratio
-                .animate(&other.foreground_ratio, procedure)?;
-            let alpha = color.alpha / (1. - foreground_ratio);
-            Ok(Color {
-                color: RGBA {
-                    alpha: alpha,
-                    ..color
+            // Animating two numeric colors.
+            (Color::Numeric(c1), Color::Numeric(c2), _) => {
+                Color::Numeric(c1.animate(&c2, procedure)?)
+            }
+            // Combinations of numeric color and currentColor
+            (Color::Foreground, Color::Numeric(color), _) => Color::Complex(
+                color,
+                ComplexColorRatios {
+                    bg: other_weight as f32,
+                    fg: this_weight as f32,
                 },
-                foreground_ratio: foreground_ratio,
-            })
-        }
+            ),
+            (Color::Numeric(color), Color::Foreground, _) => Color::Complex(
+                color,
+                ComplexColorRatios {
+                    bg: this_weight as f32,
+                    fg: other_weight as f32,
+                },
+            ),
+
+            // Any other animation of currentColor with currentColor is complex.
+            (Color::Foreground, Color::Foreground, _) => Color::Complex(
+                RGBA::transparent(),
+                ComplexColorRatios {
+                    bg: 0.,
+                    fg: (this_weight + other_weight) as f32,
+                },
+            ),
+
+            // Defer to complex calculations
+            _ => {
+                // For interpolating between two complex colors, we need to
+                // generate colors with effective alpha value.
+                let self_color = self.effective_intermediate_rgba();
+                let other_color = other.effective_intermediate_rgba();
+                let color = self_color.animate(&other_color, procedure)?;
+                // Then we compute the final background ratio, and derive
+                // the final alpha value from the effective alpha value.
+                let self_ratios = self.effective_ratios();
+                let other_ratios = other.effective_ratios();
+                let ratios = self_ratios.animate(&other_ratios, procedure)?;
+                let alpha = color.alpha / ratios.bg;
+                let color = RGBA { alpha, ..color };
+
+                if ratios == ComplexColorRatios::NUMERIC {
+                    Color::Numeric(color)
+                } else if ratios == ComplexColorRatios::FOREGROUND {
+                    Color::Foreground
+                } else {
+                    Color::Complex(color, ratios)
+                }
+            }
+        })
     }
 }
 
@@ -187,27 +213,26 @@ impl ComputeSquaredDistance for Color {
     #[inline]
     fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
         // All comments from the Animate impl also applies here.
-        if self.foreground_ratio == other.foreground_ratio {
-            if self.is_currentcolor() {
-                Ok(SquaredDistance::from_sqrt(0.))
-            } else {
-                self.color.compute_squared_distance(&other.color)
+        Ok(match (*self, *other) {
+            (Color::Foreground, Color::Foreground) => SquaredDistance::from_sqrt(0.),
+            (Color::Numeric(c1), Color::Numeric(c2)) => c1.compute_squared_distance(&c2)?,
+            (Color::Foreground, Color::Numeric(color))
+            | (Color::Numeric(color), Color::Foreground) => {
+                // `computed_squared_distance` is symmetic.
+                color.compute_squared_distance(&RGBA::transparent())?
+                    + SquaredDistance::from_sqrt(1.)
             }
-        } else if self.is_currentcolor() && other.is_numeric() {
-            Ok(
-                RGBA::transparent().compute_squared_distance(&other.color)? +
-                    SquaredDistance::from_sqrt(1.),
-            )
-        } else if self.is_numeric() && other.is_currentcolor() {
-            Ok(self.color.compute_squared_distance(&RGBA::transparent())? +
-                SquaredDistance::from_sqrt(1.))
-        } else {
-            let self_color = self.effective_intermediate_rgba();
-            let other_color = other.effective_intermediate_rgba();
-            Ok(self_color.compute_squared_distance(&other_color)? +
-                self.foreground_ratio
-                    .compute_squared_distance(&other.foreground_ratio)?)
-        }
+            (_, _) => {
+                let self_color = self.effective_intermediate_rgba();
+                let other_color = other.effective_intermediate_rgba();
+                let self_ratios = self.effective_ratios();
+                let other_ratios = other.effective_ratios();
+
+                self_color.compute_squared_distance(&other_color)?
+                    + self_ratios.bg.compute_squared_distance(&other_ratios.bg)?
+                    + self_ratios.fg.compute_squared_distance(&other_ratios.fg)?
+            }
+        })
     }
 }
 

components/style/values/computed/color.rs

@@ -10,17 +10,36 @@ use style_traits::{CssWriter, ToCss};
 use values::animated::ToAnimatedValue;
 use values::animated::color::{Color as AnimatedColor, RGBA as AnimatedRGBA};
 
