Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1410 insertions, 0 deletions

diff --git a/servo/components/style/animation.rs b/servo/components/style/animation.rs
new file mode 100644
index 0000000000..f3c70fef6e
--- /dev/null
+++ b/servo/components/style/animation.rs
@@ -0,0 +1,1410 @@
+/* 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/. */
+
+//! CSS transitions and animations.
+
+// NOTE(emilio): This code isn't really executed in Gecko, but we don't want to
+// compile it out so that people remember it exists.
+
+use crate::context::{CascadeInputs, SharedStyleContext};
+use crate::dom::{OpaqueNode, TDocument, TElement, TNode};
+use crate::properties::animated_properties::{AnimationValue, AnimationValueMap};
+use crate::properties::longhands::animation_direction::computed_value::single_value::T as AnimationDirection;
+use crate::properties::longhands::animation_fill_mode::computed_value::single_value::T as AnimationFillMode;
+use crate::properties::longhands::animation_play_state::computed_value::single_value::T as AnimationPlayState;
+use crate::properties::AnimationDeclarations;
+use crate::properties::{
+    ComputedValues, Importance, LonghandId, LonghandIdSet, PropertyDeclarationBlock,
+    PropertyDeclarationId,
+};
+use crate::rule_tree::CascadeLevel;
+use crate::selector_parser::PseudoElement;
+use crate::shared_lock::{Locked, SharedRwLock};
+use crate::style_resolver::StyleResolverForElement;
+use crate::stylesheets::keyframes_rule::{KeyframesAnimation, KeyframesStep, KeyframesStepValue};
+use crate::stylesheets::layer_rule::LayerOrder;
+use crate::values::animated::{Animate, Procedure};
+use crate::values::computed::{Time, TimingFunction};
+use crate::values::generics::box_::AnimationIterationCount;
+use crate::values::generics::easing::BeforeFlag;
+use crate::Atom;
+use fxhash::FxHashMap;
+use parking_lot::RwLock;
+use servo_arc::Arc;
+use std::fmt;
+
+/// Represents an animation for a given property.
+#[derive(Clone, Debug, MallocSizeOf)]
+pub struct PropertyAnimation {
+    /// The value we are animating from.
+    from: AnimationValue,
+
+    /// The value we are animating to.
+    to: AnimationValue,
+
+    /// The timing function of this `PropertyAnimation`.
+    timing_function: TimingFunction,
+
+    /// The duration of this `PropertyAnimation` in seconds.
+    pub duration: f64,
+}
+
+impl PropertyAnimation {
+    /// Returns the given property longhand id.
+    pub fn property_id(&self) -> LonghandId {
+        debug_assert_eq!(self.from.id(), self.to.id());
+        self.from.id()
+    }
+
+    fn from_longhand(
+        longhand: LonghandId,
+        timing_function: TimingFunction,
+        duration: Time,
+        old_style: &ComputedValues,
+        new_style: &ComputedValues,
+    ) -> Option<PropertyAnimation> {
+        // FIXME(emilio): Handle the case where old_style and new_style's writing mode differ.
+        let longhand = longhand.to_physical(new_style.writing_mode);
+        let from = AnimationValue::from_computed_values(longhand, old_style)?;
+        let to = AnimationValue::from_computed_values(longhand, new_style)?;
+        let duration = duration.seconds() as f64;
+
+        if from == to || duration == 0.0 {
+            return None;
+        }
+
+        Some(PropertyAnimation {
+            from,
+            to,
+            timing_function,
+            duration,
+        })
+    }
+
+    /// The output of the timing function given the progress ration of this animation.
+    fn timing_function_output(&self, progress: f64) -> f64 {
+        let epsilon = 1. / (200. * self.duration);
+        // FIXME: Need to set the before flag correctly.
+        // In order to get the before flag, we have to know the current animation phase
+        // and whether the iteration is reversed. For now, we skip this calculation
+        // by treating as if the flag is unset at all times.
+        // https://drafts.csswg.org/css-easing/#step-timing-function-algo
+        self.timing_function
+            .calculate_output(progress, BeforeFlag::Unset, epsilon)
+    }
+
+    /// Update the given animation at a given point of progress.
+    fn calculate_value(&self, progress: f64) -> Result<AnimationValue, ()> {
+        let procedure = Procedure::Interpolate {
+            progress: self.timing_function_output(progress),
+        };
+        self.from.animate(&self.to, procedure)
+    }
+}
+
+/// This structure represents the state of an animation.
+#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
+pub enum AnimationState {
+    /// The animation has been created, but is not running yet. This state
+    /// is also used when an animation is still in the first delay phase.
+    Pending,
+    /// This animation is currently running.
+    Running,
+    /// This animation is paused. The inner field is the percentage of progress
+    /// when it was paused, from 0 to 1.
+    Paused(f64),
+    /// This animation has finished.
+    Finished,
+    /// This animation has been canceled.
+    Canceled,
+}
+
+impl AnimationState {
+    /// Whether or not this state requires its owning animation to be ticked.
+    fn needs_to_be_ticked(&self) -> bool {
+        *self == AnimationState::Running || *self == AnimationState::Pending
+    }
+}
+
+/// This structure represents a keyframes animation current iteration state.
+///
+/// If the iteration count is infinite, there's no other state, otherwise we
+/// have to keep track the current iteration and the max iteration count.
+#[derive(Clone, Debug, MallocSizeOf)]
+pub enum KeyframesIterationState {
+    /// Infinite iterations with the current iteration count.
+    Infinite(f64),
+    /// Current and max iterations.
+    Finite(f64, f64),
+}
+
+/// A temporary data structure used when calculating ComputedKeyframes for an
+/// animation. This data structure is used to collapse information for steps
+/// which may be spread across multiple keyframe declarations into a single
+/// instance per `start_percentage`.
+struct IntermediateComputedKeyframe {
+    declarations: PropertyDeclarationBlock,
+    timing_function: Option<TimingFunction>,
+    start_percentage: f32,
+}
+
+impl IntermediateComputedKeyframe {
+    fn new(start_percentage: f32) -> Self {
+        IntermediateComputedKeyframe {
+            declarations: PropertyDeclarationBlock::new(),
+            timing_function: None,
+            start_percentage,
+        }
+    }
+
+    /// Walk through all keyframe declarations and combine all declarations with the
+    /// same `start_percentage` into individual `IntermediateComputedKeyframe`s.
