style/

logical_geometry.rs

/* 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/. */

//! Geometry in flow-relative space.

use crate::properties::style_structs;
use euclid::default::{Point2D, Rect, SideOffsets2D, Size2D};
use euclid::num::Zero;
use std::cmp::{max, min};
use std::fmt::{self, Debug, Error, Formatter};
use std::ops::{Add, Sub};

pub enum BlockFlowDirection {
    TopToBottom,
    RightToLeft,
    LeftToRight,
}

pub enum InlineBaseDirection {
    LeftToRight,
    RightToLeft,
}

/// The writing-mode property (different from the WritingMode enum).
/// https://drafts.csswg.org/css-writing-modes/#block-flow
/// Aliases come from https://drafts.csswg.org/css-writing-modes-4/#svg-writing-mode
#[allow(missing_docs)]
#[derive(
    Clone,
    Copy,
    Debug,
    Eq,
    FromPrimitive,
    MallocSizeOf,
    Parse,
    PartialEq,
    SpecifiedValueInfo,
    ToComputedValue,
    ToCss,
    ToResolvedValue,
    ToShmem,
)]
#[repr(u8)]
pub enum WritingModeProperty {
    #[parse(aliases = "lr,lr-tb,rl,rl-tb")]
    HorizontalTb,
    #[parse(aliases = "tb,tb-rl")]
    VerticalRl,
    VerticalLr,
    #[cfg(feature = "gecko")]
    SidewaysRl,
    #[cfg(feature = "gecko")]
    SidewaysLr,
}

// TODO: improve the readability of the WritingMode serialization, refer to the Debug:fmt()
#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, Serialize)]
#[repr(C)]
pub struct WritingMode(u8);
bitflags!(
    impl WritingMode: u8 {
        /// A vertical writing mode; writing-mode is vertical-rl,
        /// vertical-lr, sideways-lr, or sideways-rl.
        const VERTICAL = 1 << 0;
        /// The inline flow direction is reversed against the physical
        /// direction (i.e. right-to-left or bottom-to-top); writing-mode is
        /// sideways-lr or direction is rtl (but not both).
        ///
        /// (This bit can be derived from the others, but we store it for
        /// convenience.)
        const INLINE_REVERSED = 1 << 1;
        /// A vertical writing mode whose block progression direction is left-
        /// to-right; writing-mode is vertical-lr or sideways-lr.
        ///
        /// Never set without VERTICAL.
        const VERTICAL_LR = 1 << 2;
        /// The line-over/line-under sides are inverted with respect to the
        /// block-start/block-end edge; writing-mode is vertical-lr.
        ///
        /// Never set without VERTICAL and VERTICAL_LR.
        const LINE_INVERTED = 1 << 3;
        /// direction is rtl.
        const RTL = 1 << 4;
        /// All text within a vertical writing mode is displayed sideways
        /// and runs top-to-bottom or bottom-to-top; set in these cases:
        ///
        /// * writing-mode: sideways-rl;
        /// * writing-mode: sideways-lr;
        ///
        /// Never set without VERTICAL.
        const VERTICAL_SIDEWAYS = 1 << 5;
        /// Similar to VERTICAL_SIDEWAYS, but is set via text-orientation;
        /// set in these cases:
        ///
        /// * writing-mode: vertical-rl; text-orientation: sideways;
        /// * writing-mode: vertical-lr; text-orientation: sideways;
        ///
        /// Never set without VERTICAL.
        const TEXT_SIDEWAYS = 1 << 6;
        /// Horizontal text within a vertical writing mode is displayed with each
        /// glyph upright; set in these cases:
        ///
        /// * writing-mode: vertical-rl; text-orientation: upright;
        /// * writing-mode: vertical-lr: text-orientation: upright;
        ///
        /// Never set without VERTICAL.
        const UPRIGHT = 1 << 7;
    }
);

impl WritingMode {
    /// Return a WritingMode bitflags from the relevant CSS properties.
    pub fn new(inheritedbox_style: &style_structs::InheritedBox) -> Self {
        use crate::properties::longhands::direction::computed_value::T as Direction;

        let mut flags = WritingMode::empty();

        let direction = inheritedbox_style.clone_direction();
        let writing_mode = inheritedbox_style.clone_writing_mode();

        match direction {
            Direction::Ltr => {},
            Direction::Rtl => {
                flags.insert(WritingMode::RTL);
            },
        }

        match writing_mode {
            WritingModeProperty::HorizontalTb => {
                if direction == Direction::Rtl {
                    flags.insert(WritingMode::INLINE_REVERSED);
                }
            },
            WritingModeProperty::VerticalRl => {
                flags.insert(WritingMode::VERTICAL);
                if direction == Direction::Rtl {
                    flags.insert(WritingMode::INLINE_REVERSED);
                }
            },
            WritingModeProperty::VerticalLr => {
                flags.insert(WritingMode::VERTICAL);
                flags.insert(WritingMode::VERTICAL_LR);
                flags.insert(WritingMode::LINE_INVERTED);
                if direction == Direction::Rtl {
                    flags.insert(WritingMode::INLINE_REVERSED);
                }
            },
            #[cfg(feature = "gecko")]
            WritingModeProperty::SidewaysRl => {
                flags.insert(WritingMode::VERTICAL);
                flags.insert(WritingMode::VERTICAL_SIDEWAYS);
                if direction == Direction::Rtl {
                    flags.insert(WritingMode::INLINE_REVERSED);
                }
            },
            #[cfg(feature = "gecko")]
            WritingModeProperty::SidewaysLr => {
                flags.insert(WritingMode::VERTICAL);
                flags.insert(WritingMode::VERTICAL_LR);
                flags.insert(WritingMode::VERTICAL_SIDEWAYS);
                if direction == Direction::Ltr {
                    flags.insert(WritingMode::INLINE_REVERSED);
                }
            },
        }

