Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

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

1 files changed, 293 insertions, 0 deletions

diff --git a/servo/components/style/piecewise_linear.rs b/servo/components/style/piecewise_linear.rs
new file mode 100644
index 0000000000..84ccb7061c
--- /dev/null
+++ b/servo/components/style/piecewise_linear.rs
@@ -0,0 +1,293 @@
+/* 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/. */
+
+//! 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.
+#[allow(missing_docs)]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToResolvedValue,
+    Serialize,
+    Deserialize,
+)]
+#[repr(C)]
+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_char(' ')?;
+        Percentage(self.x).to_css(dest)
+    }
+}
+
+/// Representation of a piecewise linear function, a series of linear functions.
+#[derive(
+    Default,
+    Clone,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToResolvedValue,
+    ToCss,
+    Serialize,
+    Deserialize,
+)]
+#[repr(C)]
+#[css(comma)]
+pub struct PiecewiseLinearFunction {
+    #[css(iterable)]
+    entries: crate::OwnedSlice<PiecewiseLinearFunctionEntry>,
+}
+
+/// Parameters to define one linear stop.
+pub type PiecewiseLinearFunctionBuildParameters = (CSSFloat, Option<CSSFloat>);
+
+impl PiecewiseLinearFunction {
+    /// Interpolate y value given x and two points. The linear function will be rooted at the asymptote.
+    fn interpolate(
+        x: ValueType,
+        prev: PiecewiseLinearFunctionEntry,
+        next: PiecewiseLinearFunctionEntry,
+        asymptote: &PiecewiseLinearFunctionEntry,
+    ) -> ValueType {
+        // Short circuit if the x is on prev or next.
+        // `next` point is preferred as per spec.
+        if x.approx_eq(&next.x) {
+            return next.y;
+        }
+        if x.approx_eq(&prev.x) {
+            return prev.y;
+        }
+        // Avoid division by zero.
+        if prev.x.approx_eq(&next.x) {
+            return next.y;
+        }
+        let slope = (next.y - prev.y) / (next.x - prev.x);
+        return slope * (x - asymptote.x) + asymptote.y;
+    }
+
+    /// Get the y value of the piecewise linear function given the x value, as per
+    /// https://drafts.csswg.org/css-easing-2/#linear-easing-function-output
+    pub fn at(&self, x: ValueType) -> ValueType {
+        if !x.is_finite() {
+            return if x > 0.0 { 1.0 } else { 0.0 };
+        }
+        if self.entries.is_empty() {
+            // Implied y = x, as per spec.
+            return x;
+        }
+        if self.entries.len() == 1 {
+            // Implied y = <constant>, as per spec.
+            return self.entries[0].y;
+        }
+        // Spec dictates the valid input domain is [0, 1]. Outside of this range, the output
+        // should be calculated as if the slopes at start and end extend to infinity. However, if the
+        // start/end have two points of the same position, the line should extend along the x-axis.
+        // The function doesn't have to cover the input domain, in which case the extension logic
+        // applies even if the input falls in the input domain.
+        // Also, we're guaranteed to have at least two elements at this point.
+        if x < self.entries[0].x {
+            return Self::interpolate(x, self.entries[0], self.entries[1], &self.entries[0]);
+        }
+        let mut rev_iter = self.entries.iter().rev();
+        let last = rev_iter.next().unwrap();
+        if x >= last.x {
+            let second_last = rev_iter.next().unwrap();
+            return Self::interpolate(x, *second_last, *last, last);
+        }
+
+        // Now we know the input sits within the domain explicitly defined by our function.
+        for (point_b, point_a) in self.entries.iter().rev().tuple_windows() {
+            // Need to let point A be the _last_ point where its x is less than the input x,
+            // hence the reverse traversal.
+            if x < point_a.x {
+                continue;
+            }
+            return Self::interpolate(x, *point_a, *point_b, point_a);
+        }
+        unreachable!("Input is supposed to be within the entries' min & max!");
+    }
+
+    /// Create the piecewise linear function from an iterator that generates the parameter tuple.
+    pub fn from_iter<Iter>(iter: Iter) -> Self
+    where
+        Iter: Iterator<Item = PiecewiseLinearFunctionBuildParameters> + ExactSizeIterator,
+    {
+        let mut builder = PiecewiseLinearFunctionBuilder::with_capacity(iter.len());
+        for (y, x_start) in iter {
+            builder = builder.push(y, x_start);
+        }
+        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.
+#[derive(Clone, Copy)]
+struct BuildEntry {
+    x: Option<ValueType>,
+    y: ValueType,
+}
+
+/// Builder object to generate a linear function.
+#[derive(Default)]
+pub struct PiecewiseLinearFunctionBuilder {
+    largest_x: Option<ValueType>,
+    smallest_x: Option<ValueType>,
+    entries: Vec<BuildEntry>,
+}
+
+impl PiecewiseLinearFunctionBuilder {
+    #[allow(missing_docs)]