-/// This struct represents a combined color from a numeric color and
-/// the current foreground color (currentcolor keyword).
-/// Conceptually, the formula is "color * (1 - p) + currentcolor * p"
-/// where p is foreground_ratio.
-#[derive(Clone, Copy, Debug, MallocSizeOf)]
-pub struct Color {
-    /// RGBA color.
-    pub color: RGBA,
+/// Ratios representing the contribution of color and currentcolor to
+/// the final color value.
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq)]
+pub struct ComplexColorRatios {
+    /// Numeric color contribution.
+    pub bg: f32,
+    /// Foreground color, aka currentcolor, contribution.
+    pub fg: f32,
+}
 
-    /// The ratio of currentcolor in complex color.
-    pub foreground_ratio: u8,
+impl ComplexColorRatios {
+    /// Ratios representing pure numeric color.
+    pub const NUMERIC: ComplexColorRatios = ComplexColorRatios { bg: 1., fg: 0. };
+    /// Ratios representing pure foreground color.
+    pub const FOREGROUND: ComplexColorRatios = ComplexColorRatios { bg: 0., fg: 1. };
+}
+
+/// This enum represents a combined color from a numeric color and
+/// the current foreground color (currentColor keyword).
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq)]
+pub enum Color {
+    ///  Numeric RGBA color.
+    Numeric(RGBA),
+
+    /// The current foreground color.
+    Foreground,
+
+    /// A linear combination of numeric color and currentColor.
+    /// The formula is: `color * bg_ratio + currentColor * fg_ratio`.
+    Complex(RGBA, ComplexColorRatios),
 }
 
 /// Computed value type for the specified RGBAColor.
@@ -31,11 +50,8 @@ pub type ColorPropertyValue = RGBA;
 
 impl Color {
     /// Returns a numeric color representing the given RGBA value.
-    pub fn rgba(rgba: RGBA) -> Color {
-        Color {
-            color: rgba,
-            foreground_ratio: 0,
-        }
+    pub fn rgba(color: RGBA) -> Color {
+        Color::Numeric(color)
     }
 
     /// Returns a complex color value representing transparent.
@@ -45,73 +61,53 @@ impl Color {
 
     /// Returns a complex color value representing currentcolor.
     pub fn currentcolor() -> Color {
-        Color {
-            color: RGBA::transparent(),
-            foreground_ratio: u8::max_value(),
-        }
+        Color::Foreground
     }
 
     /// Whether it is a numeric color (no currentcolor component).
     pub fn is_numeric(&self) -> bool {
-        self.foreground_ratio == 0
+        matches!(*self, Color::Numeric { .. })
     }
 
     /// Whether it is a currentcolor value (no numeric color component).
     pub fn is_currentcolor(&self) -> bool {
-        self.foreground_ratio == u8::max_value()
+        matches!(*self, Color::Foreground)
     }
 
     /// Combine this complex color with the given foreground color into
     /// a numeric RGBA color. It currently uses linear blending.
     pub fn to_rgba(&self, fg_color: RGBA) -> RGBA {
-        // Common cases that the complex color is either pure numeric
-        // color or pure currentcolor.
-        if self.is_numeric() {
-            return self.color;
-        }
-        if self.is_currentcolor() {
-            return fg_color.clone();
-        }
-
-        fn blend_color_component(bg: u8, fg: u8, fg_alpha: u8) -> u8 {
-            let bg_ratio = (u8::max_value() - fg_alpha) as u32;
-            let fg_ratio = fg_alpha as u32;
-            let color = bg as u32 * bg_ratio + fg as u32 * fg_ratio;
-            // Rounding divide the number by 255
-            ((color + 127) / 255) as u8
-        }
-
-        // Common case that alpha channel is equal (usually both are opaque).
-        let fg_ratio = self.foreground_ratio;
-        if self.color.alpha == fg_color.alpha {
-            let r = blend_color_component(self.color.red, fg_color.red, fg_ratio);
-            let g = blend_color_component(self.color.green, fg_color.green, fg_ratio);
-            let b = blend_color_component(self.color.blue, fg_color.blue, fg_ratio);
-            return RGBA::new(r, g, b, fg_color.alpha);
-        }
+        let (color, ratios) = match *self {
+            // Common cases that the complex color is either pure numeric
+            // color or pure currentcolor.
+            Color::Numeric(color) => return color,
+            Color::Foreground => return fg_color,
+            Color::Complex(color, ratios) => (color, ratios),
+        };
 
