Add logical geometry primitives, for CSS Writing Modes.

3 files changed, 995 insertions, 0 deletions

diff --git a/src/components/style/properties/mod.rs.mako b/src/components/style/properties/mod.rs.mako
index 3157ac8c5fd..55ec83cc038 100644
--- a/src/components/style/properties/mod.rs.mako
+++ b/src/components/style/properties/mod.rs.mako
@@ -1035,6 +1035,17 @@ pub mod longhands {
     ${single_keyword("table-layout", "auto fixed")}
 
     // CSS 2.1, Section 18 - User interface
+
+
+    // CSS Writing Modes Level 3
+    // http://dev.w3.org/csswg/css-writing-modes/
+    ${switch_to_style_struct("InheritedBox")}
+
+    ${single_keyword("writing-mode", "horizontal-tb vertical-rl vertical-lr")}
+
+    // FIXME(SimonSapin): Add 'mixed' and 'upright' (needs vertical text support)
+    // FIXME(SimonSapin): initial (first) value should be 'mixed', when that's implemented
+    ${single_keyword("text-orientation", "sideways sideways-left sideways-right")}
 }
 
 
@@ -1565,6 +1576,9 @@ impl PropertyDeclaration {
 
 pub mod style_structs {
     use super::longhands;
+    use super::computed_values;
+    use servo_util::logical_geometry::WritingMode;
+
     % for style_struct in STYLE_STRUCTS:
         #[deriving(PartialEq, Clone)]
         pub struct ${style_struct.name} {
@@ -1573,6 +1587,42 @@ pub mod style_structs {
             % endfor
         }
     % endfor
+
+    impl InheritedBox {
+        /// Return a WritingMode bitflags from the relevant CSS properties.
+        pub fn get_writing_mode(&self) -> WritingMode {
+            use servo_util::logical_geometry;
+            let mut flags = WritingMode::empty();
+            match self.direction {
+                computed_values::direction::ltr => {},
+                computed_values::direction::rtl => {
+                    flags.insert(logical_geometry::FlagRTL);
+                },
+            }
+            match self.writing_mode {
+                computed_values::writing_mode::horizontal_tb => {},
+                computed_values::writing_mode::vertical_rl => {
+                    flags.insert(logical_geometry::FlagVertical);
+                },
+                computed_values::writing_mode::vertical_lr => {
+                    flags.insert(logical_geometry::FlagVertical);
+                    flags.insert(logical_geometry::FlagVerticalLR);
+                },
+            }
+            match self.text_orientation {
+                computed_values::text_orientation::sideways_right => {},
+                computed_values::text_orientation::sideways_left => {
+                    flags.insert(logical_geometry::FlagSidewaysLeft);
+                },
+                computed_values::text_orientation::sideways => {
+                    if flags.intersects(logical_geometry::FlagVerticalLR) {
+                        flags.insert(logical_geometry::FlagSidewaysLeft);
+                    }
+                },
+            }
+            flags
+        }
+    }
 }
 
 #[deriving(Clone)]
diff --git a/src/components/util/logical_geometry.rs b/src/components/util/logical_geometry.rs
new file mode 100644
index 00000000000..bd0ea74fed4
--- /dev/null
+++ b/src/components/util/logical_geometry.rs
@@ -0,0 +1,944 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+/// Geometry in flow-relative space.
+
+use geom::{Size2D, Point2D, SideOffsets2D, Rect};
+use std::fmt::{Show, Formatter, FormatError};
+use std::num::Zero;
+
+
+bitflags!(
+    flags WritingMode: u8 {
+        static FlagRTL = 1 << 0,
+        static FlagVertical = 1 << 1,
+        static FlagVerticalLR = 1 << 2,
+        static FlagSidewaysLeft = 1 << 3
+    }
+)
+
+impl WritingMode {
+    #[inline]
+    pub fn is_vertical(&self) -> bool {
+        self.intersects(FlagVertical)
+    }
+
+    /// Asuming .is_vertical(), does the block direction go left to right?
+    #[inline]
+    pub fn is_vertical_lr(&self) -> bool {
+        self.intersects(FlagVerticalLR)
+    }
+
+    /// Asuming .is_vertical(), does the inline direction go top to bottom?