+    fn generate_for_keyframes(
+        animation: &KeyframesAnimation,
+        context: &SharedStyleContext,
+        base_style: &ComputedValues,
+    ) -> Vec<Self> {
+        let mut intermediate_steps: Vec<Self> = Vec::with_capacity(animation.steps.len());
+        let mut current_step = IntermediateComputedKeyframe::new(0.);
+        for step in animation.steps.iter() {
+            let start_percentage = step.start_percentage.0;
+            if start_percentage != current_step.start_percentage {
+                let new_step = IntermediateComputedKeyframe::new(start_percentage);
+                intermediate_steps.push(std::mem::replace(&mut current_step, new_step));
+            }
+
+            current_step.update_from_step(step, context, base_style);
+        }
+        intermediate_steps.push(current_step);
+
+        // We should always have a first and a last step, even if these are just
+        // generated by KeyframesStepValue::ComputedValues.
+        debug_assert!(intermediate_steps.first().unwrap().start_percentage == 0.);
+        debug_assert!(intermediate_steps.last().unwrap().start_percentage == 1.);
+
+        intermediate_steps
+    }
+
+    fn update_from_step(
+        &mut self,
+        step: &KeyframesStep,
+        context: &SharedStyleContext,
+        base_style: &ComputedValues,
+    ) {
+        // Each keyframe declaration may optionally specify a timing function, falling
+        // back to the one defined global for the animation.
+        let guard = &context.guards.author;
+        if let Some(timing_function) = step.get_animation_timing_function(&guard) {
+            self.timing_function = Some(timing_function.to_computed_value_without_context());
+        }
+
+        let block = match step.value {
+            KeyframesStepValue::ComputedValues => return,
+            KeyframesStepValue::Declarations { ref block } => block,
+        };
+
+        // Filter out !important, non-animatable properties, and the
+        // 'display' property (which is only animatable from SMIL).
+        let guard = block.read_with(&guard);
+        for declaration in guard.normal_declaration_iter() {
+            if let PropertyDeclarationId::Longhand(id) = declaration.id() {
+                if id == LonghandId::Display {
+                    continue;
+                }
+
+                if !id.is_animatable() {
+                    continue;
+                }
+            }
+
+            self.declarations.push(
+                declaration.to_physical(base_style.writing_mode),
+                Importance::Normal,
+            );
+        }
+    }
+
+    fn resolve_style<E>(
+        self,
+        element: E,
+        context: &SharedStyleContext,
+        base_style: &Arc<ComputedValues>,
+        resolver: &mut StyleResolverForElement<E>,
+    ) -> Arc<ComputedValues>
+    where
+        E: TElement,
+    {
+        if !self.declarations.any_normal() {
+            return base_style.clone();
+        }
+
+        let document = element.as_node().owner_doc();
+        let locked_block = Arc::new(document.shared_lock().wrap(self.declarations));
+        let mut important_rules_changed = false;
+        let rule_node = base_style.rules().clone();
+        let new_node = context.stylist.rule_tree().update_rule_at_level(
+            CascadeLevel::Animations,
+            LayerOrder::root(),
+            Some(locked_block.borrow_arc()),
+            &rule_node,
+            &context.guards,
+            &mut important_rules_changed,
+        );
+
+        if new_node.is_none() {
+            return base_style.clone();
+        }
+
+        let inputs = CascadeInputs {
+            rules: new_node,
+            visited_rules: base_style.visited_rules().cloned(),
+            flags: base_style.flags.for_cascade_inputs(),
+        };
+        resolver
+            .cascade_style_and_visited_with_default_parents(inputs)
+            .0
+    }
+}
+
+/// A single computed keyframe for a CSS Animation.
+#[derive(Clone, MallocSizeOf)]
+struct ComputedKeyframe {
+    /// The timing function to use for transitions between this step
+    /// and the next one.
+    timing_function: TimingFunction,
+
+    /// The starting percentage (a number between 0 and 1) which represents
+    /// at what point in an animation iteration this step is.
+    start_percentage: f32,
+
+    /// The animation values to transition to and from when processing this
+    /// keyframe animation step.
+    values: Vec<AnimationValue>,
+}
+
+impl ComputedKeyframe {
+    fn generate_for_keyframes<E>(
+        element: E,
+        animation: &KeyframesAnimation,
+        context: &SharedStyleContext,
+        base_style: &Arc<ComputedValues>,
+        default_timing_function: TimingFunction,
+        resolver: &mut StyleResolverForElement<E>,
+    ) -> Vec<Self>
+    where
+        E: TElement,
+    {
+        let mut animating_properties = LonghandIdSet::new();
+        for property in animation.properties_changed.iter() {
+            debug_assert!(property.is_animatable());
+            animating_properties.insert(property.to_physical(base_style.writing_mode));
+        }
+
+        let animation_values_from_style: Vec<AnimationValue> = animating_properties
+            .iter()
+            .map(|property| {
+                AnimationValue::from_computed_values(property, &**base_style)
+                    .expect("Unexpected non-animatable property.")
+            })
+            .collect();
+
+        let intermediate_steps =
+            IntermediateComputedKeyframe::generate_for_keyframes(animation, context, base_style);
+
+        let mut computed_steps: Vec<Self> = Vec::with_capacity(intermediate_steps.len());
+        for (step_index, step) in intermediate_steps.into_iter().enumerate() {
+            let start_percentage = step.start_percentage;
+            let properties_changed_in_step = step.declarations.longhands().clone();
+            let step_timing_function = step.timing_function.clone();
+            let step_style = step.resolve_style(element, context, base_style, resolver);
+            let timing_function =
+                step_timing_function.unwrap_or_else(|| default_timing_function.clone());
+
+            let values = {
+                // If a value is not set in a property declaration we use the value from
+                // the style for the first and last keyframe. For intermediate ones, we
+                // use the value from the previous keyframe.
