servo/components/style/values/generics/transform.rs
author Emilio Cobos Álvarez <emilio@crisal.io>
Tue, 16 Jul 2019 23:11:42 +0000
changeset 483035 05c5e4d30587aeab3f566e07edda1a3e6d22c41e
parent 481620 fa37846c0dc35398d37db6ab832fdd930446920a
permissions -rw-r--r--
Bug 1561794 - Do not to crop display text of themed comboboxes due to padding. r=dbaron This is a potential fix that I thought it was worth doing rather than implementing Blink's platform-dependent silliness. This ensures that the display frame always has enough space to display itself. Note that it may still get clipped, if there's no room for both the display frame and the button. Differential Revision: https://phabricator.services.mozilla.com/D37922

/* 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/. */

//! Generic types for CSS values that are related to transformations.

use crate::values::computed::length::Length as ComputedLength;
use crate::values::computed::length::LengthPercentage as ComputedLengthPercentage;
use crate::values::specified::angle::Angle as SpecifiedAngle;
use crate::values::specified::length::Length as SpecifiedLength;
use crate::values::specified::length::LengthPercentage as SpecifiedLengthPercentage;
use crate::values::{computed, CSSFloat};
use crate::Zero;
use app_units::Au;
use euclid::{self, Rect, Transform3D};
use std::fmt::{self, Write};
use style_traits::{CssWriter, ToCss};

/// A generic 2D transformation matrix.
#[allow(missing_docs)]
#[derive(
    Clone,
    Copy,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[css(comma, function = "matrix")]
#[repr(C)]
pub struct GenericMatrix<T> {
    pub a: T,
    pub b: T,
    pub c: T,
    pub d: T,
    pub e: T,
    pub f: T,
}

pub use self::GenericMatrix as Matrix;

#[allow(missing_docs)]
#[cfg_attr(rustfmt, rustfmt_skip)]
#[css(comma, function = "matrix3d")]
#[derive(
    Clone,
    Copy,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
pub struct GenericMatrix3D<T> {
    pub m11: T, pub m12: T, pub m13: T, pub m14: T,
    pub m21: T, pub m22: T, pub m23: T, pub m24: T,
    pub m31: T, pub m32: T, pub m33: T, pub m34: T,
    pub m41: T, pub m42: T, pub m43: T, pub m44: T,
}

pub use self::GenericMatrix3D as Matrix3D;

#[cfg_attr(rustfmt, rustfmt_skip)]
impl<T: Into<f64>> From<Matrix<T>> for Transform3D<f64> {
    #[inline]
    fn from(m: Matrix<T>) -> Self {
        Transform3D::row_major(
            m.a.into(), m.b.into(), 0.0, 0.0,
            m.c.into(), m.d.into(), 0.0, 0.0,
            0.0,        0.0,        1.0, 0.0,
            m.e.into(), m.f.into(), 0.0, 1.0,
        )
    }
}

#[cfg_attr(rustfmt, rustfmt_skip)]
impl<T: Into<f64>> From<Matrix3D<T>> for Transform3D<f64> {
    #[inline]
    fn from(m: Matrix3D<T>) -> Self {
        Transform3D::row_major(
            m.m11.into(), m.m12.into(), m.m13.into(), m.m14.into(),
            m.m21.into(), m.m22.into(), m.m23.into(), m.m24.into(),
            m.m31.into(), m.m32.into(), m.m33.into(), m.m34.into(),
            m.m41.into(), m.m42.into(), m.m43.into(), m.m44.into(),
        )
    }
}