        #[cfg(feature = "gecko")]
        {
            use crate::properties::longhands::text_orientation::computed_value::T as TextOrientation;

            // text-orientation only has an effect for vertical-rl and
            // vertical-lr values of writing-mode.
            match writing_mode {
                WritingModeProperty::VerticalRl | WritingModeProperty::VerticalLr => {
                    match inheritedbox_style.clone_text_orientation() {
                        TextOrientation::Mixed => {},
                        TextOrientation::Upright => {
                            flags.insert(WritingMode::UPRIGHT);

                            // https://drafts.csswg.org/css-writing-modes-3/#valdef-text-orientation-upright:
                            //
                            // > This value causes the used value of direction
                            // > to be ltr, and for the purposes of bidi
                            // > reordering, causes all characters to be treated
                            // > as strong LTR.
                            flags.remove(WritingMode::RTL);
                            flags.remove(WritingMode::INLINE_REVERSED);
                        },
                        TextOrientation::Sideways => {
                            flags.insert(WritingMode::TEXT_SIDEWAYS);
                        },
                    }
                },
                _ => {},
            }
        }

        flags
    }

    /// Returns the `horizontal-tb` value.
    pub fn horizontal_tb() -> Self {
        Self::empty()
    }

    #[inline]
    pub fn is_vertical(&self) -> bool {
        self.intersects(WritingMode::VERTICAL)
    }

    #[inline]
    pub fn is_horizontal(&self) -> bool {
        !self.is_vertical()
    }

    /// Assuming .is_vertical(), does the block direction go left to right?
    #[inline]
    pub fn is_vertical_lr(&self) -> bool {
        self.intersects(WritingMode::VERTICAL_LR)
    }

    /// Assuming .is_vertical(), does the inline direction go top to bottom?
    #[inline]
    pub fn is_inline_tb(&self) -> bool {
        // https://drafts.csswg.org/css-writing-modes-3/#logical-to-physical
        !self.intersects(WritingMode::INLINE_REVERSED)
    }

    #[inline]
    pub fn is_bidi_ltr(&self) -> bool {
        !self.intersects(WritingMode::RTL)
    }

    #[inline]
    pub fn is_sideways(&self) -> bool {
        self.intersects(WritingMode::VERTICAL_SIDEWAYS | WritingMode::TEXT_SIDEWAYS)
    }

    #[inline]
    pub fn is_upright(&self) -> bool {
        self.intersects(WritingMode::UPRIGHT)
    }

    /// https://drafts.csswg.org/css-writing-modes/#logical-to-physical
    ///
    /// | Return  | line-left is… | line-right is… |
    /// |---------|---------------|----------------|
    /// | `true`  | inline-start  | inline-end     |
    /// | `false` | inline-end    | inline-start   |
    #[inline]
    pub fn line_left_is_inline_start(&self) -> bool {
        // https://drafts.csswg.org/css-writing-modes/#inline-start
        // “For boxes with a used direction value of ltr, this means the line-left side.
        //  For boxes with a used direction value of rtl, this means the line-right side.”
        self.is_bidi_ltr()
    }

    #[inline]
    pub fn inline_start_physical_side(&self) -> PhysicalSide {
        match (self.is_vertical(), self.is_inline_tb(), self.is_bidi_ltr()) {
            (false, _, true) => PhysicalSide::Left,
            (false, _, false) => PhysicalSide::Right,
            (true, true, _) => PhysicalSide::Top,
            (true, false, _) => PhysicalSide::Bottom,
        }
    }

    #[inline]
    pub fn inline_end_physical_side(&self) -> PhysicalSide {
        match (self.is_vertical(), self.is_inline_tb(), self.is_bidi_ltr()) {
            (false, _, true) => PhysicalSide::Right,
            (false, _, false) => PhysicalSide::Left,
            (true, true, _) => PhysicalSide::Bottom,
            (true, false, _) => PhysicalSide::Top,
        }
    }

    #[inline]
    pub fn block_start_physical_side(&self) -> PhysicalSide {
        match (self.is_vertical(), self.is_vertical_lr()) {
            (false, _) => PhysicalSide::Top,
            (true, true) => PhysicalSide::Left,
            (true, false) => PhysicalSide::Right,
        }
    }

    #[inline]
    pub fn block_end_physical_side(&self) -> PhysicalSide {
        match (self.is_vertical(), self.is_vertical_lr()) {
            (false, _) => PhysicalSide::Bottom,
            (true, true) => PhysicalSide::Right,
            (true, false) => PhysicalSide::Left,
        }
    }

    #[inline]
    pub fn start_start_physical_corner(&self) -> PhysicalCorner {
        PhysicalCorner::from_sides(
            self.block_start_physical_side(),
            self.inline_start_physical_side(),
        )
    }

    #[inline]
    pub fn start_end_physical_corner(&self) -> PhysicalCorner {
        PhysicalCorner::from_sides(
            self.block_start_physical_side(),
            self.inline_end_physical_side(),
        )
    }

    #[inline]
    pub fn end_start_physical_corner(&self) -> PhysicalCorner {
        PhysicalCorner::from_sides(
            self.block_end_physical_side(),
            self.inline_start_physical_side(),
        )
    }

    #[inline]
    pub fn end_end_physical_corner(&self) -> PhysicalCorner {
        PhysicalCorner::from_sides(
            self.block_end_physical_side(),
            self.inline_end_physical_side(),
        )
    }

    #[inline]
    pub fn block_flow_direction(&self) -> BlockFlowDirection {
        match (self.is_vertical(), self.is_vertical_lr()) {
            (false, _) => BlockFlowDirection::TopToBottom,
            (true, true) => BlockFlowDirection::LeftToRight,
            (true, false) => BlockFlowDirection::RightToLeft,
        }
    }

    #[inline]
    pub fn inline_base_direction(&self) -> InlineBaseDirection {
        if self.intersects(WritingMode::RTL) {
            InlineBaseDirection::RightToLeft
        } else {
            InlineBaseDirection::LeftToRight
        }
    }