+                //
+                // TODO(mrobinson): According to the spec, we should use an interpolated
+                // value for properties missing from keyframe declarations.
+                let default_values = if start_percentage == 0. || start_percentage == 1.0 {
+                    &animation_values_from_style
+                } else {
+                    debug_assert!(step_index != 0);
+                    &computed_steps[step_index - 1].values
+                };
+
+                // For each property that is animating, pull the value from the resolved
+                // style for this step if it's in one of the declarations. Otherwise, we
+                // use the default value from the set we calculated above.
+                animating_properties
+                    .iter()
+                    .zip(default_values.iter())
+                    .map(|(longhand, default_value)| {
+                        if properties_changed_in_step.contains(longhand) {
+                            AnimationValue::from_computed_values(longhand, &step_style)
+                                .unwrap_or_else(|| default_value.clone())
+                        } else {
+                            default_value.clone()
+                        }
+                    })
+                    .collect()
+            };
+
+            computed_steps.push(ComputedKeyframe {
+                timing_function,
+                start_percentage,
+                values,
+            });
+        }
+        computed_steps
+    }
+}
+
+/// A CSS Animation
+#[derive(Clone, MallocSizeOf)]
+pub struct Animation {
+    /// The name of this animation as defined by the style.
+    pub name: Atom,
+
+    /// The properties that change in this animation.
+    properties_changed: LonghandIdSet,
+
+    /// The computed style for each keyframe of this animation.
+    computed_steps: Vec<ComputedKeyframe>,
+
+    /// The time this animation started at, which is the current value of the animation
+    /// timeline when this animation was created plus any animation delay.
+    pub started_at: f64,
+
+    /// The duration of this animation.
+    pub duration: f64,
+
+    /// The delay of the animation.
+    pub delay: f64,
+
+    /// The `animation-fill-mode` property of this animation.
+    pub fill_mode: AnimationFillMode,
+
+    /// The current iteration state for the animation.
+    pub iteration_state: KeyframesIterationState,
+
+    /// Whether this animation is paused.
+    pub state: AnimationState,
+
+    /// The declared animation direction of this animation.
+    pub direction: AnimationDirection,
+
+    /// The current animation direction. This can only be `normal` or `reverse`.
+    pub current_direction: AnimationDirection,
+
+    /// The original cascade style, needed to compute the generated keyframes of
+    /// the animation.
+    #[ignore_malloc_size_of = "ComputedValues"]
+    pub cascade_style: Arc<ComputedValues>,
+
+    /// Whether or not this animation is new and or has already been tracked
+    /// by the script thread.
+    pub is_new: bool,
+}
+
+impl Animation {
+    /// Whether or not this animation is cancelled by changes from a new style.
+    fn is_cancelled_in_new_style(&self, new_style: &Arc<ComputedValues>) -> bool {
+        let new_ui = new_style.get_ui();
+        let index = new_ui
+            .animation_name_iter()
+            .position(|animation_name| Some(&self.name) == animation_name.as_atom());
+        let index = match index {
+            Some(index) => index,
+            None => return true,
+        };
+
+        new_ui.animation_duration_mod(index).seconds() == 0.
+    }
+
+    /// Given the current time, advances this animation to the next iteration,
+    /// updates times, and then toggles the direction if appropriate. Otherwise
+    /// does nothing. Returns true if this animation has iterated.
+    pub fn iterate_if_necessary(&mut self, time: f64) -> bool {
+        if !self.iteration_over(time) {
+            return false;
+        }
+
+        // Only iterate animations that are currently running.
+        if self.state != AnimationState::Running {
+            return false;
+        }
+
+        if self.on_last_iteration() {
+            return false;
+        }
+
+        self.iterate();
+        true
+    }
+
+    fn iterate(&mut self) {
+        debug_assert!(!self.on_last_iteration());
+
+        if let KeyframesIterationState::Finite(ref mut current, max) = self.iteration_state {
+            *current = (*current + 1.).min(max);
+        }
+
+        if let AnimationState::Paused(ref mut progress) = self.state {
+            debug_assert!(*progress > 1.);
+            *progress -= 1.;
+        }
+
+        // Update the next iteration direction if applicable.
+        self.started_at += self.duration;
+        match self.direction {
+            AnimationDirection::Alternate | AnimationDirection::AlternateReverse => {
+                self.current_direction = match self.current_direction {
+                    AnimationDirection::Normal => AnimationDirection::Reverse,
+                    AnimationDirection::Reverse => AnimationDirection::Normal,
+                    _ => unreachable!(),
+                };
+            },
+            _ => {},
+        }
+    }
+
+    /// A number (> 0 and <= 1) which represents the fraction of a full iteration
+    /// that the current iteration of the animation lasts. This will be less than 1
+    /// if the current iteration is the fractional remainder of a non-integral
+    /// iteration count.
+    pub fn current_iteration_end_progress(&self) -> f64 {
+        match self.iteration_state {
+            KeyframesIterationState::Finite(current, max) => (max - current).min(1.),
+            KeyframesIterationState::Infinite(_) => 1.,
+        }
+    }
+
+    /// The duration of the current iteration of this animation which may be less
+    /// than the animation duration if it has a non-integral iteration count.
+    pub fn current_iteration_duration(&self) -> f64 {
+        self.current_iteration_end_progress() * self.duration
+    }
+
+    /// Whether or not the current iteration is over. Note that this method assumes that
+    /// the animation is still running.
+    fn iteration_over(&self, time: f64) -> bool {
+        time > (self.started_at + self.current_iteration_duration())
+    }
+
+    /// Assuming this animation is running, whether or not it is on the last iteration.
+    fn on_last_iteration(&self) -> bool {
+        match self.iteration_state {
+            KeyframesIterationState::Finite(current, max) => current >= (max - 1.),
+            KeyframesIterationState::Infinite(_) => false,
+        }
+    }
+
+    /// Whether or not this animation has finished at the provided time. This does
+    /// not take into account canceling i.e. when an animation or transition is
+    /// canceled due to changes in the style.
