style: C++ ComputedTimingFunction uses Rust's timing function calculation

This was made economical by having Rust's computed `easing::TimingFunction` use
a fully resolved function for `linear(...)` easing, as per draft resolution from
https://github.com/w3c/csswg-drafts/issues/7415

Differential Revision: https://phabricator.services.mozilla.com/D151295

components/style/piecewise_linear.rs

@@ -3,25 +3,64 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 //! A piecewise linear function, following CSS linear easing
+use crate::values::computed::Percentage;
+use core::slice::Iter;
 /// draft as in https://github.com/w3c/csswg-drafts/pull/6533.
 use euclid::approxeq::ApproxEq;
 use itertools::Itertools;
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ToCss};
 
 use crate::values::CSSFloat;
 
 type ValueType = CSSFloat;
 /// a single entry in a piecewise linear function.
-#[derive(Clone, Copy)]
+#[allow(missing_docs)]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToResolvedValue,
+    Serialize,
+    Deserialize,
+)]
 #[repr(C)]
-struct PiecewiseLinearFunctionEntry {
-    x: ValueType,
-    y: ValueType,
+pub struct PiecewiseLinearFunctionEntry {
+    pub x: ValueType,
+    pub y: ValueType,
+}
+
+impl ToCss for PiecewiseLinearFunctionEntry {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: fmt::Write,
+    {
+        self.y.to_css(dest)?;
+        dest.write_str(" ")?;
+        Percentage(self.x).to_css(dest)
+    }
 }
 
 /// Representation of a piecewise linear function, a series of linear functions.
-#[derive(Default)]
+#[derive(
+    Default,
+    Clone,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToResolvedValue,
+    ToCss,
+    Serialize,
+    Deserialize,
+)]
 #[repr(C)]
+#[css(comma)]
 pub struct PiecewiseLinearFunction {
+    #[css(iterable)]
     entries: crate::OwnedSlice<PiecewiseLinearFunctionEntry>,
 }
 
@@ -102,6 +141,11 @@ impl PiecewiseLinearFunction {
         }
         builder.build()
     }
+
+    #[allow(missing_docs)]
+    pub fn iter(&self) -> Iter<PiecewiseLinearFunctionEntry> {
+        self.entries.iter()
+    }
 }
 
 /// Entry of a piecewise linear function while building, where the calculation of x value can be deferred.

components/style/values/computed/easing.rs

@@ -7,31 +7,16 @@
 use euclid::approxeq::ApproxEq;
 
 use crate::bezier::Bezier;
-use crate::piecewise_linear::{PiecewiseLinearFunction, PiecewiseLinearFunctionBuildParameters};
-use crate::values::computed::{Integer, Number, Percentage};
+use crate::piecewise_linear::PiecewiseLinearFunction;
+use crate::values::computed::{Integer, Number};
 use crate::values::generics::easing::{self, BeforeFlag, StepPosition, TimingKeyword};
 
 /// A computed timing function.
-pub type ComputedTimingFunction = easing::TimingFunction<Integer, Number, Percentage>;
+pub type ComputedTimingFunction = easing::TimingFunction<Integer, Number, PiecewiseLinearFunction>;
 
 /// An alias of the computed timing function.
 pub type TimingFunction = ComputedTimingFunction;
 
-/// A computed linear easing entry.
-pub type ComputedLinearStop = easing::LinearStop<Number, Percentage>;
-
-impl ComputedLinearStop {
-    /// Convert this type to entries that can be used to build PiecewiseLinearFunction.
-    pub fn to_piecewise_linear_build_parameters(
-        x: &ComputedLinearStop,
-    ) -> PiecewiseLinearFunctionBuildParameters {
-        (
-            x.output,
-            x.input.into_rust().map(|x| x.0),
-        )
-    }
-}
-
 impl ComputedTimingFunction {
     fn calculate_step_output(
         steps: i32,
@@ -91,17 +76,7 @@ impl ComputedTimingFunction {
             TimingFunction::Steps(steps, pos) => {
                 Self::calculate_step_output(*steps, *pos, progress, before_flag)
             },
-            TimingFunction::LinearFunction(elements) => {
-                // TODO(dshin): For servo, which uses this code path, constructing the function
-                // every time the animation advances seem... expensive.
-                PiecewiseLinearFunction::from_iter(
-                    elements
-                        .iter()
-                        .map(ComputedLinearStop::to_piecewise_linear_build_parameters),
-                )
-                .at(progress as f32)
-                .into()
-            },
+            TimingFunction::LinearFunction(function) => function.at(progress as f32).into(),
             TimingFunction::Keyword(keyword) => match keyword {
                 TimingKeyword::Linear => return progress,
                 TimingKeyword::Ease => {