    #[inline]
    /// Is the text layout vertical?
    pub fn is_text_vertical(&self) -> bool {
        self.is_vertical() && !self.is_sideways()
    }
}

impl fmt::Display for WritingMode {
    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
        if self.is_vertical() {
            write!(formatter, "V")?;
            if self.is_vertical_lr() {
                write!(formatter, " LR")?;
            } else {
                write!(formatter, " RL")?;
            }
            if self.is_sideways() {
                write!(formatter, " Sideways")?;
            }
            if self.intersects(WritingMode::LINE_INVERTED) {
                write!(formatter, " Inverted")?;
            }
        } else {
            write!(formatter, "H")?;
        }
        if self.is_bidi_ltr() {
            write!(formatter, " LTR")
        } else {
            write!(formatter, " RTL")
        }
    }
}

/// Wherever logical geometry is used, the writing mode is known based on context:
/// every method takes a `mode` parameter.
/// However, this context is easy to get wrong.
/// In debug builds only, logical geometry objects store their writing mode
/// (in addition to taking it as a parameter to methods) and check it.
/// In non-debug builds, make this storage zero-size and the checks no-ops.
#[cfg(not(debug_assertions))]
#[derive(Clone, Copy, Eq, PartialEq)]
#[cfg_attr(feature = "servo", derive(Serialize))]
struct DebugWritingMode;

#[cfg(debug_assertions)]
#[derive(Clone, Copy, Eq, PartialEq)]
#[cfg_attr(feature = "servo", derive(Serialize))]
struct DebugWritingMode {
    mode: WritingMode,
}

#[cfg(not(debug_assertions))]
impl DebugWritingMode {
    #[inline]
    fn check(&self, _other: WritingMode) {}

    #[inline]
    fn check_debug(&self, _other: DebugWritingMode) {}

    #[inline]
    fn new(_mode: WritingMode) -> DebugWritingMode {
        DebugWritingMode
    }
}

#[cfg(debug_assertions)]
impl DebugWritingMode {
    #[inline]
    fn check(&self, other: WritingMode) {
        assert_eq!(self.mode, other)
    }

    #[inline]
    fn check_debug(&self, other: DebugWritingMode) {
        assert_eq!(self.mode, other.mode)
    }

    #[inline]
    fn new(mode: WritingMode) -> DebugWritingMode {
        DebugWritingMode { mode }
    }
}

impl Debug for DebugWritingMode {
    #[cfg(not(debug_assertions))]
    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
        write!(formatter, "?")
    }

    #[cfg(debug_assertions)]
    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
        write!(formatter, "{}", self.mode)
    }
}

// Used to specify the logical direction.
#[derive(Clone, Copy, Debug, PartialEq)]
#[cfg_attr(feature = "servo", derive(Serialize))]
pub enum Direction {
    Inline,
    Block,
}

/// A 2D size in flow-relative dimensions
#[derive(Clone, Copy, Eq, PartialEq)]
#[cfg_attr(feature = "servo", derive(Serialize))]
pub struct LogicalSize<T> {
    pub inline: T, // inline-size, a.k.a. logical width, a.k.a. measure
    pub block: T,  // block-size, a.k.a. logical height, a.k.a. extent
    debug_writing_mode: DebugWritingMode,
}

impl<T: Debug> Debug for LogicalSize<T> {
    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
        write!(
            formatter,
            "LogicalSize({:?}, i{:?}×b{:?})",
            self.debug_writing_mode, self.inline, self.block
        )
    }
}

// Can not implement the Zero trait: its zero() method does not have the `mode` parameter.
impl<T: Zero> LogicalSize<T> {
    #[inline]
    pub fn zero(mode: WritingMode) -> LogicalSize<T> {
        LogicalSize {
            inline: Zero::zero(),
            block: Zero::zero(),
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }
}

impl<T> LogicalSize<T> {
    #[inline]
    pub fn new(mode: WritingMode, inline: T, block: T) -> LogicalSize<T> {
        LogicalSize {
            inline: inline,
            block: block,
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }

    #[inline]
    pub fn from_physical(mode: WritingMode, size: Size2D<T>) -> LogicalSize<T> {
        if mode.is_vertical() {
            LogicalSize::new(mode, size.height, size.width)
        } else {
            LogicalSize::new(mode, size.width, size.height)
        }
    }
}

impl<T: Clone> LogicalSize<T> {
    #[inline]
    pub fn width(&self, mode: WritingMode) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            self.block.clone()
        } else {
            self.inline.clone()
        }
    }

    #[inline]
    pub fn set_width(&mut self, mode: WritingMode, width: T) {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            self.block = width
        } else {
            self.inline = width
        }
    }

    #[inline]
    pub fn height(&self, mode: WritingMode) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            self.inline.clone()
        } else {
            self.block.clone()
        }
    }

    #[inline]
    pub fn set_height(&mut self, mode: WritingMode, height: T) {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            self.inline = height
        } else {
            self.block = height
        }
    }

    #[inline]
    pub fn to_physical(&self, mode: WritingMode) -> Size2D<T> {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            Size2D::new(self.block.clone(), self.inline.clone())
        } else {
            Size2D::new(self.inline.clone(), self.block.clone())
        }
    }

    #[inline]
    pub fn convert(&self, mode_from: WritingMode, mode_to: WritingMode) -> LogicalSize<T> {
        if mode_from == mode_to {
            self.debug_writing_mode.check(mode_from);
            self.clone()
        } else {
            LogicalSize::from_physical(mode_to, self.to_physical(mode_from))
        }
    }
}

impl<T: Add<T, Output = T>> Add for LogicalSize<T> {
    type Output = LogicalSize<T>;