+    pub fn has_ended(&self, time: f64) -> bool {
+        if !self.on_last_iteration() {
+            return false;
+        }
+
+        let progress = match self.state {
+            AnimationState::Finished => return true,
+            AnimationState::Paused(progress) => progress,
+            AnimationState::Running => (time - self.started_at) / self.duration,
+            AnimationState::Pending | AnimationState::Canceled => return false,
+        };
+
+        progress >= self.current_iteration_end_progress()
+    }
+
+    /// Updates the appropiate state from other animation.
+    ///
+    /// This happens when an animation is re-submitted to layout, presumably
+    /// because of an state change.
+    ///
+    /// There are some bits of state we can't just replace, over all taking in
+    /// account times, so here's that logic.
+    pub fn update_from_other(&mut self, other: &Self, now: f64) {
+        use self::AnimationState::*;
+
+        debug!(
+            "KeyframesAnimationState::update_from_other({:?}, {:?})",
+            self, other
+        );
+
+        // NB: We shall not touch the started_at field, since we don't want to
+        // restart the animation.
+        let old_started_at = self.started_at;
+        let old_duration = self.duration;
+        let old_direction = self.current_direction;
+        let old_state = self.state.clone();
+        let old_iteration_state = self.iteration_state.clone();
+
+        *self = other.clone();
+
+        self.started_at = old_started_at;
+        self.current_direction = old_direction;
+
+        // Don't update the iteration count, just the iteration limit.
+        // TODO: see how changing the limit affects rendering in other browsers.
+        // We might need to keep the iteration count even when it's infinite.
+        match (&mut self.iteration_state, old_iteration_state) {
+            (
+                &mut KeyframesIterationState::Finite(ref mut iters, _),
+                KeyframesIterationState::Finite(old_iters, _),
+            ) => *iters = old_iters,
+            _ => {},
+        }
+
+        // Don't pause or restart animations that should remain finished.
+        // We call mem::replace because `has_ended(...)` looks at `Animation::state`.
+        let new_state = std::mem::replace(&mut self.state, Running);
+        if old_state == Finished && self.has_ended(now) {
+            self.state = Finished;
+        } else {
+            self.state = new_state;
+        }
+
+        // If we're unpausing the animation, fake the start time so we seem to
+        // restore it.
+        //
+        // If the animation keeps paused, keep the old value.
+        //
+        // If we're pausing the animation, compute the progress value.
+        match (&mut self.state, &old_state) {
+            (&mut Pending, &Paused(progress)) => {
+                self.started_at = now - (self.duration * progress);
+            },
+            (&mut Paused(ref mut new), &Paused(old)) => *new = old,
+            (&mut Paused(ref mut progress), &Running) => {
+                *progress = (now - old_started_at) / old_duration
+            },
+            _ => {},
+        }
+
+        // Try to detect when we should skip straight to the running phase to
+        // avoid sending multiple animationstart events.
+        if self.state == Pending && self.started_at <= now && old_state != Pending {
+            self.state = Running;
+        }
+    }
+
+    /// Fill in an `AnimationValueMap` with values calculated from this animation at
+    /// the given time value.
+    fn get_property_declaration_at_time(&self, now: f64, map: &mut AnimationValueMap) {
+        debug_assert!(!self.computed_steps.is_empty());
+
+        let total_progress = match self.state {
+            AnimationState::Running | AnimationState::Pending | AnimationState::Finished => {
+                (now - self.started_at) / self.duration
+            },
+            AnimationState::Paused(progress) => progress,
+            AnimationState::Canceled => return,
+        };
+
+        if total_progress < 0. &&
+            self.fill_mode != AnimationFillMode::Backwards &&
+            self.fill_mode != AnimationFillMode::Both
+        {
+            return;
+        }
+        if self.has_ended(now) &&
+            self.fill_mode != AnimationFillMode::Forwards &&
+            self.fill_mode != AnimationFillMode::Both
+        {
+            return;
+        }
+        let total_progress = total_progress
+            .min(self.current_iteration_end_progress())
+            .max(0.0);
+
+        // Get the indices of the previous (from) keyframe and the next (to) keyframe.
+        let next_keyframe_index;
+        let prev_keyframe_index;
+        let num_steps = self.computed_steps.len();
+        match self.current_direction {
+            AnimationDirection::Normal => {
+                next_keyframe_index = self
+                    .computed_steps
+                    .iter()
+                    .position(|step| total_progress as f32 <= step.start_percentage);
+                prev_keyframe_index = next_keyframe_index
+                    .and_then(|pos| if pos != 0 { Some(pos - 1) } else { None })
+                    .unwrap_or(0);
+            },
+            AnimationDirection::Reverse => {
+                next_keyframe_index = self
+                    .computed_steps
+                    .iter()
+                    .rev()
+                    .position(|step| total_progress as f32 <= 1. - step.start_percentage)
+                    .map(|pos| num_steps - pos - 1);
+                prev_keyframe_index = next_keyframe_index
+                    .and_then(|pos| {
+                        if pos != num_steps - 1 {
+                            Some(pos + 1)
+                        } else {
+                            None
+                        }
+                    })
+                    .unwrap_or(num_steps - 1)
+            },
+            _ => unreachable!(),
+        }
+
+        debug!(
+            "Animation::get_property_declaration_at_time: keyframe from {:?} to {:?}",
+            prev_keyframe_index, next_keyframe_index
+        );
+
+        let prev_keyframe = &self.computed_steps[prev_keyframe_index];
+        let next_keyframe = match next_keyframe_index {
+            Some(index) => &self.computed_steps[index],
+            None => return,
+        };
+
+        // If we only need to take into account one keyframe, then exit early
+        // in order to avoid doing more work.