+    #[inline]
+    pub fn is_inline_tb(&self) -> bool {
+        !(self.intersects(FlagSidewaysLeft) ^ self.intersects(FlagRTL))
+    }
+
+    #[inline]
+    pub fn is_bidi_ltr(&self) -> bool {
+        !self.intersects(FlagRTL)
+    }
+}
+
+impl Show for WritingMode {
+    fn fmt(&self, formatter: &mut Formatter) -> Result<(), FormatError> {
+        if self.is_vertical() {
+            try!(write!(formatter, "V"));
+            if self.is_vertical_lr() {
+                try!(write!(formatter, " LR"));
+            } else {
+                try!(write!(formatter, " RL"));
+            }
+            if self.intersects(FlagSidewaysLeft) {
+                try!(write!(formatter, " SidewaysL"));
+            }
+        } else {
+            try!(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(ndebug)]
+#[deriving(PartialEq, Eq, Clone)]
+struct DebugWritingMode;
+
+#[cfg(not(ndebug))]
+#[deriving(PartialEq, Eq, Clone)]
+struct DebugWritingMode {
+    mode: WritingMode
+}
+
+#[cfg(ndebug)]
+impl DebugWritingMode {
+    #[inline]
+    fn check(&self, _other: WritingMode) {}
+
+    #[inline]
+    fn check_debug(&self, _other: DebugWritingMode) {}
+
+    #[inline]
+    fn new(_mode: WritingMode) -> DebugWritingMode {
+        DebugWritingMode
+    }
+}
+
+#[cfg(not(ndebug))]
+impl DebugWritingMode {
+    #[inline]
+    fn check(&self, other: WritingMode) {
+        assert!(self.mode == other)
+    }
+
+    #[inline]
+    fn check_debug(&self, other: DebugWritingMode) {
+        assert!(self.mode == other.mode)
+    }
+
+    #[inline]
+    fn new(mode: WritingMode) -> DebugWritingMode {
+        DebugWritingMode { mode: mode }
+    }
+}
+
+impl Show for DebugWritingMode {
+    #[cfg(ndebug)]
+    fn fmt(&self, formatter: &mut Formatter) -> Result<(), FormatError> {
+        write!(formatter, "?")
+    }
+
+    #[cfg(not(ndebug))]
+    fn fmt(&self, formatter: &mut Formatter) -> Result<(), FormatError> {
+        self.mode.fmt(formatter)
+    }
+}
+
+
+/// A 2D size in flow-relative dimensions
+#[deriving(PartialEq, Eq, Clone)]
+pub struct LogicalSize<T> {
+    pub isize: T,  // inline-size (a.k.a. logical width)
+    pub bsize: T,  // block-size (a.k.a. logical height)
+    debug_writing_mode: DebugWritingMode,
+}
+
+impl<T: Show> Show for LogicalSize<T> {
+    fn fmt(&self, formatter: &mut Formatter) -> Result<(), FormatError> {
+        write!(formatter, "LogicalSize[{}, {}, {}]",
+               self.debug_writing_mode, self.isize, self.bsize)
+    }
+}
+
+// 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 {
+            isize: Zero::zero(),
+            bsize: Zero::zero(),
+            debug_writing_mode: DebugWritingMode::new(mode),
+        }
+    }
+
+    #[inline]
+    pub fn is_zero(&self) -> bool {
+        self.isize.is_zero() && self.bsize.is_zero()
+    }
+}
+
+impl<T: Copy> LogicalSize<T> {
+    #[inline]
+    pub fn new(mode: WritingMode, isize: T, bsize: T) -> LogicalSize<T> {
+        LogicalSize {
+            isize: isize,
+            bsize: bsize,
+            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)
+        }
+    }
+
+    #[inline]
+    pub fn width(&self, mode: WritingMode) -> T {
+        self.debug_writing_mode.check(mode);
+        if mode.is_vertical() {
+            self.bsize
+        } else {