    #[inline]
    fn add(self, other: LogicalSize<T>) -> LogicalSize<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalSize {
            debug_writing_mode: self.debug_writing_mode,
            inline: self.inline + other.inline,
            block: self.block + other.block,
        }
    }
}

impl<T: Sub<T, Output = T>> Sub for LogicalSize<T> {
    type Output = LogicalSize<T>;

    #[inline]
    fn sub(self, other: LogicalSize<T>) -> LogicalSize<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalSize {
            debug_writing_mode: self.debug_writing_mode,
            inline: self.inline - other.inline,
            block: self.block - other.block,
        }
    }
}

/// A 2D point in flow-relative dimensions
#[derive(Clone, Copy, Eq, PartialEq)]
#[cfg_attr(feature = "servo", derive(Serialize))]
pub struct LogicalPoint<T> {
    /// inline-axis coordinate
    pub i: T,
    /// block-axis coordinate
    pub b: T,
    debug_writing_mode: DebugWritingMode,
}

impl<T: Debug> Debug for LogicalPoint<T> {
    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
        write!(
            formatter,
            "LogicalPoint({:?} (i{:?}, b{:?}))",
            self.debug_writing_mode, self.i, self.b
        )
    }
}

// Can not implement the Zero trait: its zero() method does not have the `mode` parameter.
impl<T: Zero> LogicalPoint<T> {
    #[inline]
    pub fn zero(mode: WritingMode) -> LogicalPoint<T> {
        LogicalPoint {
            i: Zero::zero(),
            b: Zero::zero(),
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }
}

impl<T: Copy> LogicalPoint<T> {
    #[inline]
    pub fn new(mode: WritingMode, i: T, b: T) -> LogicalPoint<T> {
        LogicalPoint {
            i: i,
            b: b,
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }
}

impl<T: Copy + Sub<T, Output = T>> LogicalPoint<T> {
    #[inline]
    pub fn from_physical(
        mode: WritingMode,
        point: Point2D<T>,
        container_size: Size2D<T>,
    ) -> LogicalPoint<T> {
        if mode.is_vertical() {
            LogicalPoint {
                i: if mode.is_inline_tb() {
                    point.y
                } else {
                    container_size.height - point.y
                },
                b: if mode.is_vertical_lr() {
                    point.x
                } else {
                    container_size.width - point.x
                },
                debug_writing_mode: DebugWritingMode::new(mode),
            }
        } else {
            LogicalPoint {
                i: if mode.is_bidi_ltr() {
                    point.x
                } else {
                    container_size.width - point.x
                },
                b: point.y,
                debug_writing_mode: DebugWritingMode::new(mode),
            }
        }
    }

    #[inline]
    pub fn x(&self, mode: WritingMode, container_size: Size2D<T>) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_vertical_lr() {
                self.b
            } else {
                container_size.width - self.b
            }
        } else {
            if mode.is_bidi_ltr() {
                self.i
            } else {
                container_size.width - self.i
            }
        }
    }

    #[inline]
    pub fn set_x(&mut self, mode: WritingMode, x: T, container_size: Size2D<T>) {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            self.b = if mode.is_vertical_lr() {
                x
            } else {
                container_size.width - x
            }
        } else {
            self.i = if mode.is_bidi_ltr() {
                x
            } else {
                container_size.width - x
            }
        }
    }

    #[inline]
    pub fn y(&self, mode: WritingMode, container_size: Size2D<T>) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_inline_tb() {
                self.i
            } else {
                container_size.height - self.i
            }
        } else {
            self.b
        }
    }

    #[inline]
    pub fn set_y(&mut self, mode: WritingMode, y: T, container_size: Size2D<T>) {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            self.i = if mode.is_inline_tb() {
                y
            } else {
                container_size.height - y
            }
        } else {
            self.b = y
        }
    }

    #[inline]
    pub fn to_physical(&self, mode: WritingMode, container_size: Size2D<T>) -> Point2D<T> {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            Point2D::new(
                if mode.is_vertical_lr() {
                    self.b
                } else {
                    container_size.width - self.b
                },
                if mode.is_inline_tb() {
                    self.i
                } else {
                    container_size.height - self.i
                },
            )
        } else {
            Point2D::new(
                if mode.is_bidi_ltr() {
                    self.i
                } else {
                    container_size.width - self.i
                },
                self.b,
            )
        }
    }

    #[inline]
    pub fn convert(
        &self,
        mode_from: WritingMode,
        mode_to: WritingMode,
        container_size: Size2D<T>,
    ) -> LogicalPoint<T> {
        if mode_from == mode_to {
            self.debug_writing_mode.check(mode_from);
            *self
        } else {
            LogicalPoint::from_physical(
                mode_to,
                self.to_physical(mode_from, container_size),
                container_size,
            )
        }
    }
}

impl<T: Copy + Add<T, Output = T>> LogicalPoint<T> {
    /// This doesn’t really makes sense,
    /// but happens when dealing with multiple origins.
    #[inline]
    pub fn add_point(&self, other: &LogicalPoint<T>) -> LogicalPoint<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalPoint {
            debug_writing_mode: self.debug_writing_mode,
            i: self.i + other.i,
            b: self.b + other.b,
        }
    }
}

impl<T: Copy + Add<T, Output = T>> Add<LogicalSize<T>> for LogicalPoint<T> {
    type Output = LogicalPoint<T>;

    #[inline]
    fn add(self, other: LogicalSize<T>) -> LogicalPoint<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalPoint {
            debug_writing_mode: self.debug_writing_mode,
            i: self.i + other.inline,
            b: self.b + other.block,
        }
    }
}

impl<T: Copy + Sub<T, Output = T>> Sub<LogicalSize<T>> for LogicalPoint<T> {
    type Output = LogicalPoint<T>;

    #[inline]
    fn sub(self, other: LogicalSize<T>) -> LogicalPoint<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalPoint {
            debug_writing_mode: self.debug_writing_mode,
            i: self.i - other.inline,
            b: self.b - other.block,
        }
    }
}