+    pub fn new() -> Self {
+        PiecewiseLinearFunctionBuilder::default()
+    }
+
+    /// Create a builder for a known amount of linear stop entries.
+    pub fn with_capacity(len: usize) -> Self {
+        PiecewiseLinearFunctionBuilder {
+            largest_x: None,
+            smallest_x: None,
+            entries: Vec::with_capacity(len),
+        }
+    }
+
+    fn create_entry(&mut self, y: ValueType, x: Option<ValueType>) {
+        let x = match x {
+            Some(x) if x.is_finite() => x,
+            _ if self.entries.is_empty() => 0.0, // First x is 0 if not specified (Or not finite)
+            _ => {
+                self.entries.push(BuildEntry { x: None, y });
+                return;
+            },
+        };
+        // Specified x value cannot regress, as per spec.
+        let x = match self.largest_x {
+            Some(largest_x) => x.max(largest_x),
+            None => x,
+        };
+        self.largest_x = Some(x);
+        // Whatever we see the earliest is the smallest value.
+        if self.smallest_x.is_none() {
+            self.smallest_x = Some(x);
+        }
+        self.entries.push(BuildEntry { x: Some(x), y });
+    }
+
+    /// Add a new entry into the piecewise linear function with specified y value.
+    /// If the start x value is given, that is where the x value will be. Otherwise,
+    /// the x value is calculated later. If the end x value is specified, a flat segment
+    /// is generated. If start x value is not specified but end x is, it is treated as
+    /// start x.
+    pub fn push(mut self, y: CSSFloat, x_start: Option<CSSFloat>) -> Self {
+        self.create_entry(y, x_start);
+        self
+    }
+
+    /// Finish building the piecewise linear function by resolving all undefined x values,
+    /// then return the result.
+    pub fn build(mut self) -> PiecewiseLinearFunction {
+        if self.entries.is_empty() {
+            return PiecewiseLinearFunction::default();
+        }
+        if self.entries.len() == 1 {
+            // Don't bother resolving anything.
+            return PiecewiseLinearFunction {
+                entries: crate::OwnedSlice::from_slice(&[PiecewiseLinearFunctionEntry {
+                    x: 0.,
+                    y: self.entries[0].y,
+                }]),
+            };
+        }
+        // Guaranteed at least two elements.
+        // Start element's x value should've been assigned when the first value was pushed.
+        debug_assert!(
+            self.entries[0].x.is_some(),
+            "Expected an entry with x defined!"
+        );
+        // Spec asserts that if the last entry does not have an x value, it is assigned the largest seen x value.
+        self.entries
+            .last_mut()
+            .unwrap()
+            .x
+            .get_or_insert(self.largest_x.filter(|x| x > &1.0).unwrap_or(1.0));
+        // Now we have at least two elements with x values, with start & end x values guaranteed.
+
+        let mut result = Vec::with_capacity(self.entries.len());
+        result.push(PiecewiseLinearFunctionEntry {
+            x: self.entries[0].x.unwrap(),
+            y: self.entries[0].y,
+        });
+        for (i, e) in self.entries.iter().enumerate().skip(1) {
+            if e.x.is_none() {
+                // Need to calculate x values by first finding an entry with the first
+                // defined x value (Guaranteed to exist as the list end has it defined).
+                continue;
+            }
+            // x is defined for this element.
+            let divisor = i - result.len() + 1;
+            // Any element(s) with undefined x to assign?
+            if divisor != 1 {
+                // Have at least one element in result at all times.
+                let start_x = result.last().unwrap().x;
+                let increment = (e.x.unwrap() - start_x) / divisor as ValueType;
+                // Grab every element with undefined x to this point, which starts at the end of the result
+                // array, and ending right before the current index. Then, assigned the evenly divided
+                // x values.
+                result.extend(
+                    self.entries[result.len()..i]
+                        .iter()
+                        .enumerate()
+                        .map(|(j, e)| {
+                            debug_assert!(e.x.is_none(), "Expected an entry with x undefined!");
+                            PiecewiseLinearFunctionEntry {
+                                x: increment * (j + 1) as ValueType + start_x,
+                                y: e.y,
+                            }
+                        }),
+                );
+            }
+            result.push(PiecewiseLinearFunctionEntry {
+                x: e.x.unwrap(),
+                y: e.y,
+            });
+        }
+        debug_assert_eq!(
+            result.len(),
+            self.entries.len(),
+            "Should've mapped one-to-one!"
+        );
+        PiecewiseLinearFunction {
+            entries: result.into(),
+        }
+    }
+}