/// A generic transform origin.
#[derive(
    Animate,
    Clone,
    ComputeSquaredDistance,
    Copy,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToAnimatedZero,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
pub struct GenericTransformOrigin<H, V, Depth> {
    /// The horizontal origin.
    pub horizontal: H,
    /// The vertical origin.
    pub vertical: V,
    /// The depth.
    pub depth: Depth,
}

pub use self::GenericTransformOrigin as TransformOrigin;

impl<H, V, D> TransformOrigin<H, V, D> {
    /// Returns a new transform origin.
    pub fn new(horizontal: H, vertical: V, depth: D) -> Self {
        Self {
            horizontal,
            vertical,
            depth,
        }
    }
}

fn is_same<N: PartialEq>(x: &N, y: &N) -> bool {
    x == y
}

#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C, u8)]
/// A single operation in the list of a `transform` value
/// cbindgen:derive-tagged-enum-copy-constructor=true
pub enum GenericTransformOperation<Angle, Number, Length, Integer, LengthPercentage>
where
    Angle: Zero,
    LengthPercentage: Zero,
    Number: PartialEq,
{
    /// Represents a 2D 2x3 matrix.
    Matrix(GenericMatrix<Number>),
    /// Represents a 3D 4x4 matrix.
    Matrix3D(GenericMatrix3D<Number>),
    /// A 2D skew.
    ///
    /// If the second angle is not provided it is assumed zero.
    ///
    /// Syntax can be skew(angle) or skew(angle, angle)
    #[css(comma, function)]
    Skew(Angle, #[css(skip_if = "Zero::is_zero")] Angle),
    /// skewX(angle)
    #[css(function = "skewX")]
    SkewX(Angle),
    /// skewY(angle)
    #[css(function = "skewY")]
    SkewY(Angle),
    /// translate(x, y) or translate(x)
    #[css(comma, function)]
    Translate(
        LengthPercentage,
        #[css(skip_if = "Zero::is_zero")] LengthPercentage,
    ),
    /// translateX(x)
    #[css(function = "translateX")]
    TranslateX(LengthPercentage),
    /// translateY(y)
    #[css(function = "translateY")]
    TranslateY(LengthPercentage),
    /// translateZ(z)
    #[css(function = "translateZ")]
    TranslateZ(Length),
    /// translate3d(x, y, z)
    #[css(comma, function = "translate3d")]
    Translate3D(LengthPercentage, LengthPercentage, Length),
    /// A 2D scaling factor.
    ///
    /// Syntax can be scale(factor) or scale(factor, factor)
    #[css(comma, function)]
    Scale(Number, #[css(contextual_skip_if = "is_same")] Number),
    /// scaleX(factor)
    #[css(function = "scaleX")]
    ScaleX(Number),
    /// scaleY(factor)
    #[css(function = "scaleY")]
    ScaleY(Number),
    /// scaleZ(factor)
    #[css(function = "scaleZ")]
    ScaleZ(Number),
    /// scale3D(factorX, factorY, factorZ)
    #[css(comma, function = "scale3d")]
    Scale3D(Number, Number, Number),
    /// Describes a 2D Rotation.
    ///
    /// In a 3D scene `rotate(angle)` is equivalent to `rotateZ(angle)`.
    #[css(function)]
    Rotate(Angle),
    /// Rotation in 3D space around the x-axis.
    #[css(function = "rotateX")]
    RotateX(Angle),
    /// Rotation in 3D space around the y-axis.
    #[css(function = "rotateY")]
    RotateY(Angle),
    /// Rotation in 3D space around the z-axis.
    #[css(function = "rotateZ")]
    RotateZ(Angle),
    /// Rotation in 3D space.
    ///
    /// Generalization of rotateX, rotateY and rotateZ.
    #[css(comma, function = "rotate3d")]
    Rotate3D(Number, Number, Number, Angle),
    /// Specifies a perspective projection matrix.
    ///
    /// Part of CSS Transform Module Level 2 and defined at
    /// [ยง 13.1. 3D Transform Function](https://drafts.csswg.org/css-transforms-2/#funcdef-perspective).
    ///
    /// The value must be greater than or equal to zero.
    #[css(function)]
    Perspective(Length),
    /// A intermediate type for interpolation of mismatched transform lists.
    #[allow(missing_docs)]
    #[css(comma, function = "interpolatematrix")]
    InterpolateMatrix {
        from_list: GenericTransform<
            GenericTransformOperation<Angle, Number, Length, Integer, LengthPercentage>,
        >,
        to_list: GenericTransform<
            GenericTransformOperation<Angle, Number, Length, Integer, LengthPercentage>,
        >,
        progress: computed::Percentage,
    },
    /// A intermediate type for accumulation of mismatched transform lists.
    #[allow(missing_docs)]
    #[css(comma, function = "accumulatematrix")]
    AccumulateMatrix {
        from_list: GenericTransform<
            GenericTransformOperation<Angle, Number, Length, Integer, LengthPercentage>,
        >,
        to_list: GenericTransform<
            GenericTransformOperation<Angle, Number, Length, Integer, LengthPercentage>,
        >,
        count: Integer,
    },
}