+            self.isize
+        }
+    }
+
+    #[inline]
+    pub fn set_width(&mut self, mode: WritingMode, width: T) {
+        self.debug_writing_mode.check(mode);
+        if mode.is_vertical() {
+            self.bsize = width
+        } else {
+            self.isize = width
+        }
+    }
+
+    #[inline]
+    pub fn height(&self, mode: WritingMode) -> T {
+        self.debug_writing_mode.check(mode);
+        if mode.is_vertical() {
+            self.isize
+        } else {
+            self.bsize
+        }
+    }
+
+    #[inline]
+    pub fn set_height(&mut self, mode: WritingMode, height: T) {
+        self.debug_writing_mode.check(mode);
+        if mode.is_vertical() {
+            self.isize = height
+        } else {
+            self.bsize = height
+        }
+    }
+
+    #[inline]
+    pub fn to_physical(&self, mode: WritingMode) -> Size2D<T> {
+        self.debug_writing_mode.check(mode);
+        if mode.is_vertical() {
+            Size2D { width: self.bsize, height: self.isize }
+        } else {
+            Size2D { width: self.isize, height: self.bsize }
+        }
+    }
+
+    #[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
+        } else {
+            LogicalSize::from_physical(mode_to, self.to_physical(mode_from))
+        }
+    }
+}
+
+impl<T: Add<T, T>> Add<LogicalSize<T>, LogicalSize<T>> for 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,
+            isize: self.isize + other.isize,
+            bsize: self.bsize + other.bsize,
+        }
+    }
+}
+
+impl<T: Sub<T, T>> Sub<LogicalSize<T>, LogicalSize<T>> for 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,
+            isize: self.isize - other.isize,
+            bsize: self.bsize - other.bsize,
+        }
+    }
+}
+
+
+/// A 2D point in flow-relative dimensions
+#[deriving(PartialEq, Eq, Clone)]
+pub struct LogicalPoint<T> {
+    pub i: T,  /// inline-axis coordinate
+    pub b: T,  /// block-axis coordinate
+    debug_writing_mode: DebugWritingMode,
+}
+
+impl<T: Show> Show for LogicalPoint<T> {
+    fn fmt(&self, formatter: &mut Formatter) -> Result<(), FormatError> {
+        write!(formatter, "LogicalPoint[{}, {}, {}]",
+               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),
+        }
+    }
+
+    #[inline]
+    pub fn is_zero(&self) -> bool {
+        self.i.is_zero() && self.b.is_zero()
+    }
+}
+
+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, 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 {
+                x: if mode.is_vertical_lr() { self.b } else { container_size.width - self.b },
+                y: if mode.is_inline_tb() { self.i } else { container_size.height - self.i }
+            }
+        } else {
+            Point2D {
+                x: if mode.is_bidi_ltr() { self.i } else { container_size.width - self.i },
+                y: 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: Add<T,T>> Add<LogicalSize<T>, LogicalPoint<T>> for 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.isize,
+            b: self.b + other.bsize,
+        }
+    }
+}
+
+impl<T: Sub<T,T>> Sub<LogicalSize<T>, LogicalPoint<T>> for 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.isize,
+            b: self.b - other.bsize,
+        }
+    }
+}
+
+
+/// 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.