+        let mut add_declarations_to_map = |keyframe: &ComputedKeyframe| {
+            for value in keyframe.values.iter() {
+                map.insert(value.id(), value.clone());
+            }
+        };
+        if total_progress <= 0.0 {
+            add_declarations_to_map(&prev_keyframe);
+            return;
+        }
+        if total_progress >= 1.0 {
+            add_declarations_to_map(&next_keyframe);
+            return;
+        }
+
+        let percentage_between_keyframes =
+            (next_keyframe.start_percentage - prev_keyframe.start_percentage).abs() as f64;
+        let duration_between_keyframes = percentage_between_keyframes * self.duration;
+        let direction_aware_prev_keyframe_start_percentage = match self.current_direction {
+            AnimationDirection::Normal => prev_keyframe.start_percentage as f64,
+            AnimationDirection::Reverse => 1. - prev_keyframe.start_percentage as f64,
+            _ => unreachable!(),
+        };
+        let progress_between_keyframes = (total_progress -
+            direction_aware_prev_keyframe_start_percentage) /
+            percentage_between_keyframes;
+
+        for (from, to) in prev_keyframe.values.iter().zip(next_keyframe.values.iter()) {
+            let animation = PropertyAnimation {
+                from: from.clone(),
+                to: to.clone(),
+                timing_function: prev_keyframe.timing_function.clone(),
+                duration: duration_between_keyframes as f64,
+            };
+
+            if let Ok(value) = animation.calculate_value(progress_between_keyframes) {
+                map.insert(value.id(), value);
+            }
+        }
+    }
+}
+
+impl fmt::Debug for Animation {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Animation")
+            .field("name", &self.name)
+            .field("started_at", &self.started_at)
+            .field("duration", &self.duration)
+            .field("delay", &self.delay)
+            .field("iteration_state", &self.iteration_state)
+            .field("state", &self.state)
+            .field("direction", &self.direction)
+            .field("current_direction", &self.current_direction)
+            .field("cascade_style", &())
+            .finish()
+    }
+}
+
+/// A CSS Transition
+#[derive(Clone, Debug, MallocSizeOf)]
+pub struct Transition {
+    /// The start time of this transition, which is the current value of the animation
+    /// timeline when this transition was created plus any animation delay.
+    pub start_time: f64,
+
+    /// The delay used for this transition.
+    pub delay: f64,
+
+    /// The internal style `PropertyAnimation` for this transition.
+    pub property_animation: PropertyAnimation,
+
+    /// The state of this transition.
+    pub state: AnimationState,
+
+    /// Whether or not this transition is new and or has already been tracked
+    /// by the script thread.
+    pub is_new: bool,
+
+    /// If this `Transition` has been replaced by a new one this field is
+    /// used to help produce better reversed transitions.
+    pub reversing_adjusted_start_value: AnimationValue,
+
+    /// If this `Transition` has been replaced by a new one this field is
+    /// used to help produce better reversed transitions.
+    pub reversing_shortening_factor: f64,
+}
+
+impl Transition {
+    fn update_for_possibly_reversed_transition(
+        &mut self,
+        replaced_transition: &Transition,
+        delay: f64,
+        now: f64,
+    ) {
+        // If we reach here, we need to calculate a reversed transition according to
+        // https://drafts.csswg.org/css-transitions/#starting
+        //
+        //  "...if the reversing-adjusted start value of the running transition
+        //  is the same as the value of the property in the after-change style (see
+        //  the section on reversing of transitions for why these case exists),
+        //  implementations must cancel the running transition and start
+        //  a new transition..."
+        if replaced_transition.reversing_adjusted_start_value != self.property_animation.to {
+            return;
+        }
+
+        // "* reversing-adjusted start value is the end value of the running transition"
+        let replaced_animation = &replaced_transition.property_animation;
+        self.reversing_adjusted_start_value = replaced_animation.to.clone();
+
+        // "* reversing shortening factor is the absolute value, clamped to the
+        //    range [0, 1], of the sum of:
+        //    1. the output of the timing function of the old transition at the
+        //      time of the style change event, times the reversing shortening
+        //      factor of the old transition
+        //    2.  1 minus the reversing shortening factor of the old transition."
+        let transition_progress = ((now - replaced_transition.start_time) /
+            (replaced_transition.property_animation.duration))
+            .min(1.0)
+            .max(0.0);
+        let timing_function_output = replaced_animation.timing_function_output(transition_progress);
+        let old_reversing_shortening_factor = replaced_transition.reversing_shortening_factor;
+        self.reversing_shortening_factor = ((timing_function_output *
+            old_reversing_shortening_factor) +
+            (1.0 - old_reversing_shortening_factor))
+            .abs()
+            .min(1.0)
+            .max(0.0);
+
+        // "* start time is the time of the style change event plus:
+        //    1. if the matching transition delay is nonnegative, the matching
+        //       transition delay, or.
+        //    2. if the matching transition delay is negative, the product of the new
+        //       transition’s reversing shortening factor and the matching transition delay,"
+        self.start_time = if delay >= 0. {
+            now + delay
+        } else {
+            now + (self.reversing_shortening_factor * delay)
+        };
+
+        // "* end time is the start time plus the product of the matching transition
+        //    duration and the new transition’s reversing shortening factor,"
+        self.property_animation.duration *= self.reversing_shortening_factor;
+
+        // "* start value is the current value of the property in the running transition,
+        //  * end value is the value of the property in the after-change style,"
+        let procedure = Procedure::Interpolate {
+            progress: timing_function_output,
+        };
+        match replaced_animation
+            .from
+            .animate(&replaced_animation.to, procedure)
+        {
+            Ok(new_start) => self.property_animation.from = new_start,
+            Err(..) => {},
+        }
+    }
+
+    /// Whether or not this animation has ended at the provided time. This does
+    /// not take into account canceling i.e. when an animation or transition is
+    /// canceled due to changes in the style.
+    pub fn has_ended(&self, time: f64) -> bool {
+        time >= self.start_time + (self.property_animation.duration)
+    }
+
+    /// Update the given animation at a given point of progress.
+    pub fn calculate_value(&self, time: f64) -> Option<AnimationValue> {
+        let progress = (time - self.start_time) / (self.property_animation.duration);
+        if progress < 0.0 {
+            return None;
+        }
+
+        self.property_animation
+            .calculate_value(progress.min(1.0))
+            .ok()
+    }
+}
+
+/// Holds the animation state for a particular element.
+#[derive(Debug, Default, MallocSizeOf)]
+pub struct ElementAnimationSet {
+    /// The animations for this element.
+    pub animations: Vec<Animation>,
+
+    /// The transitions for this element.