/// A "margin" in flow-relative dimensions
/// Represents the four sides of the margins, borders, or padding of a CSS box,
/// or a combination of those.
/// A positive "margin" can be added to a rectangle to obtain a bigger rectangle.
#[derive(Clone, Copy, Eq, PartialEq)]
#[cfg_attr(feature = "servo", derive(Serialize))]
pub struct LogicalMargin<T> {
    pub block_start: T,
    pub inline_end: T,
    pub block_end: T,
    pub inline_start: T,
    debug_writing_mode: DebugWritingMode,
}

impl<T: Debug> Debug for LogicalMargin<T> {
    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
        let writing_mode_string = if cfg!(debug_assertions) {
            format!("{:?}, ", self.debug_writing_mode)
        } else {
            "".to_owned()
        };

        write!(
            formatter,
            "LogicalMargin({}i:{:?}..{:?} b:{:?}..{:?})",
            writing_mode_string,
            self.inline_start,
            self.inline_end,
            self.block_start,
            self.block_end
        )
    }
}

impl<T: Zero> LogicalMargin<T> {
    #[inline]
    pub fn zero(mode: WritingMode) -> LogicalMargin<T> {
        LogicalMargin {
            block_start: Zero::zero(),
            inline_end: Zero::zero(),
            block_end: Zero::zero(),
            inline_start: Zero::zero(),
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }
}

impl<T> LogicalMargin<T> {
    #[inline]
    pub fn new(
        mode: WritingMode,
        block_start: T,
        inline_end: T,
        block_end: T,
        inline_start: T,
    ) -> LogicalMargin<T> {
        LogicalMargin {
            block_start,
            inline_end,
            block_end,
            inline_start,
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }

    #[inline]
    pub fn from_physical(mode: WritingMode, offsets: SideOffsets2D<T>) -> LogicalMargin<T> {
        let block_start;
        let inline_end;
        let block_end;
        let inline_start;
        if mode.is_vertical() {
            if mode.is_vertical_lr() {
                block_start = offsets.left;
                block_end = offsets.right;
            } else {
                block_start = offsets.right;
                block_end = offsets.left;
            }
            if mode.is_inline_tb() {
                inline_start = offsets.top;
                inline_end = offsets.bottom;
            } else {
                inline_start = offsets.bottom;
                inline_end = offsets.top;
            }
        } else {
            block_start = offsets.top;
            block_end = offsets.bottom;
            if mode.is_bidi_ltr() {
                inline_start = offsets.left;
                inline_end = offsets.right;
            } else {
                inline_start = offsets.right;
                inline_end = offsets.left;
            }
        }
        LogicalMargin::new(mode, block_start, inline_end, block_end, inline_start)
    }
}

impl<T: Clone> LogicalMargin<T> {
    #[inline]
    pub fn new_all_same(mode: WritingMode, value: T) -> LogicalMargin<T> {
        LogicalMargin::new(mode, value.clone(), value.clone(), value.clone(), value)
    }

    #[inline]
    pub fn top(&self, mode: WritingMode) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_inline_tb() {
                self.inline_start.clone()
            } else {
                self.inline_end.clone()
            }
        } else {
            self.block_start.clone()
        }
    }

    #[inline]
    pub fn set_top(&mut self, mode: WritingMode, top: T) {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_inline_tb() {
                self.inline_start = top
            } else {
                self.inline_end = top
            }
        } else {
            self.block_start = top
        }
    }

    #[inline]
    pub fn right(&self, mode: WritingMode) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_vertical_lr() {
                self.block_end.clone()
            } else {
                self.block_start.clone()
            }
        } else {
            if mode.is_bidi_ltr() {
                self.inline_end.clone()
            } else {
                self.inline_start.clone()
            }
        }
    }

    #[inline]
    pub fn set_right(&mut self, mode: WritingMode, right: T) {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_vertical_lr() {
                self.block_end = right
            } else {
                self.block_start = right
            }
        } else {
            if mode.is_bidi_ltr() {
                self.inline_end = right
            } else {
                self.inline_start = right
            }
        }
    }

    #[inline]
    pub fn bottom(&self, mode: WritingMode) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_inline_tb() {
                self.inline_end.clone()
            } else {
                self.inline_start.clone()
            }
        } else {
            self.block_end.clone()
        }
    }

    #[inline]
    pub fn set_bottom(&mut self, mode: WritingMode, bottom: T) {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_inline_tb() {
                self.inline_end = bottom
            } else {
                self.inline_start = bottom
            }
        } else {
            self.block_end = bottom
        }
    }

    #[inline]
    pub fn left(&self, mode: WritingMode) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_vertical_lr() {
                self.block_start.clone()
            } else {
                self.block_end.clone()
            }
        } else {
            if mode.is_bidi_ltr() {
                self.inline_start.clone()
            } else {
                self.inline_end.clone()
            }
        }
    }

    #[inline]
    pub fn set_left(&mut self, mode: WritingMode, left: T) {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            if mode.is_vertical_lr() {
                self.block_start = left
            } else {
                self.block_end = left
            }
        } else {
            if mode.is_bidi_ltr() {
                self.inline_start = left
            } else {
                self.inline_end = left
            }
        }
    }

    #[inline]
    pub fn to_physical(&self, mode: WritingMode) -> SideOffsets2D<T> {
        self.debug_writing_mode.check(mode);
        let top;
        let right;
        let bottom;
        let left;
        if mode.is_vertical() {
            if mode.is_vertical_lr() {
                left = self.block_start.clone();
                right = self.block_end.clone();
            } else {
                right = self.block_start.clone();
                left = self.block_end.clone();
            }
            if mode.is_inline_tb() {
                top = self.inline_start.clone();
                bottom = self.inline_end.clone();
            } else {
                bottom = self.inline_start.clone();
                top = self.inline_end.clone();
            }
        } else {
            top = self.block_start.clone();
            bottom = self.block_end.clone();
            if mode.is_bidi_ltr() {
                left = self.inline_start.clone();
                right = self.inline_end.clone();
            } else {
                right = self.inline_start.clone();
                left = self.inline_end.clone();
            }
        }
        SideOffsets2D::new(top, right, bottom, left)
    }

