Use generics for background-size property

components/style/values/computed/background.rs

@@ -0,0 +1,52 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Computed types for CSS values related to backgrounds.
+
+use properties::animated_properties::{Animatable, RepeatableListAnimatable};
+use values::computed::length::LengthOrPercentageOrAuto;
+use values::generics::background::BackgroundSize as GenericBackgroundSize;
+
+/// A computed value for the `background-size` property.
+pub type BackgroundSize = GenericBackgroundSize<LengthOrPercentageOrAuto>;
+
+impl RepeatableListAnimatable for BackgroundSize {}
+
+impl Animatable for BackgroundSize {
+    fn add_weighted(&self, other: &Self, self_portion: f64, other_portion: f64) -> Result<Self, ()> {
+        match (self, other) {
+            (
+                &GenericBackgroundSize::Explicit { width: self_width, height: self_height },
+                &GenericBackgroundSize::Explicit { width: other_width, height: other_height },
+            ) => {
+                Ok(GenericBackgroundSize::Explicit {
+                    width: self_width.add_weighted(&other_width, self_portion, other_portion)?,
+                    height: self_height.add_weighted(&other_height, self_portion, other_portion)?,
+                })
+            }
+            _ => Err(()),
+        }
+    }
+
+    #[inline]
+    fn compute_distance(&self, other: &Self) -> Result<f64, ()> {
+        self.compute_squared_distance(other).map(|sd| sd.sqrt())
+    }
+
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<f64, ()> {
+        match (self, other) {
+            (
+                &GenericBackgroundSize::Explicit { width: self_width, height: self_height },
+                &GenericBackgroundSize::Explicit { width: other_width, height: other_height },
+            ) => {
+                Ok(
+                    self_width.compute_squared_distance(&other_width)? +
+                    self_height.compute_squared_distance(&other_height)?
+                )
+            }
+            _ => Err(()),
+        }
+    }
+}