1 files changed, 141 insertions, 0 deletions
diff --git a/servo/components/style/values/animated/lists.rs b/servo/components/style/values/animated/lists.rs
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+++ b/servo/components/style/values/animated/lists.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/. */
+
+//! Lists have various ways of being animated, this module implements them.
+//!
+//! See https://drafts.csswg.org/web-animations-1/#animating-properties
+
+/// https://drafts.csswg.org/web-animations-1/#by-computed-value
+pub mod by_computed_value {
+    use crate::values::{
+        animated::{Animate, Procedure},
+        distance::{ComputeSquaredDistance, SquaredDistance},
+    };
+    use std::iter::FromIterator;
+
+    #[allow(missing_docs)]
+    pub fn animate<T, C>(left: &[T], right: &[T], procedure: Procedure) -> Result<C, ()>
+    where
+        T: Animate,
+        C: FromIterator<T>,
+    {
+        if left.len() != right.len() {
+            return Err(());
+        }
+        left.iter()
+            .zip(right.iter())
+            .map(|(left, right)| left.animate(right, procedure))
+            .collect()
+    }
+
+    #[allow(missing_docs)]
+    pub fn squared_distance<T>(left: &[T], right: &[T]) -> Result<SquaredDistance, ()>
+    where
+        T: ComputeSquaredDistance,
+    {
+        if left.len() != right.len() {
+            return Err(());
+        }
+        left.iter()
+            .zip(right.iter())
+            .map(|(left, right)| left.compute_squared_distance(right))
+            .sum()
+    }
+}
+
+/// This is the animation used for some of the types like shadows and filters, where the
+/// interpolation happens with the zero value if one of the sides is not present.
+///
+/// https://drafts.csswg.org/web-animations-1/#animating-shadow-lists
+pub mod with_zero {
+    use crate::values::animated::ToAnimatedZero;
+    use crate::values::{
+        animated::{Animate, Procedure},
+        distance::{ComputeSquaredDistance, SquaredDistance},
+    };
+    use itertools::{EitherOrBoth, Itertools};
+    use std::iter::FromIterator;
+
+    #[allow(missing_docs)]
+    pub fn animate<T, C>(left: &[T], right: &[T], procedure: Procedure) -> Result<C, ()>
+    where
+        T: Animate + Clone + ToAnimatedZero,
+        C: FromIterator<T>,
+    {
+        if procedure == Procedure::Add {
+            return Ok(left.iter().chain(right.iter()).cloned().collect());
+        }
+        left.iter()
+            .zip_longest(right.iter())
+            .map(|it| match it {
+                EitherOrBoth::Both(left, right) => left.animate(right, procedure),
+                EitherOrBoth::Left(left) => left.animate(&left.to_animated_zero()?, procedure),
+                EitherOrBoth::Right(right) => right.to_animated_zero()?.animate(right, procedure),
+            })
+            .collect()
+    }
+
+    #[allow(missing_docs)]
+    pub fn squared_distance<T>(left: &[T], right: &[T]) -> Result<SquaredDistance, ()>
+    where
+        T: ToAnimatedZero + ComputeSquaredDistance,
+    {
+        left.iter()
+            .zip_longest(right.iter())
+            .map(|it| match it {
+                EitherOrBoth::Both(left, right) => left.compute_squared_distance(right),
+                EitherOrBoth::Left(item) | EitherOrBoth::Right(item) => {
+                    item.to_animated_zero()?.compute_squared_distance(item)
+                },
+            })
+            .sum()
+    }
+}
+
+/// https://drafts.csswg.org/web-animations-1/#repeatable-list
+pub mod repeatable_list {
+    use crate::values::{
+        animated::{Animate, Procedure},
+        distance::{ComputeSquaredDistance, SquaredDistance},
+    };
+    use std::iter::FromIterator;
+
+    #[allow(missing_docs)]
+    pub fn animate<T, C>(left: &[T], right: &[T], procedure: Procedure) -> Result<C, ()>
+    where
+        T: Animate,
+        C: FromIterator<T>,
+    {
+        use num_integer::lcm;
+        // If the length of either list is zero, the least common multiple is undefined.
+        if left.is_empty() || right.is_empty() {
+            return Err(());
+        }
+        let len = lcm(left.len(), right.len());
+        left.iter()
+            .cycle()
+            .zip(right.iter().cycle())
+            .take(len)
+            .map(|(left, right)| left.animate(right, procedure))
+            .collect()
+    }
+
+    #[allow(missing_docs)]
+    pub fn squared_distance<T>(left: &[T], right: &[T]) -> Result<SquaredDistance, ()>
+    where
+        T: ComputeSquaredDistance,
+    {
+        use num_integer::lcm;
+        if left.is_empty() || right.is_empty() {
+            return Err(());
+        }
+        let len = lcm(left.len(), right.len());
+        left.iter()
+            .cycle()
+            .zip(right.iter().cycle())
+            .take(len)
+            .map(|(left, right)| left.compute_squared_distance(right))
+            .sum()
+    }
+}