components/style/values/generics/easing.rs

@@ -6,31 +6,6 @@
 //! https://drafts.csswg.org/css-easing/#timing-functions
 
 use crate::parser::ParserContext;
-use crate::values::generics::Optional;
-
-/// An entry for linear easing function.
-#[derive(
-    Clone,
-    Copy,
-    Debug,
-    MallocSizeOf,
-    PartialEq,
-    SpecifiedValueInfo,
-    ToComputedValue,
-    ToCss,
-    ToResolvedValue,
-    ToShmem,
-    Serialize,
-    Deserialize,
-)]
-#[repr(C)]
-pub struct LinearStop<Number, Percentage> {
-    /// Output of the function at the given point.
-    pub output: Number,
-    /// Playback progress at which this output is given.
-    #[css(skip_if = "Optional::is_none")]
-    pub input: Optional<Percentage>,
-}
 
 /// A generic easing function.
 #[derive(
@@ -39,9 +14,7 @@ pub struct LinearStop<Number, Percentage> {
     MallocSizeOf,
     PartialEq,
     SpecifiedValueInfo,
-    ToComputedValue,
     ToCss,
-    ToResolvedValue,
     ToShmem,
     Serialize,
     Deserialize,
@@ -49,7 +22,7 @@ pub struct LinearStop<Number, Percentage> {
 #[value_info(ty = "TIMING_FUNCTION")]
 #[repr(u8, C)]
 /// cbindgen:private-default-tagged-enum-constructor=false
-pub enum TimingFunction<Integer, Number, Percentage> {
+pub enum TimingFunction<Integer, Number, LinearStops> {
     /// `linear | ease | ease-in | ease-out | ease-in-out`
     Keyword(TimingKeyword),
     /// `cubic-bezier(<number>, <number>, <number>, <number>)`
@@ -69,8 +42,8 @@ pub enum TimingFunction<Integer, Number, Percentage> {
     /// linear([<linear-stop>]#)
     /// <linear-stop> = <output> && <linear-stop-length>?
     /// <linear-stop-length> = <percentage>{1, 2}
-    #[css(comma, function = "linear")]
-    LinearFunction(#[css(iterable)] crate::OwnedSlice<LinearStop<Number, Percentage>>),
+    #[css(function = "linear")]
+    LinearFunction(LinearStops),
 }
 
 #[allow(missing_docs)]
@@ -106,7 +79,7 @@ pub enum TimingKeyword {
 #[repr(u8)]
 pub enum BeforeFlag {
     Unset,
-    Set
+    Set,
 }
 
 #[cfg(feature = "gecko")]
@@ -154,7 +127,7 @@ fn is_end(position: &StepPosition) -> bool {
     *position == StepPosition::JumpEnd || *position == StepPosition::End
 }
 
-impl<Integer, Number, Percentage> TimingFunction<Integer, Number, Percentage> {
+impl<Integer, Number, LinearStops> TimingFunction<Integer, Number, LinearStops> {
     /// `ease`
     #[inline]
     pub fn ease() -> Self {

components/style/values/resolved/mod.rs

@@ -86,6 +86,7 @@ trivial_to_resolved_value!(crate::Namespace);
 trivial_to_resolved_value!(crate::Prefix);
 trivial_to_resolved_value!(computed::LengthPercentage);
 trivial_to_resolved_value!(style_traits::values::specified::AllowedNumericType);
+trivial_to_resolved_value!(computed::TimingFunction);
 
 impl<A, B> ToResolvedValue for (A, B)
 where

components/style/values/specified/easing.rs

@@ -4,12 +4,10 @@
 
 //! Specified types for CSS Easing functions.
 use crate::parser::{Parse, ParserContext};
-use crate::values::computed::easing::ComputedLinearStop;
+use crate::piecewise_linear::{PiecewiseLinearFunction, PiecewiseLinearFunctionBuildParameters};
 use crate::values::computed::easing::TimingFunction as ComputedTimingFunction;
-use crate::values::computed::Percentage as ComputedPercentage;
-use crate::values::generics::easing::{
-    LinearStop as GenericLinearStop, TimingFunction as GenericTimingFunction,
-};
+use crate::values::computed::{Context, ToComputedValue};
+use crate::values::generics::easing::TimingFunction as GenericTimingFunction;
 use crate::values::generics::easing::{StepPosition, TimingKeyword};
 use crate::values::specified::{Integer, Number, Percentage};
 use cssparser::{Delimiter, Parser, Token};
@@ -17,10 +15,32 @@ use selectors::parser::SelectorParseErrorKind;
 use std::iter::FromIterator;
 use style_traits::{ParseError, StyleParseErrorKind};
 