+#[deriving(PartialEq, Eq, Clone)]
+pub struct LogicalMargin<T> {
+    pub bstart: T,
+    pub iend: T,
+    pub bend: T,
+    pub istart: T,
+    debug_writing_mode: DebugWritingMode,
+}
+
+impl<T: Show> Show for LogicalMargin<T> {
+    fn fmt(&self, formatter: &mut Formatter) -> Result<(), FormatError> {
+        write!(formatter, "LogicalMargin[{}, bstart: {}, iend: {}, bend: {}, istart: {}]",
+               self.debug_writing_mode, self.bstart, self.iend, self.bend, self.istart)
+    }
+}
+
+impl<T: Zero> LogicalMargin<T> {
+    #[inline]
+    pub fn zero(mode: WritingMode) -> LogicalMargin<T> {
+        LogicalMargin {
+            bstart: Zero::zero(),
+            iend: Zero::zero(),
+            bend: Zero::zero(),
+            istart: Zero::zero(),
+            debug_writing_mode: DebugWritingMode::new(mode),
+        }
+    }
+
+    #[inline]
+    pub fn is_zero(&self) -> bool {
+        self.bstart.is_zero() &&
+        self.iend.is_zero() &&
+        self.bend.is_zero() &&
+        self.istart.is_zero()
+    }
+}
+
+impl<T: Copy> LogicalMargin<T> {
+    #[inline]
+    pub fn new(mode: WritingMode, bstart: T, iend: T, bend: T, istart: T) -> LogicalMargin<T> {
+        LogicalMargin {
+            bstart: bstart,
+            iend: iend,
+            bend: bend,
+            istart: istart,
+            debug_writing_mode: DebugWritingMode::new(mode),
+        }
+    }
+
+    #[inline]
+    pub fn from_physical(mode: WritingMode, offsets: SideOffsets2D<T>) -> LogicalMargin<T> {
+        let bstart;
+        let iend;
+        let bend;
+        let istart;
+        if mode.is_vertical() {
+            if mode.is_vertical_lr() {
+                bstart = offsets.left;
+                bend = offsets.right;
+            } else {
+                bstart = offsets.right;
+                bend = offsets.left;
+            }
+            if mode.is_inline_tb() {
+                istart = offsets.top;
+                iend = offsets.bottom;
+            } else {
+                istart = offsets.bottom;
+                iend = offsets.top;
+            }
+        } else {
+            bstart = offsets.top;
+            bend = offsets.bottom;
+            if mode.is_bidi_ltr() {
+                istart = offsets.left;
+                iend = offsets.right;
+            } else {
+                istart = offsets.right;
+                iend = offsets.left;
+            }
+        }
+        LogicalMargin::new(mode, bstart, iend, bend, istart)
+    }
+
+    #[inline]
+    pub fn top(&self, mode: WritingMode) -> T {
+        self.debug_writing_mode.check(mode);
+        if mode.is_vertical() {
+            if mode.is_inline_tb() { self.istart } else { self.iend }
+        } else {
+            self.bstart
+        }
+    }
+
+    #[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.istart = top } else { self.iend = top }
+        } else {
+            self.bstart = 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.bend } else { self.bstart }
+        } else {
+            if mode.is_bidi_ltr() { self.iend } else { self.istart }
+        }
+    }
+
+    #[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.bend = right } else { self.bstart = right }
+        } else {
+            if mode.is_bidi_ltr() { self.iend = right } else { self.istart = 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.iend } else { self.istart }
+        } else {
+            self.bend
+        }
+    }
+
+    #[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.iend = bottom } else { self.istart = bottom }
+        } else {
+            self.bend = 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.bstart } else { self.bend }
+        } else {
+            if mode.is_bidi_ltr() { self.istart } else { self.iend }
+        }
+    }
+
+    #[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.bstart = left } else { self.bend = left }
+        } else {
+            if mode.is_bidi_ltr() { self.istart = left } else { self.iend = 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.bstart;
+                right = self.bend;
+            } else {
+                right = self.bstart;
+                left = self.bend;
+            }
+            if mode.is_inline_tb() {
+                top = self.istart;
+                bottom = self.iend;
+            } else {
+                bottom = self.istart;
+                top = self.iend;
+            }
+        } else {
+            top = self.bstart;