    #[inline]
    pub fn convert(&self, mode_from: WritingMode, mode_to: WritingMode) -> LogicalMargin<T> {
        if mode_from == mode_to {
            self.debug_writing_mode.check(mode_from);
            self.clone()
        } else {
            LogicalMargin::from_physical(mode_to, self.to_physical(mode_from))
        }
    }
}

impl<T: PartialEq + Zero> LogicalMargin<T> {
    #[inline]
    pub fn is_zero(&self) -> bool {
        self.block_start == Zero::zero() &&
            self.inline_end == Zero::zero() &&
            self.block_end == Zero::zero() &&
            self.inline_start == Zero::zero()
    }
}

impl<T: Copy + Add<T, Output = T>> LogicalMargin<T> {
    #[inline]
    pub fn inline_start_end(&self) -> T {
        self.inline_start + self.inline_end
    }

    #[inline]
    pub fn block_start_end(&self) -> T {
        self.block_start + self.block_end
    }

    #[inline]
    pub fn start_end(&self, direction: Direction) -> T {
        match direction {
            Direction::Inline => self.inline_start + self.inline_end,
            Direction::Block => self.block_start + self.block_end,
        }
    }

    #[inline]
    pub fn top_bottom(&self, mode: WritingMode) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            self.inline_start_end()
        } else {
            self.block_start_end()
        }
    }

    #[inline]
    pub fn left_right(&self, mode: WritingMode) -> T {
        self.debug_writing_mode.check(mode);
        if mode.is_vertical() {
            self.block_start_end()
        } else {
            self.inline_start_end()
        }
    }
}

impl<T: Add<T, Output = T>> Add for LogicalMargin<T> {
    type Output = LogicalMargin<T>;

    #[inline]
    fn add(self, other: LogicalMargin<T>) -> LogicalMargin<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalMargin {
            debug_writing_mode: self.debug_writing_mode,
            block_start: self.block_start + other.block_start,
            inline_end: self.inline_end + other.inline_end,
            block_end: self.block_end + other.block_end,
            inline_start: self.inline_start + other.inline_start,
        }
    }
}

impl<T: Sub<T, Output = T>> Sub for LogicalMargin<T> {
    type Output = LogicalMargin<T>;

    #[inline]
    fn sub(self, other: LogicalMargin<T>) -> LogicalMargin<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalMargin {
            debug_writing_mode: self.debug_writing_mode,
            block_start: self.block_start - other.block_start,
            inline_end: self.inline_end - other.inline_end,
            block_end: self.block_end - other.block_end,
            inline_start: self.inline_start - other.inline_start,
        }
    }
}

/// A rectangle in flow-relative dimensions
#[derive(Clone, Copy, Eq, PartialEq)]
#[cfg_attr(feature = "servo", derive(Serialize))]
pub struct LogicalRect<T> {
    pub start: LogicalPoint<T>,
    pub size: LogicalSize<T>,
    debug_writing_mode: DebugWritingMode,
}

impl<T: Debug> Debug for LogicalRect<T> {
    fn fmt(&self, formatter: &mut Formatter) -> Result<(), Error> {
        let writing_mode_string = if cfg!(debug_assertions) {
            format!("{:?}, ", self.debug_writing_mode)
        } else {
            "".to_owned()
        };

        write!(
            formatter,
            "LogicalRect({}i{:?}×b{:?}, @ (i{:?},b{:?}))",
            writing_mode_string, self.size.inline, self.size.block, self.start.i, self.start.b
        )
    }
}

impl<T: Zero> LogicalRect<T> {
    #[inline]
    pub fn zero(mode: WritingMode) -> LogicalRect<T> {
        LogicalRect {
            start: LogicalPoint::zero(mode),
            size: LogicalSize::zero(mode),
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }
}

impl<T: Copy> LogicalRect<T> {
    #[inline]
    pub fn new(
        mode: WritingMode,
        inline_start: T,
        block_start: T,
        inline: T,
        block: T,
    ) -> LogicalRect<T> {
        LogicalRect {
            start: LogicalPoint::new(mode, inline_start, block_start),
            size: LogicalSize::new(mode, inline, block),
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }

    #[inline]
    pub fn from_point_size(
        mode: WritingMode,
        start: LogicalPoint<T>,
        size: LogicalSize<T>,
    ) -> LogicalRect<T> {
        start.debug_writing_mode.check(mode);
        size.debug_writing_mode.check(mode);
        LogicalRect {
            start: start,
            size: size,
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }
}

impl<T: Copy + Add<T, Output = T> + Sub<T, Output = T>> LogicalRect<T> {
    #[inline]
    pub fn from_physical(
        mode: WritingMode,
        rect: Rect<T>,
        container_size: Size2D<T>,
    ) -> LogicalRect<T> {
        let inline_start;
        let block_start;
        let inline;
        let block;
        if mode.is_vertical() {
            inline = rect.size.height;
            block = rect.size.width;
            if mode.is_vertical_lr() {
                block_start = rect.origin.x;
            } else {
                block_start = container_size.width - (rect.origin.x + rect.size.width);
            }
            if mode.is_inline_tb() {
                inline_start = rect.origin.y;
            } else {
                inline_start = container_size.height - (rect.origin.y + rect.size.height);
            }
        } else {
            inline = rect.size.width;
            block = rect.size.height;
            block_start = rect.origin.y;
            if mode.is_bidi_ltr() {
                inline_start = rect.origin.x;
            } else {
                inline_start = container_size.width - (rect.origin.x + rect.size.width);
            }
        }
        LogicalRect {
            start: LogicalPoint::new(mode, inline_start, block_start),
            size: LogicalSize::new(mode, inline, block),
            debug_writing_mode: DebugWritingMode::new(mode),
        }
    }

