1 files changed, 165 insertions, 0 deletions
diff --git a/servo/components/style/values/animated/grid.rs b/servo/components/style/values/animated/grid.rs
new file mode 100644
index 0000000000..04f1a2fcaa
--- /dev/null
+++ b/servo/components/style/values/animated/grid.rs
@@ -0,0 +1,165 @@
+/* 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/. */
+
+//! Animation implementation for various grid-related types.
+
+// Note: we can implement Animate on their generic types directly, but in this case we need to
+// make sure two trait bounds, L: Clone and I: PartialEq, are satisfied on almost all the
+// grid-related types and their other trait implementations because Animate needs them. So in
+// order to avoid adding these two trait bounds (or maybe more..) everywhere, we implement
+// Animate for the computed types, instead of the generic types.
+
+use super::{Animate, Procedure, ToAnimatedZero};
+use crate::values::computed::Integer;
+use crate::values::computed::LengthPercentage;
+use crate::values::computed::{GridTemplateComponent, TrackList, TrackSize};
+use crate::values::distance::{ComputeSquaredDistance, SquaredDistance};
+use crate::values::generics::grid as generics;
+
+fn discrete<T: Clone>(from: &T, to: &T, procedure: Procedure) -> Result<T, ()> {
+    if let Procedure::Interpolate { progress } = procedure {
+        Ok(if progress < 0.5 {
+            from.clone()
+        } else {
+            to.clone()
+        })
+    } else {
+        // The discrete animation is not additive, so per spec [1] we should use the |from|, which
+        // is the underlying value. However this mismatches our animation mechanism (see
+        // composite_endpoint() in servo/ports/geckolib/glues.rs), which uses the effect value
+        // (i.e. |to| value here) [2]. So in order to match the behavior of other properties and
+        // other browsers, we use |to| value for addition and accumulation, i.e. Vresult = Vb.
+        //
+        // [1] https://drafts.csswg.org/css-values-4/#not-additive
+        // [2] https://github.com/w3c/csswg-drafts/issues/9070
+        Ok(to.clone())
+    }
+}
+
+fn animate_with_discrete_fallback<T: Animate + Clone>(
+    from: &T,
+    to: &T,
+    procedure: Procedure,
+) -> Result<T, ()> {
+    from.animate(to, procedure)
+        .or_else(|_| discrete(from, to, procedure))
+}
+
+impl Animate for TrackSize {
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        match (self, other) {
+            (&generics::TrackSize::Breadth(ref from), &generics::TrackSize::Breadth(ref to)) => {
+                animate_with_discrete_fallback(from, to, procedure)
+                    .map(generics::TrackSize::Breadth)
+            },
+            (
+                &generics::TrackSize::Minmax(ref from_min, ref from_max),
+                &generics::TrackSize::Minmax(ref to_min, ref to_max),
+            ) => Ok(generics::TrackSize::Minmax(
+                animate_with_discrete_fallback(from_min, to_min, procedure)?,
+                animate_with_discrete_fallback(from_max, to_max, procedure)?,
+            )),
+            (
+                &generics::TrackSize::FitContent(ref from),
+                &generics::TrackSize::FitContent(ref to),
+            ) => animate_with_discrete_fallback(from, to, procedure)
+                .map(generics::TrackSize::FitContent),
+            (_, _) => discrete(self, other, procedure),
+        }
+    }
+}
+
+impl Animate for generics::TrackRepeat<LengthPercentage, Integer> {
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        // If the keyword, auto-fit/fill, is the same it can result in different
+        // number of tracks. For both auto-fit/fill, the number of columns isn't
+        // known until you do layout since it depends on the container size, item
+        // placement and other factors, so we cannot do the correct interpolation
+        // by computed values. Therefore, return Err(()) if it's keywords. If it
+        // is Number, we support animation only if the count is the same and the
+        // length of track_sizes is the same.
+        // https://github.com/w3c/csswg-drafts/issues/3503
+        match (&self.count, &other.count) {
+            (&generics::RepeatCount::Number(from), &generics::RepeatCount::Number(to))
+                if from == to =>
+            {
+                ()
+            },
+            (_, _) => return Err(()),
+        }
+
+        let count = self.count;
+        let track_sizes = super::lists::by_computed_value::animate(
+            &self.track_sizes,
+            &other.track_sizes,
+            procedure,
+        )?;
+
+        // The length of |line_names| is always 0 or N+1, where N is the length
+        // of |track_sizes|. Besides, <line-names> is always discrete.
+        let line_names = discrete(&self.line_names, &other.line_names, procedure)?;
+
+        Ok(generics::TrackRepeat {
+            count,
+            line_names,
+            track_sizes,
+        })
+    }
+}
+
+impl Animate for TrackList {
+    // Based on https://github.com/w3c/csswg-drafts/issues/3201:
+    // 1. Check interpolation type per track, so we need to handle discrete animations
+    //    in TrackSize, so any Err(()) returned from TrackSize doesn't make all TrackSize
+    //    fallback to discrete animation.
+    // 2. line-names is always discrete.
+    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
+        if self.values.len() != other.values.len() {
+            return Err(());
+        }
+
+        if self.is_explicit() != other.is_explicit() {
+            return Err(());
+        }
+
+        // For now, repeat(auto-fill/auto-fit, ...) is not animatable.
+        // TrackRepeat will return Err(()) if we use keywords. Therefore, we can
+        // early return here to avoid traversing |values| in <auto-track-list>.
+        // This may be updated in the future.
+        // https://github.com/w3c/csswg-drafts/issues/3503
+        if self.has_auto_repeat() || other.has_auto_repeat() {
+            return Err(());
+        }
+
+        let values =
+            super::lists::by_computed_value::animate(&self.values, &other.values, procedure)?;
+
+        // The length of |line_names| is always 0 or N+1, where N is the length
+        // of |track_sizes|. Besides, <line-names> is always discrete.
+        let line_names = discrete(&self.line_names, &other.line_names, procedure)?;
+
+        Ok(TrackList {
+            values,
+            line_names,
+            auto_repeat_index: self.auto_repeat_index,
+        })
+    }
+}
+
+impl ComputeSquaredDistance for GridTemplateComponent {
+    #[inline]
+    fn compute_squared_distance(&self, _other: &Self) -> Result<SquaredDistance, ()> {
+        // TODO: Bug 1518585, we should implement ComputeSquaredDistance.
+        Err(())
+    }
+}
+
+impl ToAnimatedZero for GridTemplateComponent {
+    #[inline]
+    fn to_animated_zero(&self) -> Result<Self, ()> {
+        // It's not clear to get a zero grid track list based on the current definition
+        // of spec, so we return Err(()) directly.
+        Err(())
+    }
+}