pub use self::GenericTransformOperation as TransformOperation;

#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C)]
/// A value of the `transform` property
pub struct GenericTransform<T>(#[css(if_empty = "none", iterable)] pub crate::OwnedSlice<T>);

pub use self::GenericTransform as Transform;

impl<Angle, Number, Length, Integer, LengthPercentage>
    TransformOperation<Angle, Number, Length, Integer, LengthPercentage>
where
    Angle: Zero,
    LengthPercentage: Zero,
    Number: PartialEq,
{
    /// Check if it is any rotate function.
    pub fn is_rotate(&self) -> bool {
        use self::TransformOperation::*;
        matches!(
            *self,
            Rotate(..) | Rotate3D(..) | RotateX(..) | RotateY(..) | RotateZ(..)
        )
    }

    /// Check if it is any translate function
    pub fn is_translate(&self) -> bool {
        use self::TransformOperation::*;
        match *self {
            Translate(..) | Translate3D(..) | TranslateX(..) | TranslateY(..) | TranslateZ(..) => {
                true
            },
            _ => false,
        }
    }

    /// Check if it is any scale function
    pub fn is_scale(&self) -> bool {
        use self::TransformOperation::*;
        match *self {
            Scale(..) | Scale3D(..) | ScaleX(..) | ScaleY(..) | ScaleZ(..) => true,
            _ => false,
        }
    }
}

/// Convert a length type into the absolute lengths.
pub trait ToAbsoluteLength {
    /// Returns the absolute length as pixel value.
    fn to_pixel_length(&self, containing_len: Option<Au>) -> Result<CSSFloat, ()>;
}

impl ToAbsoluteLength for SpecifiedLength {
    // This returns Err(()) if there is any relative length or percentage. We use this when
    // parsing a transform list of DOMMatrix because we want to return a DOM Exception
    // if there is relative length.
    #[inline]
    fn to_pixel_length(&self, _containing_len: Option<Au>) -> Result<CSSFloat, ()> {
        match *self {
            SpecifiedLength::NoCalc(len) => len.to_computed_pixel_length_without_context(),
            SpecifiedLength::Calc(ref calc) => calc.to_computed_pixel_length_without_context(),
        }
    }
}

impl ToAbsoluteLength for SpecifiedLengthPercentage {
    // This returns Err(()) if there is any relative length or percentage. We use this when
    // parsing a transform list of DOMMatrix because we want to return a DOM Exception
    // if there is relative length.
    #[inline]
    fn to_pixel_length(&self, _containing_len: Option<Au>) -> Result<CSSFloat, ()> {
        use self::SpecifiedLengthPercentage::*;
        match *self {
            Length(len) => len.to_computed_pixel_length_without_context(),
            Calc(ref calc) => calc.to_computed_pixel_length_without_context(),
            _ => Err(()),
        }
    }
}

impl ToAbsoluteLength for ComputedLength {
    #[inline]
    fn to_pixel_length(&self, _containing_len: Option<Au>) -> Result<CSSFloat, ()> {
        Ok(self.px())
    }
}