    #[inline]
    pub fn inline_end(&self) -> T {
        self.start.i + self.size.inline
    }

    #[inline]
    pub fn block_end(&self) -> T {
        self.start.b + self.size.block
    }

    #[inline]
    pub fn to_physical(&self, mode: WritingMode, container_size: Size2D<T>) -> Rect<T> {
        self.debug_writing_mode.check(mode);
        let x;
        let y;
        let width;
        let height;
        if mode.is_vertical() {
            width = self.size.block;
            height = self.size.inline;
            if mode.is_vertical_lr() {
                x = self.start.b;
            } else {
                x = container_size.width - self.block_end();
            }
            if mode.is_inline_tb() {
                y = self.start.i;
            } else {
                y = container_size.height - self.inline_end();
            }
        } else {
            width = self.size.inline;
            height = self.size.block;
            y = self.start.b;
            if mode.is_bidi_ltr() {
                x = self.start.i;
            } else {
                x = container_size.width - self.inline_end();
            }
        }
        Rect {
            origin: Point2D::new(x, y),
            size: Size2D::new(width, height),
        }
    }

    #[inline]
    pub fn convert(
        &self,
        mode_from: WritingMode,
        mode_to: WritingMode,
        container_size: Size2D<T>,
    ) -> LogicalRect<T> {
        if mode_from == mode_to {
            self.debug_writing_mode.check(mode_from);
            *self
        } else {
            LogicalRect::from_physical(
                mode_to,
                self.to_physical(mode_from, container_size),
                container_size,
            )
        }
    }

    pub fn translate_by_size(&self, offset: LogicalSize<T>) -> LogicalRect<T> {
        LogicalRect {
            start: self.start + offset,
            ..*self
        }
    }

    pub fn translate(&self, offset: &LogicalPoint<T>) -> LogicalRect<T> {
        LogicalRect {
            start: self.start +
                LogicalSize {
                    inline: offset.i,
                    block: offset.b,
                    debug_writing_mode: offset.debug_writing_mode,
                },
            size: self.size,
            debug_writing_mode: self.debug_writing_mode,
        }
    }
}

impl<T: Copy + Ord + Add<T, Output = T> + Sub<T, Output = T>> LogicalRect<T> {
    #[inline]
    pub fn union(&self, other: &LogicalRect<T>) -> LogicalRect<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);

        let inline_start = min(self.start.i, other.start.i);
        let block_start = min(self.start.b, other.start.b);
        LogicalRect {
            start: LogicalPoint {
                i: inline_start,
                b: block_start,
                debug_writing_mode: self.debug_writing_mode,
            },
            size: LogicalSize {
                inline: max(self.inline_end(), other.inline_end()) - inline_start,
                block: max(self.block_end(), other.block_end()) - block_start,
                debug_writing_mode: self.debug_writing_mode,
            },
            debug_writing_mode: self.debug_writing_mode,
        }
    }
}

impl<T: Copy + Add<T, Output = T> + Sub<T, Output = T>> Add<LogicalMargin<T>> for LogicalRect<T> {
    type Output = LogicalRect<T>;

    #[inline]
    fn add(self, other: LogicalMargin<T>) -> LogicalRect<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalRect {
            start: LogicalPoint {
                // Growing a rectangle on the start side means pushing its
                // start point on the negative direction.
                i: self.start.i - other.inline_start,
                b: self.start.b - other.block_start,
                debug_writing_mode: self.debug_writing_mode,
            },
            size: LogicalSize {
                inline: self.size.inline + other.inline_start_end(),
                block: self.size.block + other.block_start_end(),
                debug_writing_mode: self.debug_writing_mode,
            },
            debug_writing_mode: self.debug_writing_mode,
        }
    }
}

impl<T: Copy + Add<T, Output = T> + Sub<T, Output = T>> Sub<LogicalMargin<T>> for LogicalRect<T> {
    type Output = LogicalRect<T>;

    #[inline]
    fn sub(self, other: LogicalMargin<T>) -> LogicalRect<T> {
        self.debug_writing_mode
            .check_debug(other.debug_writing_mode);
        LogicalRect {
            start: LogicalPoint {
                // Shrinking a rectangle on the start side means pushing its
                // start point on the positive direction.
                i: self.start.i + other.inline_start,
                b: self.start.b + other.block_start,
                debug_writing_mode: self.debug_writing_mode,
            },
            size: LogicalSize {
                inline: self.size.inline - other.inline_start_end(),
                block: self.size.block - other.block_start_end(),
                debug_writing_mode: self.debug_writing_mode,
            },
            debug_writing_mode: self.debug_writing_mode,
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(u8)]
pub enum LogicalAxis {
    Block = 0,
    Inline,
}

impl LogicalAxis {
    #[inline]
    pub fn to_physical(self, wm: WritingMode) -> PhysicalAxis {
        if wm.is_horizontal() == (self == Self::Inline) {
            PhysicalAxis::Horizontal
        } else {
            PhysicalAxis::Vertical
        }
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(u8)]
pub enum LogicalSide {
    BlockStart = 0,
    BlockEnd,
    InlineStart,
    InlineEnd,
}

impl LogicalSide {
    fn is_block(self) -> bool {
        matches!(self, Self::BlockStart | Self::BlockEnd)
    }

    #[inline]
    pub fn to_physical(self, wm: WritingMode) -> PhysicalSide {
        // Block mapping depends only on vertical+vertical-lr
        static BLOCK_MAPPING: [[PhysicalSide; 2]; 4] = [
            [PhysicalSide::Top, PhysicalSide::Bottom], // horizontal-tb
            [PhysicalSide::Right, PhysicalSide::Left], // vertical-rl
            [PhysicalSide::Bottom, PhysicalSide::Top], // (horizontal-bt)
            [PhysicalSide::Left, PhysicalSide::Right], // vertical-lr
        ];

        if self.is_block() {
            let vertical = wm.is_vertical();
            let lr = wm.is_vertical_lr();
            let index = (vertical as usize) | ((lr as usize) << 1);
            return BLOCK_MAPPING[index][self as usize];
        }

