1 files changed, 138 insertions, 0 deletions
diff --git a/servo/components/style/values/distance.rs b/servo/components/style/values/distance.rs
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+++ b/servo/components/style/values/distance.rs
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+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! Machinery to compute distances between animatable values.
+
+use app_units::Au;
+use euclid::default::Size2D;
+use std::iter::Sum;
+use std::ops::Add;
+
+/// A trait to compute squared distances between two animatable values.
+///
+/// This trait is derivable with `#[derive(ComputeSquaredDistance)]`. The derived
+/// implementation uses a `match` expression with identical patterns for both
+/// `self` and `other`, calling `ComputeSquaredDistance::compute_squared_distance`
+/// on each fields of the values.
+///
+/// If a variant is annotated with `#[animation(error)]`, the corresponding
+/// `match` arm returns an error.
+///
+/// Trait bounds for type parameter `Foo` can be opted out of with
+/// `#[animation(no_bound(Foo))]` on the type definition, trait bounds for
+/// fields can be opted into with `#[distance(field_bound)]` on the field.
+pub trait ComputeSquaredDistance {
+    /// Computes the squared distance between two animatable values.
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()>;
+}
+
+/// A distance between two animatable values.
+#[derive(Add, Clone, Copy, Debug, From)]
+pub struct SquaredDistance {
+    value: f64,
+}
+
+impl SquaredDistance {
+    /// Returns a squared distance from its square root.
+    #[inline]
+    pub fn from_sqrt(sqrt: f64) -> Self {
+        Self { value: sqrt * sqrt }
+    }
+}
+
+impl ComputeSquaredDistance for u16 {
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        Ok(SquaredDistance::from_sqrt(
+            ((*self as f64) - (*other as f64)).abs(),
+        ))
+    }
+}
+
+impl ComputeSquaredDistance for i16 {
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        Ok(SquaredDistance::from_sqrt((*self - *other).abs() as f64))
+    }
+}
+
+impl ComputeSquaredDistance for i32 {
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        Ok(SquaredDistance::from_sqrt((*self - *other).abs() as f64))
+    }
+}
+
+impl ComputeSquaredDistance for f32 {
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        Ok(SquaredDistance::from_sqrt((*self - *other).abs() as f64))
+    }
+}
+
+impl ComputeSquaredDistance for f64 {
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        Ok(SquaredDistance::from_sqrt((*self - *other).abs()))
+    }
+}
+
+impl ComputeSquaredDistance for Au {
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        self.0.compute_squared_distance(&other.0)
+    }
+}
+
+impl<T> ComputeSquaredDistance for Box<T>
+where
+    T: ComputeSquaredDistance,
+{
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        (**self).compute_squared_distance(&**other)
+    }
+}
+
+impl<T> ComputeSquaredDistance for Option<T>
+where
+    T: ComputeSquaredDistance,
+{
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        match (self.as_ref(), other.as_ref()) {
+            (Some(this), Some(other)) => this.compute_squared_distance(other),
+            (None, None) => Ok(SquaredDistance::from_sqrt(0.)),
+            _ => Err(()),
+        }
+    }
+}
+
+impl<T> ComputeSquaredDistance for Size2D<T>
+where
+    T: ComputeSquaredDistance,
+{
+    #[inline]
+    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
+        Ok(self.width.compute_squared_distance(&other.width)? +
+            self.height.compute_squared_distance(&other.height)?)
+    }
+}
+
+impl SquaredDistance {
+    /// Returns the square root of this squared distance.
+    #[inline]
+    pub fn sqrt(self) -> f64 {
+        self.value.sqrt()
+    }
+}
+
+impl Sum for SquaredDistance {
+    fn sum<I>(iter: I) -> Self
+    where
+        I: Iterator<Item = Self>,
+    {
+        iter.fold(SquaredDistance::from_sqrt(0.), Add::add)
+    }
+}