impl ToAbsoluteLength for ComputedLengthPercentage {
    #[inline]
    fn to_pixel_length(&self, containing_len: Option<Au>) -> Result<CSSFloat, ()> {
        match containing_len {
            Some(relative_len) => Ok(self.to_pixel_length(relative_len).px()),
            // If we don't have reference box, we cannot resolve the used value,
            // so only retrieve the length part. This will be used for computing
            // distance without any layout info.
            //
            // FIXME(emilio): This looks wrong.
            None => Ok(self.length_component().px()),
        }
    }
}

/// Support the conversion to a 3d matrix.
pub trait ToMatrix {
    /// Check if it is a 3d transform function.
    fn is_3d(&self) -> bool;

    /// Return the equivalent 3d matrix.
    fn to_3d_matrix(&self, reference_box: Option<&Rect<Au>>) -> Result<Transform3D<f64>, ()>;
}

/// A little helper to deal with both specified and computed angles.
pub trait ToRadians {
    /// Return the radians value as a 64-bit floating point value.
    fn radians64(&self) -> f64;
}

impl ToRadians for computed::angle::Angle {
    #[inline]
    fn radians64(&self) -> f64 {
        computed::angle::Angle::radians64(self)
    }
}

impl ToRadians for SpecifiedAngle {
    #[inline]
    fn radians64(&self) -> f64 {
        computed::angle::Angle::from_degrees(self.degrees()).radians64()
    }
}

impl<Angle, Number, Length, Integer, LoP> ToMatrix
    for TransformOperation<Angle, Number, Length, Integer, LoP>
where
    Angle: Zero + ToRadians + Copy,
    Number: PartialEq + Copy + Into<f32> + Into<f64>,
    Length: ToAbsoluteLength,
    LoP: Zero + ToAbsoluteLength,
{
    #[inline]
    fn is_3d(&self) -> bool {
        use self::TransformOperation::*;
        match *self {
            Translate3D(..) | TranslateZ(..) | Rotate3D(..) | RotateX(..) | RotateY(..) |
            RotateZ(..) | Scale3D(..) | ScaleZ(..) | Perspective(..) | Matrix3D(..) => true,
            _ => false,
        }
    }

    /// If |reference_box| is None, we will drop the percent part from translate because
    /// we cannot resolve it without the layout info, for computed TransformOperation.
    /// However, for specified TransformOperation, we will return Err(()) if there is any relative
    /// lengths because the only caller, DOMMatrix, doesn't accept relative lengths.
    #[inline]
    fn to_3d_matrix(&self, reference_box: Option<&Rect<Au>>) -> Result<Transform3D<f64>, ()> {
        use self::TransformOperation::*;
        use std::f64;