+            bottom = self.bend;
+            if mode.is_bidi_ltr() {
+                left = self.istart;
+                right = self.iend;
+            } else {
+                right = self.istart;
+                left = self.iend;
+            }
+        }
+        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
+        } else {
+            LogicalMargin::from_physical(mode_to, self.to_physical(mode_from))
+        }
+    }
+}
+
+impl<T: Add<T, T>> LogicalMargin<T> {
+    #[inline]
+    pub fn istart_end(&self) -> T {
+        self.istart + self.iend
+    }
+
+    #[inline]
+    pub fn bstart_end(&self) -> T {
+        self.bstart + self.bend
+    }
+
+    #[inline]
+    pub fn top_bottom(&self, mode: WritingMode) -> T {
+        self.debug_writing_mode.check(mode);
+        if mode.is_vertical() {
+            self.istart_end()
+        } else {
+            self.bstart_end()
+        }
+    }
+
+    #[inline]
+    pub fn left_right(&self, mode: WritingMode) -> T {
+        self.debug_writing_mode.check(mode);
+        if mode.is_vertical() {
+            self.bstart_end()
+        } else {
+            self.istart_end()
+        }
+    }
+}
+
+impl<T: Add<T, T>> Add<LogicalMargin<T>, LogicalMargin<T>> for 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,
+            bstart: self.bstart + other.bstart,
+            iend: self.iend + other.iend,
+            bend: self.bend + other.bend,
+            istart: self.istart + other.istart,
+        }
+    }
+}
+
+impl<T: Sub<T, T>> Sub<LogicalMargin<T>, LogicalMargin<T>> for 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,
+            bstart: self.bstart - other.bstart,
+            iend: self.iend - other.iend,
+            bend: self.bend - other.bend,
+            istart: self.istart - other.istart,
+        }
+    }
+}
+
+
+/// A rectangle in flow-relative dimensions
+#[deriving(PartialEq, Eq, Clone)]
+pub struct LogicalRect<T> {
+    pub start: LogicalPoint<T>,
+    pub size: LogicalSize<T>,
+    debug_writing_mode: DebugWritingMode,
+}
+
+impl<T: Show> Show for LogicalRect<T> {
+    fn fmt(&self, formatter: &mut Formatter) -> Result<(), FormatError> {
+        write!(formatter, "LogicalRect[{}, istart: {}, bstart: {}, isize: {}, bsize: {}]",
+               self.debug_writing_mode, self.start.i, self.start.b,
+               self.size.isize, self.size.bsize)
+    }
+}
+
+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),
+        }
+    }
+
+    #[inline]
+    pub fn is_zero(&self) -> bool {
+        self.start.is_zero() && self.size.is_zero()
+    }
+}
+
+impl<T: Copy> LogicalRect<T> {
+    #[inline]
+    pub fn new(mode: WritingMode, istart: T, bstart: T, isize: T, bsize: T) -> LogicalRect<T> {
+        LogicalRect {
+            start: LogicalPoint::new(mode, istart, bstart),
+            size: LogicalSize::new(mode, isize, bsize),
+            debug_writing_mode: DebugWritingMode::new(mode),
+        }
+    }
+}
+
+impl<T: Copy + Add<T, T> + Sub<T, T>> LogicalRect<T> {
+    #[inline]
+    pub fn from_physical(mode: WritingMode, rect: Rect<T>, container_size: Size2D<T>)
+                         -> LogicalRect<T> {
+        let istart;
+        let bstart;
+        let isize;
+        let bsize;
+        if mode.is_vertical() {
+            isize = rect.size.height;
+            bsize = rect.size.width;
+            if mode.is_vertical_lr() {
+                bstart = rect.origin.x;
+            } else {
+                bstart = container_size.width - (rect.origin.x + rect.size.width);
+            }
+            if mode.is_inline_tb() {
+                istart = rect.origin.y;
+            } else {
+                istart = container_size.height - (rect.origin.y + rect.size.height);
+            }
+        } else {
+            isize = rect.size.width;
+            bsize = rect.size.height;
+            bstart = rect.origin.y;
+            if mode.is_bidi_ltr() {
+                istart = rect.origin.x;
+            } else {
+                istart = container_size.width - (rect.origin.x + rect.size.width);
+            }
+        }
+        LogicalRect {
+            start: LogicalPoint::new(mode, istart, bstart),
+            size: LogicalSize::new(mode, isize, bsize),
+            debug_writing_mode: DebugWritingMode::new(mode),
+        }
+    }
+
+    #[inline]
+    pub fn iend(&self) -> T {
+        self.start.i + self.size.isize
+    }
+
+    #[inline]
+    pub fn bend(&self) -> T {