+    pub transitions: Vec<Transition>,
+
+    /// Whether or not this ElementAnimationSet has had animations or transitions
+    /// which have been added, removed, or had their state changed.
+    pub dirty: bool,
+}
+
+impl ElementAnimationSet {
+    /// Cancel all animations in this `ElementAnimationSet`. This is typically called
+    /// when the element has been removed from the DOM.
+    pub fn cancel_all_animations(&mut self) {
+        self.dirty = !self.animations.is_empty();
+        for animation in self.animations.iter_mut() {
+            animation.state = AnimationState::Canceled;
+        }
+        self.cancel_active_transitions();
+    }
+
+    fn cancel_active_transitions(&mut self) {
+        for transition in self.transitions.iter_mut() {
+            if transition.state != AnimationState::Finished {
+                self.dirty = true;
+                transition.state = AnimationState::Canceled;
+            }
+        }
+    }
+
+    /// Apply all active animations.
+    pub fn apply_active_animations(
+        &self,
+        context: &SharedStyleContext,
+        style: &mut Arc<ComputedValues>,
+    ) {
+        let now = context.current_time_for_animations;
+        let mutable_style = Arc::make_mut(style);
+        if let Some(map) = self.get_value_map_for_active_animations(now) {
+            for value in map.values() {
+                value.set_in_style_for_servo(mutable_style);
+            }
+        }
+
+        if let Some(map) = self.get_value_map_for_active_transitions(now) {
+            for value in map.values() {
+                value.set_in_style_for_servo(mutable_style);
+            }
+        }
+    }
+
+    /// Clear all canceled animations and transitions from this `ElementAnimationSet`.
+    pub fn clear_canceled_animations(&mut self) {
+        self.animations
+            .retain(|animation| animation.state != AnimationState::Canceled);
+        self.transitions
+            .retain(|animation| animation.state != AnimationState::Canceled);
+    }
+
+    /// Whether this `ElementAnimationSet` is empty, which means it doesn't
+    /// hold any animations in any state.
+    pub fn is_empty(&self) -> bool {
+        self.animations.is_empty() && self.transitions.is_empty()
+    }
+
+    /// Whether or not this state needs animation ticks for its transitions
+    /// or animations.
+    pub fn needs_animation_ticks(&self) -> bool {
+        self.animations
+            .iter()
+            .any(|animation| animation.state.needs_to_be_ticked()) ||
+            self.transitions
+                .iter()
+                .any(|transition| transition.state.needs_to_be_ticked())
+    }
+
+    /// The number of running animations and transitions for this `ElementAnimationSet`.
+    pub fn running_animation_and_transition_count(&self) -> usize {
+        self.animations
+            .iter()
+            .filter(|animation| animation.state.needs_to_be_ticked())
+            .count() +
+            self.transitions
+                .iter()
+                .filter(|transition| transition.state.needs_to_be_ticked())
+                .count()
+    }
+
+    /// If this `ElementAnimationSet` has any any active animations.
+    pub fn has_active_animation(&self) -> bool {
+        self.animations
+            .iter()
+            .any(|animation| animation.state != AnimationState::Canceled)
+    }
+
+    /// If this `ElementAnimationSet` has any any active transitions.
+    pub fn has_active_transition(&self) -> bool {
+        self.transitions
+            .iter()
+            .any(|transition| transition.state != AnimationState::Canceled)
+    }
+
+    /// Update our animations given a new style, canceling or starting new animations
+    /// when appropriate.
+    pub fn update_animations_for_new_style<E>(
+        &mut self,
+        element: E,
+        context: &SharedStyleContext,
+        new_style: &Arc<ComputedValues>,
+        resolver: &mut StyleResolverForElement<E>,
+    ) where
+        E: TElement,
+    {
+        for animation in self.animations.iter_mut() {
+            if animation.is_cancelled_in_new_style(new_style) {
+                animation.state = AnimationState::Canceled;
+            }
+        }
+
+        maybe_start_animations(element, &context, &new_style, self, resolver);
+    }
+
+    /// Update our transitions given a new style, canceling or starting new animations
+    /// when appropriate.
+    pub fn update_transitions_for_new_style(
+        &mut self,
+        might_need_transitions_update: bool,
+        context: &SharedStyleContext,
+        old_style: Option<&Arc<ComputedValues>>,
+        after_change_style: &Arc<ComputedValues>,
+    ) {
+        // If this is the first style, we don't trigger any transitions and we assume
+        // there were no previously triggered transitions.
+        let mut before_change_style = match old_style {
+            Some(old_style) => Arc::clone(old_style),
+            None => return,
+        };
+
+        // If the style of this element is display:none, then cancel all active transitions.
+        if after_change_style.get_box().clone_display().is_none() {
+            self.cancel_active_transitions();
+            return;
+        }
+
+        if !might_need_transitions_update {
+            return;
+        }
+
+        // We convert old values into `before-change-style` here.
+        if self.has_active_transition() || self.has_active_animation() {
+            self.apply_active_animations(context, &mut before_change_style);
+        }
+
+        let transitioning_properties = start_transitions_if_applicable(
+            context,
+            &before_change_style,
+            after_change_style,
+            self,
+        );
+
+        // Cancel any non-finished transitions that have properties which no longer transition.
+        for transition in self.transitions.iter_mut() {
+            if transition.state == AnimationState::Finished {
+                continue;
+            }
+            if transitioning_properties.contains(transition.property_animation.property_id()) {
+                continue;
+            }
+            transition.state = AnimationState::Canceled;
+            self.dirty = true;
+        }
+    }
+
+    fn start_transition_if_applicable(
+        &mut self,
+        context: &SharedStyleContext,
+        longhand_id: LonghandId,
+        index: usize,
+        old_style: &ComputedValues,
+        new_style: &Arc<ComputedValues>,
+    ) {
+        let style = new_style.get_ui();
+        let timing_function = style.transition_timing_function_mod(index);
+        let duration = style.transition_duration_mod(index);
+        let delay = style.transition_delay_mod(index).seconds() as f64;
+        let now = context.current_time_for_animations;
+
+        // Only start a new transition if the style actually changes between
+        // the old style and the new style.