        const TWO_PI: f64 = 2.0f64 * f64::consts::PI;
        let reference_width = reference_box.map(|v| v.size.width);
        let reference_height = reference_box.map(|v| v.size.height);
        let matrix = match *self {
            Rotate3D(ax, ay, az, theta) => {
                let theta = TWO_PI - theta.radians64();
                let (ax, ay, az, theta) =
                    get_normalized_vector_and_angle(ax.into(), ay.into(), az.into(), theta);
                Transform3D::create_rotation(
                    ax as f64,
                    ay as f64,
                    az as f64,
                    euclid::Angle::radians(theta),
                )
            },
            RotateX(theta) => {
                let theta = euclid::Angle::radians(TWO_PI - theta.radians64());
                Transform3D::create_rotation(1., 0., 0., theta)
            },
            RotateY(theta) => {
                let theta = euclid::Angle::radians(TWO_PI - theta.radians64());
                Transform3D::create_rotation(0., 1., 0., theta)
            },
            RotateZ(theta) | Rotate(theta) => {
                let theta = euclid::Angle::radians(TWO_PI - theta.radians64());
                Transform3D::create_rotation(0., 0., 1., theta)
            },
            Perspective(ref d) => {
                let m = create_perspective_matrix(d.to_pixel_length(None)?);
                m.cast()
            },
            Scale3D(sx, sy, sz) => Transform3D::create_scale(sx.into(), sy.into(), sz.into()),
            Scale(sx, sy) => Transform3D::create_scale(sx.into(), sy.into(), 1.),
            ScaleX(s) => Transform3D::create_scale(s.into(), 1., 1.),
            ScaleY(s) => Transform3D::create_scale(1., s.into(), 1.),
            ScaleZ(s) => Transform3D::create_scale(1., 1., s.into()),
            Translate3D(ref tx, ref ty, ref tz) => {
                let tx = tx.to_pixel_length(reference_width)? as f64;
                let ty = ty.to_pixel_length(reference_height)? as f64;
                Transform3D::create_translation(tx, ty, tz.to_pixel_length(None)? as f64)
            },
            Translate(ref tx, ref ty) => {
                let tx = tx.to_pixel_length(reference_width)? as f64;
                let ty = ty.to_pixel_length(reference_height)? as f64;
                Transform3D::create_translation(tx, ty, 0.)
            },
            TranslateX(ref t) => {
                let t = t.to_pixel_length(reference_width)? as f64;
                Transform3D::create_translation(t, 0., 0.)
            },
            TranslateY(ref t) => {
                let t = t.to_pixel_length(reference_height)? as f64;
                Transform3D::create_translation(0., t, 0.)
            },
            TranslateZ(ref z) => {
                Transform3D::create_translation(0., 0., z.to_pixel_length(None)? as f64)
            },
            Skew(theta_x, theta_y) => Transform3D::create_skew(
                euclid::Angle::radians(theta_x.radians64()),
                euclid::Angle::radians(theta_y.radians64()),
            ),
            SkewX(theta) => Transform3D::create_skew(
                euclid::Angle::radians(theta.radians64()),
                euclid::Angle::radians(0.),
            ),
            SkewY(theta) => Transform3D::create_skew(
                euclid::Angle::radians(0.),
                euclid::Angle::radians(theta.radians64()),
            ),
            Matrix3D(m) => m.into(),
            Matrix(m) => m.into(),
            InterpolateMatrix { .. } | AccumulateMatrix { .. } => {
                // TODO: Convert InterpolateMatrix/AccumulateMatrix into a valid Transform3D by
                // the reference box and do interpolation on these two Transform3D matrices.
                // Both Gecko and Servo don't support this for computing distance, and Servo
                // doesn't support animations on InterpolateMatrix/AccumulateMatrix, so
                // return an identity matrix.
                // Note: DOMMatrix doesn't go into this arm.
                Transform3D::identity()
            },
        };
        Ok(matrix)
    }
}

impl<T> Transform<T> {
    /// `none`
    pub fn none() -> Self {
        Transform(Default::default())
    }
}

impl<T: ToMatrix> Transform<T> {
    /// Return the equivalent 3d matrix of this transform list.
    /// We return a pair: the first one is the transform matrix, and the second one
    /// indicates if there is any 3d transform function in this transform list.
    #[cfg_attr(rustfmt, rustfmt_skip)]
    pub fn to_transform_3d_matrix(
        &self,
        reference_box: Option<&Rect<Au>>
    ) -> Result<(Transform3D<CSSFloat>, bool), ()> {
        let cast_3d_transform = |m: Transform3D<f64>| -> Transform3D<CSSFloat> {
            use std::{f32, f64};
            let cast = |v: f64| { v.min(f32::MAX as f64).max(f32::MIN as f64) as f32 };
            Transform3D::row_major(
                cast(m.m11), cast(m.m12), cast(m.m13), cast(m.m14),
                cast(m.m21), cast(m.m22), cast(m.m23), cast(m.m24),
                cast(m.m31), cast(m.m32), cast(m.m33), cast(m.m34),
                cast(m.m41), cast(m.m42), cast(m.m43), cast(m.m44),
            )
        };

        let (m, is_3d) = self.to_transform_3d_matrix_f64(reference_box)?;
        Ok((cast_3d_transform(m), is_3d))
    }