         // For the more complicated case that the alpha value differs,
         // we use the following formula to compute the components:
-        // alpha = self_alpha * (1 - fg_ratio) + fg_alpha * fg_ratio
-        // color = (self_color * self_alpha * (1 - fg_ratio) +
+        // alpha = self_alpha * bg_ratio + fg_alpha * fg_ratio
+        // color = (self_color * self_alpha * bg_ratio +
         //          fg_color * fg_alpha * fg_ratio) / alpha
 
-        let p1 = (1. / 255.) * (255 - fg_ratio) as f32;
-        let a1 = self.color.alpha_f32();
-        let r1 = a1 * self.color.red_f32();
-        let g1 = a1 * self.color.green_f32();
-        let b1 = a1 * self.color.blue_f32();
+        let p1 = ratios.bg;
+        let a1 = color.alpha_f32();
+        let r1 = a1 * color.red_f32();
+        let g1 = a1 * color.green_f32();
+        let b1 = a1 * color.blue_f32();
 
-        let p2 = 1. - p1;
+        let p2 = ratios.fg;
         let a2 = fg_color.alpha_f32();
         let r2 = a2 * fg_color.red_f32();
         let g2 = a2 * fg_color.green_f32();
         let b2 = a2 * fg_color.blue_f32();
 
         let a = p1 * a1 + p2 * a2;
-        if a == 0.0 {
+        if a <= 0. {
             return RGBA::transparent();
         }
+        let a = f32::min(a, 1.);
 
         let inverse_a = 1. / a;
         let r = (p1 * r1 + p2 * r2) * inverse_a;
@@ -121,19 +117,9 @@ impl Color {
     }
 }
 
-impl PartialEq for Color {
-    fn eq(&self, other: &Color) -> bool {
-        self.foreground_ratio == other.foreground_ratio &&
-            (self.is_currentcolor() || self.color == other.color)
-    }
-}
-
 impl From<RGBA> for Color {
     fn from(color: RGBA) -> Color {
-        Color {
-            color: color,
-            foreground_ratio: 0,
-        }
+        Color::Numeric(color)
     }
 }
 
@@ -142,12 +128,10 @@ impl ToCss for Color {
     where
         W: fmt::Write,
     {
-        if self.is_numeric() {
-            self.color.to_css(dest)
-        } else if self.is_currentcolor() {
-            CSSParserColor::CurrentColor.to_css(dest)
-        } else {
-            Ok(())
+        match *self {
+            Color::Numeric(color) => color.to_css(dest),
+            Color::Foreground => CSSParserColor::CurrentColor.to_css(dest),
+            _ => Ok(()),
         }
     }
 }
@@ -157,17 +141,23 @@ impl ToAnimatedValue for Color {
 
     #[inline]
     fn to_animated_value(self) -> Self::AnimatedValue {
-        AnimatedColor {
-            color: self.color.to_animated_value(),
-            foreground_ratio: self.foreground_ratio as f32 * (1. / 255.),
+        match self {
+            Color::Numeric(color) => AnimatedColor::Numeric(color.to_animated_value()),
+            Color::Foreground => AnimatedColor::Foreground,
+            Color::Complex(color, ratios) => {
+                AnimatedColor::Complex(color.to_animated_value(), ratios)
+            }
         }
     }
 