+        let property_animation = match PropertyAnimation::from_longhand(
+            longhand_id,
+            timing_function,
+            duration,
+            old_style,
+            new_style,
+        ) {
+            Some(property_animation) => property_animation,
+            None => return,
+        };
+
+        // Per [1], don't trigger a new transition if the end state for that
+        // transition is the same as that of a transition that's running or
+        // completed. We don't take into account any canceled animations.
+        // [1]: https://drafts.csswg.org/css-transitions/#starting
+        if self
+            .transitions
+            .iter()
+            .filter(|transition| transition.state != AnimationState::Canceled)
+            .any(|transition| transition.property_animation.to == property_animation.to)
+        {
+            return;
+        }
+
+        // We are going to start a new transition, but we might have to update
+        // it if we are replacing a reversed transition.
+        let reversing_adjusted_start_value = property_animation.from.clone();
+        let mut new_transition = Transition {
+            start_time: now + delay,
+            delay,
+            property_animation,
+            state: AnimationState::Pending,
+            is_new: true,
+            reversing_adjusted_start_value,
+            reversing_shortening_factor: 1.0,
+        };
+
+        if let Some(old_transition) = self
+            .transitions
+            .iter_mut()
+            .filter(|transition| transition.state == AnimationState::Running)
+            .find(|transition| transition.property_animation.property_id() == longhand_id)
+        {
+            // We always cancel any running transitions for the same property.
+            old_transition.state = AnimationState::Canceled;
+            new_transition.update_for_possibly_reversed_transition(old_transition, delay, now);
+        }
+
+        self.transitions.push(new_transition);
+        self.dirty = true;
+    }
+
+    /// Generate a `AnimationValueMap` for this `ElementAnimationSet`'s
+    /// active transitions at the given time value.
+    pub fn get_value_map_for_active_transitions(&self, now: f64) -> Option<AnimationValueMap> {
+        if !self.has_active_transition() {
+            return None;
+        }
+
+        let mut map =
+            AnimationValueMap::with_capacity_and_hasher(self.transitions.len(), Default::default());
+        for transition in &self.transitions {
+            if transition.state == AnimationState::Canceled {
+                continue;
+            }
+            let value = match transition.calculate_value(now) {
+                Some(value) => value,
+                None => continue,
+            };
+            map.insert(value.id(), value);
+        }
+
+        Some(map)
+    }
+
+    /// Generate a `AnimationValueMap` for this `ElementAnimationSet`'s
+    /// active animations at the given time value.
+    pub fn get_value_map_for_active_animations(&self, now: f64) -> Option<AnimationValueMap> {
+        if !self.has_active_animation() {
+            return None;
+        }
+
+        let mut map = Default::default();
+        for animation in &self.animations {
+            animation.get_property_declaration_at_time(now, &mut map);
+        }
+
+        Some(map)
+    }
+}
+
+#[derive(Clone, Debug, Eq, Hash, MallocSizeOf, PartialEq)]
+/// A key that is used to identify nodes in the `DocumentAnimationSet`.
+pub struct AnimationSetKey {
+    /// The node for this `AnimationSetKey`.
+    pub node: OpaqueNode,
+    /// The pseudo element for this `AnimationSetKey`. If `None` this key will
+    /// refer to the main content for its node.
+    pub pseudo_element: Option<PseudoElement>,
+}
+
+impl AnimationSetKey {
+    /// Create a new key given a node and optional pseudo element.
+    pub fn new(node: OpaqueNode, pseudo_element: Option<PseudoElement>) -> Self {
+        AnimationSetKey {
+            node,
+            pseudo_element,
+        }
+    }
+
+    /// Create a new key for the main content of this node.
+    pub fn new_for_non_pseudo(node: OpaqueNode) -> Self {
+        AnimationSetKey {
+            node,
+            pseudo_element: None,
+        }
+    }
+
+    /// Create a new key for given node and pseudo element.
+    pub fn new_for_pseudo(node: OpaqueNode, pseudo_element: PseudoElement) -> Self {
+        AnimationSetKey {
+            node,
+            pseudo_element: Some(pseudo_element),
+        }
+    }
+}
+
+#[derive(Clone, Debug, Default, MallocSizeOf)]
+/// A set of animations for a document.
+pub struct DocumentAnimationSet {
+    /// The `ElementAnimationSet`s that this set contains.
+    #[ignore_malloc_size_of = "Arc is hard"]
+    pub sets: Arc<RwLock<FxHashMap<AnimationSetKey, ElementAnimationSet>>>,
+}
+
+impl DocumentAnimationSet {
+    /// Return whether or not the provided node has active CSS animations.
+    pub fn has_active_animations(&self, key: &AnimationSetKey) -> bool {
+        self.sets
+            .read()
+            .get(key)
+            .map_or(false, |set| set.has_active_animation())
+    }
+
+    /// Return whether or not the provided node has active CSS transitions.
+    pub fn has_active_transitions(&self, key: &AnimationSetKey) -> bool {
+        self.sets
+            .read()
+            .get(key)
+            .map_or(false, |set| set.has_active_transition())
+    }
+
+    /// Return a locked PropertyDeclarationBlock with animation values for the given
+    /// key and time.
+    pub fn get_animation_declarations(
+        &self,
+        key: &AnimationSetKey,
+        time: f64,
+        shared_lock: &SharedRwLock,
+    ) -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
+        self.sets
+            .read()
+            .get(key)
+            .and_then(|set| set.get_value_map_for_active_animations(time))
+            .map(|map| {
+                let block = PropertyDeclarationBlock::from_animation_value_map(&map);
+                Arc::new(shared_lock.wrap(block))
+            })
+    }
+
+    /// Return a locked PropertyDeclarationBlock with transition values for the given
+    /// key and time.
+    pub fn get_transition_declarations(
+        &self,
+        key: &AnimationSetKey,
+        time: f64,
+        shared_lock: &SharedRwLock,
+    ) -> Option<Arc<Locked<PropertyDeclarationBlock>>> {
+        self.sets
+            .read()
+            .get(key)
+            .and_then(|set| set.get_value_map_for_active_transitions(time))
+            .map(|map| {
+                let block = PropertyDeclarationBlock::from_animation_value_map(&map);
+                Arc::new(shared_lock.wrap(block))
+            })
+    }
+
+    /// Get all the animation declarations for the given key, returning an empty
+    /// `AnimationDeclarations` if there are no animations.