    /// Same as Transform::to_transform_3d_matrix but a f64 version.
    pub fn to_transform_3d_matrix_f64(
        &self,
        reference_box: Option<&Rect<Au>>,
    ) -> Result<(Transform3D<f64>, bool), ()> {
        // We intentionally use Transform3D<f64> during computation to avoid error propagation
        // because using f32 to compute triangle functions (e.g. in create_rotation()) is not
        // accurate enough. In Gecko, we also use "double" to compute the triangle functions.
        // Therefore, let's use Transform3D<f64> during matrix computation and cast it into f32
        // in the end.
        let mut transform = Transform3D::<f64>::identity();
        let mut contain_3d = false;

        for operation in &*self.0 {
            let matrix = operation.to_3d_matrix(reference_box)?;
            contain_3d |= operation.is_3d();
            transform = transform.pre_mul(&matrix);
        }

        Ok((transform, contain_3d))
    }
}

/// Return the transform matrix from a perspective length.
#[inline]
pub fn create_perspective_matrix(d: CSSFloat) -> Transform3D<CSSFloat> {
    // TODO(gw): The transforms spec says that perspective length must
    // be positive. However, there is some confusion between the spec
    // and browser implementations as to handling the case of 0 for the
    // perspective value. Until the spec bug is resolved, at least ensure
    // that a provided perspective value of <= 0.0 doesn't cause panics
    // and behaves as it does in other browsers.
    // See https://lists.w3.org/Archives/Public/www-style/2016Jan/0020.html for more details.
    if d <= 0.0 {
        Transform3D::identity()
    } else {
        Transform3D::create_perspective(d)
    }
}

/// Return the normalized direction vector and its angle for Rotate3D.
pub fn get_normalized_vector_and_angle<T: Zero>(
    x: CSSFloat,
    y: CSSFloat,
    z: CSSFloat,
    angle: T,
) -> (CSSFloat, CSSFloat, CSSFloat, T) {
    use crate::values::computed::transform::DirectionVector;
    use euclid::approxeq::ApproxEq;
    let vector = DirectionVector::new(x, y, z);
    if vector.square_length().approx_eq(&f32::zero()) {
        // https://www.w3.org/TR/css-transforms-1/#funcdef-rotate3d
        // A direction vector that cannot be normalized, such as [0, 0, 0], will cause the
        // rotation to not be applied, so we use identity matrix (i.e. rotate3d(0, 0, 1, 0)).
        (0., 0., 1., T::zero())
    } else {
        let vector = vector.robust_normalize();
        (vector.x, vector.y, vector.z, angle)
    }
}

#[derive(
    Clone,
    Copy,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToAnimatedZero,
    ToComputedValue,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C, u8)]
/// A value of the `Rotate` property
///
/// <https://drafts.csswg.org/css-transforms-2/#individual-transforms>
pub enum GenericRotate<Number, Angle> {
    /// 'none'
    None,
    /// '<angle>'
    Rotate(Angle),
    /// '<number>{3} <angle>'
    Rotate3D(Number, Number, Number, Angle),
}

pub use self::GenericRotate as Rotate;