+        self.start.b + self.size.bsize
+    }
+
+    #[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.bsize;
+            height = self.size.isize;
+            if mode.is_vertical_lr() {
+                x = self.start.b;
+            } else {
+                x = container_size.width - self.bend();
+            }
+            if mode.is_inline_tb() {
+                y = self.start.i;
+            } else {
+                y = container_size.height - self.iend();
+            }
+        } else {
+            width = self.size.isize;
+            height = self.size.bsize;
+            y = self.start.b;
+            if mode.is_bidi_ltr() {
+                x = self.start.i;
+            } else {
+                x = container_size.width - self.iend();
+            }
+        }
+        Rect {
+            origin: Point2D { x: x, y: y },
+            size: Size2D { width: width, height: 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)
+        }
+    }
+}
+
+impl<T: Add<T, T> + Sub<T, T>> Add<LogicalMargin<T>, LogicalRect<T>> for 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.istart,
+                b: self.start.b - other.bstart,
+                debug_writing_mode: self.debug_writing_mode,
+            },
+            size: LogicalSize {
+                isize: self.size.isize + other.istart_end(),
+                bsize: self.size.bsize + other.bstart_end(),
+                debug_writing_mode: self.debug_writing_mode,
+            },
+            debug_writing_mode: self.debug_writing_mode,
+        }
+    }
+}
+
+
+impl<T: Add<T, T> + Sub<T, T>> Sub<LogicalMargin<T>, LogicalRect<T>> for 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.istart,
+                b: self.start.b + other.bstart,
+                debug_writing_mode: self.debug_writing_mode,
+            },
+            size: LogicalSize {
+                isize: self.size.isize - other.istart_end(),
+                bsize: self.size.bsize - other.bstart_end(),
+                debug_writing_mode: self.debug_writing_mode,
+            },
+            debug_writing_mode: self.debug_writing_mode,
+        }
+    }
+}
+
+#[cfg(test)]
+fn modes() -> [WritingMode, ..10] {
+    [
+        WritingMode::empty(),
+        FlagVertical,
+        FlagVertical | FlagVerticalLR,
+        FlagVertical | FlagVerticalLR | FlagSidewaysLeft,
+        FlagVertical | FlagSidewaysLeft,
+        FlagRTL,
+        FlagVertical | FlagRTL,
+        FlagVertical | FlagVerticalLR | FlagRTL,
+        FlagVertical | FlagVerticalLR | FlagSidewaysLeft | FlagRTL,
+        FlagVertical | FlagSidewaysLeft | FlagRTL,
+    ]
+}
+
+#[test]
+fn test_size_round_trip() {
+    let physical = Size2D(1, 2);
+    for &mode in modes().iter() {
+        let logical = LogicalSize::from_physical(mode, physical);
+        assert!(logical.to_physical(mode) == physical);
+        assert!(logical.width(mode) == 1);
+        assert!(logical.height(mode) == 2);
+    }
+}
+
+#[test]
+fn test_point_round_trip() {
+    let physical = Point2D(1, 2);
+    let container = Size2D(100, 200);
+    for &mode in modes().iter() {
+        let logical = LogicalPoint::from_physical(mode, physical, container);
+        assert!(logical.to_physical(mode, container) == physical);
+        assert!(logical.x(mode, container) == 1);
+        assert!(logical.y(mode, container) == 2);
+    }
+}
+
+#[test]
+fn test_margin_round_trip() {
+    let physical = SideOffsets2D::new(1, 2, 3, 4);
+    for &mode in modes().iter() {
+        let logical = LogicalMargin::from_physical(mode, physical);
+        assert!(logical.to_physical(mode) == physical);
+        assert!(logical.top(mode) == 1);
+        assert!(logical.right(mode) == 2);
+        assert!(logical.bottom(mode) == 3);
+        assert!(logical.left(mode) == 4);
+    }
+}
+
+#[test]
+fn test_rect_round_trip() {
+    let physical = Rect(Point2D(1, 2), Size2D(3, 4));
+    let container = Size2D(100, 200);
+    for &mode in modes().iter() {
+        let logical = LogicalRect::from_physical(mode, physical, container);
+        assert!(logical.to_physical(mode, container) == physical);
+    }
+}
diff --git a/src/components/util/util.rs b/src/components/util/util.rs
index 31f0b2295c9..1f60ce6c0d6 100644
--- a/src/components/util/util.rs
+++ b/src/components/util/util.rs
@@ -32,6 +32,7 @@ extern crate std_url = "url";
 pub mod cache;
 pub mod debug_utils;
 pub mod geometry;
+pub mod logical_geometry;
 pub mod memory;
 pub mod namespace;
 pub mod opts;