+    pub fn get_all_declarations(
+        &self,
+        key: &AnimationSetKey,
+        time: f64,
+        shared_lock: &SharedRwLock,
+    ) -> AnimationDeclarations {
+        let sets = self.sets.read();
+        let set = match sets.get(key) {
+            Some(set) => set,
+            None => return Default::default(),
+        };
+
+        let animations = set.get_value_map_for_active_animations(time).map(|map| {
+            let block = PropertyDeclarationBlock::from_animation_value_map(&map);
+            Arc::new(shared_lock.wrap(block))
+        });
+        let transitions = set.get_value_map_for_active_transitions(time).map(|map| {
+            let block = PropertyDeclarationBlock::from_animation_value_map(&map);
+            Arc::new(shared_lock.wrap(block))
+        });
+        AnimationDeclarations {
+            animations,
+            transitions,
+        }
+    }
+
+    /// Cancel all animations for set at the given key.
+    pub fn cancel_all_animations_for_key(&self, key: &AnimationSetKey) {
+        if let Some(set) = self.sets.write().get_mut(key) {
+            set.cancel_all_animations();
+        }
+    }
+}
+
+/// Kick off any new transitions for this node and return all of the properties that are
+/// transitioning. This is at the end of calculating style for a single node.
+pub fn start_transitions_if_applicable(
+    context: &SharedStyleContext,
+    old_style: &ComputedValues,
+    new_style: &Arc<ComputedValues>,
+    animation_state: &mut ElementAnimationSet,
+) -> LonghandIdSet {
+    let mut properties_that_transition = LonghandIdSet::new();
+    for transition in new_style.transition_properties() {
+        let physical_property = transition.longhand_id.to_physical(new_style.writing_mode);
+        if properties_that_transition.contains(physical_property) {
+            continue;
+        }
+
+        properties_that_transition.insert(physical_property);
+        animation_state.start_transition_if_applicable(
+            context,
+            physical_property,
+            transition.index,
+            old_style,
+            new_style,
+        );
+    }
+
+    properties_that_transition
+}
+
+/// Triggers animations for a given node looking at the animation property
+/// values.
+pub fn maybe_start_animations<E>(
+    element: E,
+    context: &SharedStyleContext,
+    new_style: &Arc<ComputedValues>,
+    animation_state: &mut ElementAnimationSet,
+    resolver: &mut StyleResolverForElement<E>,
+) where
+    E: TElement,
+{
+    let style = new_style.get_ui();
+    for (i, name) in style.animation_name_iter().enumerate() {
+        let name = match name.as_atom() {
+            Some(atom) => atom,
+            None => continue,
+        };
+
+        debug!("maybe_start_animations: name={}", name);
+        let duration = style.animation_duration_mod(i).seconds() as f64;
+        if duration == 0. {
+            continue;
+        }
+
+        let keyframe_animation = match context.stylist.get_animation(name, element) {
+            Some(animation) => animation,
+            None => continue,
+        };
+
+        debug!("maybe_start_animations: animation {} found", name);
+
+        // If this animation doesn't have any keyframe, we can just continue
+        // without submitting it to the compositor, since both the first and
+        // the second keyframes would be synthetised from the computed
+        // values.
+        if keyframe_animation.steps.is_empty() {
+            continue;
+        }
+
+        // NB: This delay may be negative, meaning that the animation may be created
+        // in a state where we have advanced one or more iterations or even that the
+        // animation begins in a finished state.
+        let delay = style.animation_delay_mod(i).seconds();
+
+        let iteration_state = match style.animation_iteration_count_mod(i) {
+            AnimationIterationCount::Infinite => KeyframesIterationState::Infinite(0.0),
+            AnimationIterationCount::Number(n) => KeyframesIterationState::Finite(0.0, n.into()),
+        };
+
+        let animation_direction = style.animation_direction_mod(i);
+
+        let initial_direction = match animation_direction {
+            AnimationDirection::Normal | AnimationDirection::Alternate => {
+                AnimationDirection::Normal
+            },
+            AnimationDirection::Reverse | AnimationDirection::AlternateReverse => {
+                AnimationDirection::Reverse
+            },
+        };
+
+        let now = context.current_time_for_animations;
+        let started_at = now + delay as f64;
+        let mut starting_progress = (now - started_at) / duration;
+        let state = match style.animation_play_state_mod(i) {
+            AnimationPlayState::Paused => AnimationState::Paused(starting_progress),
+            AnimationPlayState::Running => AnimationState::Pending,
+        };
+
+        let computed_steps = ComputedKeyframe::generate_for_keyframes(
+            element,
+            &keyframe_animation,
+            context,
+            new_style,
+            style.animation_timing_function_mod(i),
+            resolver,
+        );
+
+        let mut new_animation = Animation {
+            name: name.clone(),
+            properties_changed: keyframe_animation.properties_changed,
+            computed_steps,
+            started_at,
+            duration,
+            fill_mode: style.animation_fill_mode_mod(i),
+            delay: delay as f64,
+            iteration_state,
+            state,
+            direction: animation_direction,
+            current_direction: initial_direction,
+            cascade_style: new_style.clone(),
+            is_new: true,
+        };
+
+        // If we started with a negative delay, make sure we iterate the animation if
+        // the delay moves us past the first iteration.
+        while starting_progress > 1. && !new_animation.on_last_iteration() {
+            new_animation.iterate();
+            starting_progress -= 1.;
+        }
+
+        animation_state.dirty = true;
+
+        // If the animation was already present in the list for the node, just update its state.
+        for existing_animation in animation_state.animations.iter_mut() {
+            if existing_animation.state == AnimationState::Canceled {
+                continue;
+            }
+
+            if new_animation.name == existing_animation.name {
+                existing_animation
+                    .update_from_other(&new_animation, context.current_time_for_animations);
+                return;
+            }
+        }
+
+        animation_state.animations.push(new_animation);
+    }
+}