/// A trait to check if the current 3D vector is parallel to the DirectionVector.
/// This is especially for serialization on Rotate.
pub trait IsParallelTo {
    /// Returns true if this is parallel to the vector.
    fn is_parallel_to(&self, vector: &computed::transform::DirectionVector) -> bool;
}

impl<Number, Angle> ToCss for Rotate<Number, Angle>
where
    Number: Copy + ToCss,
    Angle: ToCss,
    (Number, Number, Number): IsParallelTo,
{
    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
    where
        W: fmt::Write,
    {
        use crate::values::computed::transform::DirectionVector;
        match *self {
            Rotate::None => dest.write_str("none"),
            Rotate::Rotate(ref angle) => angle.to_css(dest),
            Rotate::Rotate3D(x, y, z, ref angle) => {
                // If a 3d rotation is specified, the property must serialize with an axis
                // specified. If the axis is parallel with the x, y, or z axises, it must
                // serialize as the appropriate keyword.
                // https://drafts.csswg.org/css-transforms-2/#individual-transform-serialization
                let v = (x, y, z);
                if v.is_parallel_to(&DirectionVector::new(1., 0., 0.)) {
                    dest.write_char('x')?;
                } else if v.is_parallel_to(&DirectionVector::new(0., 1., 0.)) {
                    dest.write_char('y')?;
                } else if v.is_parallel_to(&DirectionVector::new(0., 0., 1.)) {
                    dest.write_char('z')?;
                } else {
                    x.to_css(dest)?;
                    dest.write_char(' ')?;
                    y.to_css(dest)?;
                    dest.write_char(' ')?;
                    z.to_css(dest)?;
                }
                dest.write_char(' ')?;
                angle.to_css(dest)
            },
        }
    }
}

#[derive(
    Clone,
    Copy,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToAnimatedZero,
    ToComputedValue,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C, u8)]
/// A value of the `Scale` property
///
/// <https://drafts.csswg.org/css-transforms-2/#individual-transforms>
pub enum GenericScale<Number> {
    /// 'none'
    None,
    /// '<number>{1,2}'
    Scale(Number, Number),
    /// '<number>{3}'
    Scale3D(Number, Number, Number),
}

pub use self::GenericScale as Scale;

impl<Number: ToCss + PartialEq> ToCss for Scale<Number> {
    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
    where
        W: fmt::Write,
    {
        match *self {
            Scale::None => dest.write_str("none"),
            Scale::Scale(ref x, ref y) => {
                x.to_css(dest)?;
                if x != y {
                    dest.write_char(' ')?;
                    y.to_css(dest)?;
                }
                Ok(())
            },
            Scale::Scale3D(ref x, ref y, ref z) => {
                x.to_css(dest)?;
                dest.write_char(' ')?;
                y.to_css(dest)?;
                dest.write_char(' ')?;
                z.to_css(dest)
            },
        }
    }
}

#[derive(
    Clone,
    Debug,
    MallocSizeOf,
    PartialEq,
    SpecifiedValueInfo,
    ToAnimatedZero,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(C, u8)]
/// A value of the `translate` property
///
/// https://drafts.csswg.org/css-transforms-2/#individual-transform-serialization:
///
/// If a 2d translation is specified, the property must serialize with only one
/// or two values (per usual, if the second value is 0px, the default, it must
/// be omitted when serializing).
///
/// If a 3d translation is specified, all three values must be serialized.
///
/// We don't omit the 3rd component even if it is 0px for now, and the
/// related spec issue is https://github.com/w3c/csswg-drafts/issues/3305
///
/// <https://drafts.csswg.org/css-transforms-2/#individual-transforms>
pub enum GenericTranslate<LengthPercentage, Length>
where
    LengthPercentage: Zero,
{
    /// 'none'
    None,
    /// '<length-percentage>' or '<length-percentage> <length-percentage>'
    Translate(
        LengthPercentage,
        #[css(skip_if = "Zero::is_zero")] LengthPercentage,
    ),
    /// '<length-percentage> <length-percentage> <length>'
    Translate3D(LengthPercentage, LengthPercentage, Length),
}

pub use self::GenericTranslate as Translate;

#[allow(missing_docs)]
#[derive(
    Clone,
    Copy,
    Debug,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
pub enum TransformStyle {
    #[cfg(feature = "servo")]
    Auto,
    Flat,
    #[css(keyword = "preserve-3d")]
    Preserve3d,
}