-/// A specified timing function.
-pub type TimingFunction = GenericTimingFunction<Integer, Number, Percentage>;
+/// An entry for linear easing function.
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
+pub struct LinearStop {
+    /// Output of the function at the given point.
+    pub output: Number,
+    /// Playback progress at which this output is given.
+    #[css(skip_if = "Option::is_none")]
+    pub input: Option<Percentage>,
+}
 
-type LinearStop = GenericLinearStop<Number, Percentage>;
+/// A list of specified linear stops.
+#[derive(Clone, Default, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
+#[css(comma)]
+pub struct LinearStops {
+    #[css(iterable)]
+    entries: crate::OwnedSlice<LinearStop>,
+}
+
+impl LinearStops {
+    fn new(list: crate::OwnedSlice<LinearStop>) -> Self {
+        LinearStops { entries: list }
+    }
+}
+
+/// A specified timing function.
+pub type TimingFunction = GenericTimingFunction<Integer, Number, LinearStops>;
 
 #[cfg(feature = "gecko")]
 fn linear_timing_function_enabled() -> bool {
@@ -115,7 +135,7 @@ impl TimingFunction {
             return Err(input.new_custom_error(StyleParseErrorKind::ExperimentalProperty));
         }
         if input.is_exhausted() {
-            return Ok(GenericTimingFunction::LinearFunction(crate::OwnedSlice::default()))
+            return Ok(GenericTimingFunction::LinearFunction(LinearStops::default()));
         }
         let mut result = vec![];
         loop {
@@ -145,7 +165,18 @@ impl TimingFunction {
             }
         }
 
-        Ok(GenericTimingFunction::LinearFunction(crate::OwnedSlice::from(result)))
+        Ok(GenericTimingFunction::LinearFunction(LinearStops::new(
+            crate::OwnedSlice::from(result),
+        )))
+    }
+}
+
+impl LinearStop {
+    /// Convert this type to entries that can be used to build PiecewiseLinearFunction.
+    pub fn to_piecewise_linear_build_parameters(
+        x: &LinearStop,
+    ) -> PiecewiseLinearFunctionBuildParameters {
+        (x.output.get(), x.input.map(|x| x.get()))
     }
 }
 
@@ -169,15 +200,40 @@ impl TimingFunction {
             },
             GenericTimingFunction::Keyword(keyword) => GenericTimingFunction::Keyword(*keyword),
             GenericTimingFunction::LinearFunction(steps) => {
-                let iter = steps.iter().map(|e| ComputedLinearStop {
-                    output: e.output.get(),
-                    input: e
-                        .input
-                        .into_rust()
-                        .map(|x| ComputedPercentage(x.get()))
-                        .into(),
-                });
-                GenericTimingFunction::LinearFunction(crate::OwnedSlice::from_iter(iter))
+                GenericTimingFunction::LinearFunction(PiecewiseLinearFunction::from_iter(
+                    steps
+                        .entries
+                        .iter()
+                        .map(|e| LinearStop::to_piecewise_linear_build_parameters(e)),
+                ))
+            },
+        }
+    }
+}
+
+impl ToComputedValue for TimingFunction {
+    type ComputedValue = ComputedTimingFunction;
+    fn to_computed_value(&self, _: &Context) -> Self::ComputedValue {
+        self.to_computed_value_without_context()
+    }
+
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        match &computed {
+            ComputedTimingFunction::Steps(steps, pos) => Self::Steps(Integer::new(*steps), *pos),
+            ComputedTimingFunction::CubicBezier { x1, y1, x2, y2 } => Self::CubicBezier {
+                x1: Number::new(*x1),
+                y1: Number::new(*y1),
+                x2: Number::new(*x2),
+                y2: Number::new(*y2),
+            },
+            ComputedTimingFunction::Keyword(keyword) => GenericTimingFunction::Keyword(*keyword),
+            ComputedTimingFunction::LinearFunction(function) => {
+                GenericTimingFunction::LinearFunction(LinearStops {
+                    entries: crate::OwnedSlice::from_iter(function.iter().map(|e| LinearStop {
+                        output: Number::new(e.y),
+                        input: Some(Percentage::new(e.x)).into(),
+                    })),
+                })
             },
         }
     }