Introduce ToAnimatedValue 🎥

components/style/values/animated/mod.rs

@@ -8,4 +8,83 @@
 //! computed values and need yet another intermediate representation. This
 //! module's raison d'être is to ultimately contain all these types.
 
+use app_units::Au;
+use values::computed::Angle as ComputedAngle;
+use values::specified::url::SpecifiedUrl;
+
 pub mod effects;
+
+/// Conversion between computed values and intermediate values for animations.
+///
+/// Notably, colors are represented as four floats during animations.
+pub trait ToAnimatedValue {
+    /// The type of the animated value.
+    type AnimatedValue;
+
+    /// Converts this value to an animated value.
+    fn to_animated_value(self) -> Self::AnimatedValue;
+
+    /// Converts back an animated value into a computed value.
+    fn from_animated_value(animated: Self::AnimatedValue) -> Self;
+}
+
+impl<T> ToAnimatedValue for Option<T>
+where
+    T: ToAnimatedValue,
+{
+    type AnimatedValue = Option<<T as ToAnimatedValue>::AnimatedValue>;
+
+    #[inline]
+    fn to_animated_value(self) -> Self::AnimatedValue {
+        self.map(T::to_animated_value)
+    }
+
+    #[inline]
+    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
+        animated.map(T::from_animated_value)
+    }
+}
+
+impl<T> ToAnimatedValue for Vec<T>
+where
+    T: ToAnimatedValue,
+{
+    type AnimatedValue = Vec<<T as ToAnimatedValue>::AnimatedValue>;
+
+    #[inline]
+    fn to_animated_value(self) -> Self::AnimatedValue {
+        self.into_iter().map(T::to_animated_value).collect()
+    }
+
+    #[inline]
+    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
+        animated.into_iter().map(T::from_animated_value).collect()
+    }
+}
+
+/// Marker trait for computed values with the same representation during animations.
+pub trait AnimatedValueAsComputed {}
+
+impl AnimatedValueAsComputed for Au {}
+impl AnimatedValueAsComputed for ComputedAngle {}
+impl AnimatedValueAsComputed for SpecifiedUrl {}
+impl AnimatedValueAsComputed for bool {}
+impl AnimatedValueAsComputed for f32 {}
+
+impl<T> ToAnimatedValue for T
+where
+    T: AnimatedValueAsComputed,
+{
+    type AnimatedValue = Self;
+
+    #[inline]
+    fn to_animated_value(self) -> Self {
+        self
+    }
+
+    #[inline]
+    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
+        animated
+    }
+}
+