     #[inline]
     fn from_animated_value(animated: Self::AnimatedValue) -> Self {
-        Color {
-            color: RGBA::from_animated_value(animated.color),
-            foreground_ratio: (animated.foreground_ratio * 255.).round() as u8,
+        match animated {
+            AnimatedColor::Numeric(color) => Color::Numeric(RGBA::from_animated_value(color)),
+            AnimatedColor::Foreground => Color::Foreground,
+            AnimatedColor::Complex(color, ratios) => {
+                Color::Complex(RGBA::from_animated_value(color), ratios)
+            }
         }
     }
 }

components/style/values/computed/mod.rs

@@ -45,7 +45,7 @@ pub use self::font::{MozScriptLevel, MozScriptMinSize, MozScriptSizeMultiplier,
 pub use self::box_::{AnimationIterationCount, AnimationName, Contain, Display, TransitionProperty};
 pub use self::box_::{OverflowClipBox, OverscrollBehavior, Perspective};
 pub use self::box_::{ScrollSnapType, TouchAction, VerticalAlign, WillChange};
-pub use self::color::{Color, ColorPropertyValue, RGBAColor};
+pub use self::color::{Color, ColorPropertyValue, ComplexColorRatios, RGBAColor};
 pub use self::column::ColumnCount;
 pub use self::counters::{Content, ContentItem, CounterIncrement, CounterReset};
 pub use self::effects::{BoxShadow, Filter, SimpleShadow};

components/style/values/specified/color.rs

@@ -88,11 +88,11 @@ impl<'a, 'b: 'a, 'i: 'a> ::cssparser::ColorComponentParser<'i> for ColorComponen
                 };
 
                 Ok(AngleOrNumber::Angle { degrees })
-            },
+            }
             Token::Number { value, .. } => Ok(AngleOrNumber::Number { value }),
             Token::Function(ref name) if name.eq_ignore_ascii_case("calc") => {
                 input.parse_nested_block(|i| CalcNode::parse_angle_or_number(self.0, i))
-            },
+            }
             t => return Err(location.new_unexpected_token_error(t)),
         }
     }
@@ -119,10 +119,10 @@ impl<'a, 'b: 'a, 'i: 'a> ::cssparser::ColorComponentParser<'i> for ColorComponen
             Token::Number { value, .. } => Ok(NumberOrPercentage::Number { value }),
             Token::Percentage { unit_value, .. } => {
                 Ok(NumberOrPercentage::Percentage { unit_value })
-            },
+            }
             Token::Function(ref name) if name.eq_ignore_ascii_case("calc") => {
                 input.parse_nested_block(|i| CalcNode::parse_number_or_percentage(self.0, i))
-            },
+            }
             t => return Err(location.new_unexpected_token_error(t)),
         }
     }
@@ -168,10 +168,10 @@ impl Parse for Color {
                         Err(e.location.new_custom_error(StyleParseErrorKind::ValueError(
                             ValueParseErrorKind::InvalidColor(t),
                         )))
-                    },
+                    }
                     _ => Err(e),
                 }
-            },
+            }
         }
     }
 }
@@ -275,10 +275,10 @@ impl Color {
                 }
                 return parse_hash_color(ident.as_bytes())
                     .map_err(|()| location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
-            },
+            }
             ref t => {
                 return Err(location.new_unexpected_token_error(t.clone()));
-            },
+            }
         };
         if value < 0 {
             return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
@@ -358,11 +358,11 @@ impl Color {
                         Keyword::MozVisitedhyperlinktext => pres_context.mVisitedLinkColor,
                     })
                 })
-            },
+            }
             #[cfg(feature = "gecko")]
             Color::InheritFromBodyQuirk => {
                 _context.map(|context| ComputedColor::rgba(context.device().body_text_color()))
-            },
+            }
         }
     }
 }
@@ -372,7 +372,7 @@ impl ToComputedValue for Color {
 
     fn to_computed_value(&self, context: &Context) -> ComputedColor {
         let result = self.to_computed_color(Some(context)).unwrap();
-        if result.foreground_ratio != 0 {
+        if !result.is_numeric() {
             if let Some(longhand) = context.for_non_inherited_property {
                 if longhand.stores_complex_colors_lossily() {
                     context.rule_cache_conditions.borrow_mut().set_uncacheable();
@@ -383,12 +383,10 @@ impl ToComputedValue for Color {
     }
 
     fn from_computed_value(computed: &ComputedColor) -> Self {
-        if computed.is_numeric() {
-            Color::rgba(computed.color)
-        } else if computed.is_currentcolor() {
-            Color::currentcolor()
-        } else {
-            Color::Complex(*computed)
+        match *computed {
+            ComputedColor::Numeric(color) => Color::rgba(color),
+            ComputedColor::Foreground => Color::currentcolor(),
+            ComputedColor::Complex(..) => Color::Complex(*computed),
         }
     }
 }