        // start = 0, end = 1
        let edge = self as usize - 2;
        // Inline axis sides depend on all three of writing-mode, text-orientation and direction,
        // which are encoded in the VERTICAL, INLINE_REVERSED, VERTICAL_LR and LINE_INVERTED bits.
        //
        //   bit 0 = the VERTICAL value
        //   bit 1 = the INLINE_REVERSED value
        //   bit 2 = the VERTICAL_LR value
        //   bit 3 = the LINE_INVERTED value
        //
        // Note that not all of these combinations can actually be specified via CSS: there is no
        // horizontal-bt writing-mode, and no text-orientation value that produces "inverted"
        // text. (The former 'sideways-left' value, no longer in the spec, would have produced
        // this in vertical-rl mode.)
        static INLINE_MAPPING: [[PhysicalSide; 2]; 16] = [
            [PhysicalSide::Left, PhysicalSide::Right], // horizontal-tb               ltr
            [PhysicalSide::Top, PhysicalSide::Bottom], // vertical-rl                 ltr
            [PhysicalSide::Right, PhysicalSide::Left], // horizontal-tb               rtl
            [PhysicalSide::Bottom, PhysicalSide::Top], // vertical-rl                 rtl
            [PhysicalSide::Right, PhysicalSide::Left], // (horizontal-bt)  (inverted) ltr
            [PhysicalSide::Top, PhysicalSide::Bottom], // sideways-lr                 rtl
            [PhysicalSide::Left, PhysicalSide::Right], // (horizontal-bt)  (inverted) rtl
            [PhysicalSide::Bottom, PhysicalSide::Top], // sideways-lr                 ltr
            [PhysicalSide::Left, PhysicalSide::Right], // horizontal-tb    (inverted) rtl
            [PhysicalSide::Top, PhysicalSide::Bottom], // vertical-rl      (inverted) rtl
            [PhysicalSide::Right, PhysicalSide::Left], // horizontal-tb    (inverted) ltr
            [PhysicalSide::Bottom, PhysicalSide::Top], // vertical-rl      (inverted) ltr
            [PhysicalSide::Left, PhysicalSide::Right], // (horizontal-bt)             ltr
            [PhysicalSide::Top, PhysicalSide::Bottom], // vertical-lr                 ltr
            [PhysicalSide::Right, PhysicalSide::Left], // (horizontal-bt)             rtl
            [PhysicalSide::Bottom, PhysicalSide::Top], // vertical-lr                 rtl
        ];

        debug_assert!(
            WritingMode::VERTICAL.bits() == 0x01 &&
                WritingMode::INLINE_REVERSED.bits() == 0x02 &&
                WritingMode::VERTICAL_LR.bits() == 0x04 &&
                WritingMode::LINE_INVERTED.bits() == 0x08
        );
        let index = (wm.bits() & 0xF) as usize;
        INLINE_MAPPING[index][edge]
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(u8)]
pub enum LogicalCorner {
    StartStart = 0,
    StartEnd,
    EndStart,
    EndEnd,
}

impl LogicalCorner {
    #[inline]
    pub fn to_physical(self, wm: WritingMode) -> PhysicalCorner {
        static CORNER_TO_SIDES: [[LogicalSide; 2]; 4] = [
            [LogicalSide::BlockStart, LogicalSide::InlineStart],
            [LogicalSide::BlockStart, LogicalSide::InlineEnd],
            [LogicalSide::BlockEnd, LogicalSide::InlineStart],
            [LogicalSide::BlockEnd, LogicalSide::InlineEnd],
        ];

        let [block, inline] = CORNER_TO_SIDES[self as usize];
        let block = block.to_physical(wm);
        let inline = inline.to_physical(wm);
        PhysicalCorner::from_sides(block, inline)
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(u8)]
pub enum PhysicalAxis {
    Vertical = 0,
    Horizontal,
}

#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(u8)]
pub enum PhysicalSide {
    Top = 0,
    Right,
    Bottom,
    Left,
}

impl PhysicalSide {
    fn orthogonal_to(self, other: Self) -> bool {
        matches!(self, Self::Top | Self::Bottom) != matches!(other, Self::Top | Self::Bottom)
    }
}

#[derive(Clone, Copy, Debug, PartialEq)]
#[repr(u8)]
pub enum PhysicalCorner {
    TopLeft = 0,
    TopRight,
    BottomRight,
    BottomLeft,
}

impl PhysicalCorner {
    fn from_sides(a: PhysicalSide, b: PhysicalSide) -> Self {
        debug_assert!(a.orthogonal_to(b), "Sides should be orthogonal");
        // Only some of these are possible, since we expect only orthogonal values. If the two
        // sides were to be parallel, we fall back to returning TopLeft.
        const IMPOSSIBLE: PhysicalCorner = PhysicalCorner::TopLeft;
        static SIDES_TO_CORNER: [[PhysicalCorner; 4]; 4] = [
            [
                IMPOSSIBLE,
                PhysicalCorner::TopRight,
                IMPOSSIBLE,
                PhysicalCorner::TopLeft,
            ],
            [
                PhysicalCorner::TopRight,
                IMPOSSIBLE,
                PhysicalCorner::BottomRight,
                IMPOSSIBLE,
            ],
            [
                IMPOSSIBLE,
                PhysicalCorner::BottomRight,
                IMPOSSIBLE,
                PhysicalCorner::BottomLeft,
            ],
            [
                PhysicalCorner::TopLeft,
                IMPOSSIBLE,
                PhysicalCorner::BottomLeft,
                IMPOSSIBLE,
            ],
        ];
        SIDES_TO_CORNER[a as usize][b as usize]
    }
}