Phase 4: layout writing modes

CHANGELOG.md

@@ -125,6 +125,67 @@ tagged release.
   time.
 - `GridLine::Area` uses `String` for area names. Spec used `SmolStr`;
   Phase 3 uses `String` to avoid a new direct supply-chain dep.
+- **Layout writing modes (Phase 4 of the layout migration).**
+  - `WritingMode` component (joins `Style`'s Bundle): `mode`,
+    `direction`, `text_orientation`, `unicode_bidi`. CSS-faithful surface
+    for writing-mode + direction + text-orientation + unicode-bidi.
+  - `WritingModeResolved` private cache component, populated by the new
+    `BuiyLayoutStep::WritingModeInherit` pipeline step. Memoized
+    multi-level ancestor walk; idempotent insert preserves Phase 1's
+    O(0) steady-state contract.
+  - 4 supporting enums: `WritingModeKind` (HorizontalTb / VerticalRl /
+    VerticalLr / SidewaysRl / SidewaysLr), `Direction` (Ltr / Rtl),
+    `TextOrientation` (Mixed / Upright / Sideways), `UnicodeBidi`
+    (Normal / Embed / Isolate / BidiOverride / IsolateOverride / Plaintext).
+  - `LogicalEdges` value type with `to_edges(WritingModeKind, Direction)`.
+  - `LogicalBoxModel` and `LogicalInset` author-ergonomic builder
+    structs (non-component, non-Bundle) with `.to_box_model(&WritingMode)`
+    and `.to_inset(&WritingMode)` methods. Vertical modes swap inline ↔
+    block onto width ↔ height.
+  - 7 fluent setters on `Style`: `.writing_mode(_)`,
+    `.writing_mode_kind(_)`, `.direction(_)`, `.ltr()`, `.rtl()`,
+    `.text_orientation(_)`, `.unicode_bidi(_)`.
+  - `WritingMode` + `WritingModeResolved` + 5 value types registered
+    for reflection in `LayoutPlugin`.
+  - New `BuiyLayoutStep::WritingModeInherit` pipeline step inserted
+    between `RemovedNodesGc` and `SyncStyles`. The 8-step layout chain
+    becomes 9. `tests/layout_pipeline_order.rs` widens to assert all 9.
+  - `Direction::Rtl` flows through `taffy::Style.direction`, mirroring
+    flex children under RTL.
+  - `WritingModeKind::Sideways{Rl,Lr}` emit one `warn!` per session and
+    fall back to their non-sideways vertical equivalent for layout
+    purposes. Glyph rotation is `buiy-text-rendering-design`'s concern.
+
+### Changed (Phase 4)
+- `inherit_writing_mode`'s ancestor walk treats `WritingMode::default()`
+  as "unset" (CSS `initial`-like). Without this, every `Style`-spawned
+  entity's bundled `WritingMode::default()` would short-circuit the
+  walk so descendants of a non-default ancestor would resolve to
+  default instead of inheriting. Trade-off: an author cannot explicitly
+  pin `WritingMode::default()` as an override against a non-default
+  ancestor; the result is observationally identical to inheriting the
+  root default.
+- `sync_styles`'s `Or<>` trigger filter widens with `Changed<WritingMode>`
+  and `Changed<WritingModeResolved>`. **Phase 2 invariant intact:**
+  `Changed<ScrollOffset>` / `Changed<ScrollSnapItem>` remain excluded.
+- Pipeline gains a 9th step (`WritingModeInherit`); the layout chain
+  is now 0 → wmi → 1 → ... → 7 in declared order.
+
+### Deferred (Phase 4)
+- `ContainingBlock` cache — deferred to Phase 6 (anchor positioning)
+  where it has a real consumer.
+- Dynamic writing-mode switches (CSS `Changed<WritingMode>` →
+  re-translation pass) — Phase 4 v1 ships construct-time-only
+  `LogicalBoxModel` / `LogicalInset` translation; runtime flips
+  require re-spawn / re-insert. Re-translation pass is a v1.x feature
+  contingent on resolving spec § 4.1 vs § 4.2 internal inconsistency.
+- Vertical-mode Taffy axis-swap — Taffy 0.10 has no writing-mode
+  awareness. Vertical modes are honored only by the logical builders;
+  Taffy still flows the main axis horizontally. Authors who want
+  top-to-bottom flow under vertical-rl use `Display::Flex(Column)`.
+- Sideways glyph rotation — owned by `buiy-text-rendering-design`.
+- BiDi resolution algorithm for `unicode_bidi` — owned by
+  `buiy-i18n-design`. Phase 4 stores the value only.
 
 ### Removed
 - `buiy_core::components::Style` (the Phase 0 mega-component) and

crates/buiy/src/lib.rs

@@ -10,12 +10,14 @@ pub use buiy_core::{
     components::{Node, ResolvedLayout, Visual},
     focus::{FocusVisible, Focusable, FocusedEntity},
     layout::{
-        AlignContent, AlignItems, AspectRatio, BoxModel, BoxSizing, BuiyLayoutStep, Display, Edges,
-        FlexAxis, FlexGap, FlexItem, FlexParams, FlexWrap, GridAreas, GridAutoFlow, GridItem,
-        GridLine, GridParams, Inset, JustifyContent, JustifyItems, LayoutPlugin, Length, NamedArea,
-        Overflow, OverflowMode, OverscrollBehavior, Position, PositionKind, RepeatCount, Scroll,
-        ScrollBehavior, ScrollOffset, ScrollSnapItem, ScrollbarColor, ScrollbarGutter,
-        ScrollbarWidth, Sizing, SnapAlign, SnapStop, SnapType, Style, TrackSize,
+        AlignContent, AlignItems, AspectRatio, BoxModel, BoxSizing, BuiyLayoutStep, Direction,
+        Display, Edges, FlexAxis, FlexGap, FlexItem, FlexParams, FlexWrap, GridAreas, GridAutoFlow,
+        GridItem, GridLine, GridParams, Inset, JustifyContent, JustifyItems, LayoutPlugin, Length,
+        LogicalBoxModel, LogicalEdges, LogicalInset, NamedArea, Overflow, OverflowMode,
+        OverscrollBehavior, Position, PositionKind, RepeatCount, Scroll, ScrollBehavior,
+        ScrollOffset, ScrollSnapItem, ScrollbarColor, ScrollbarGutter, ScrollbarWidth, Sizing,
+        SnapAlign, SnapStop, SnapType, Style, TextOrientation, TrackSize, UnicodeBidi, WritingMode,
+        WritingModeKind, WritingModeResolved,
     },
     picking::{BuiyPickingBackendPlugin, Hovered},
     theme::{Theme, UserPreferences, default_light_theme},

crates/buiy_core/src/layout/components.rs

@@ -11,10 +11,11 @@
 //! respective phase plans (see foundation plan §"Phasing strategy").
 
 use super::types::{
-    AlignContent, AlignItems, AspectRatio, BoxSizing, Edges, FlexAxis, FlexGap, FlexWrap,
-    GridAreas, GridAutoFlow, GridLine, Inset, JustifyContent, JustifyItems, OverflowMode,
+    AlignContent, AlignItems, AspectRatio, BoxSizing, Direction, Edges, FlexAxis, FlexGap,
+    FlexWrap, GridAreas, GridAutoFlow, GridLine, Inset, JustifyContent, JustifyItems, OverflowMode,
     OverscrollBehavior, PositionKind, ScrollBehavior, ScrollbarColor, ScrollbarGutter,
-    ScrollbarWidth, Sizing, SnapAlign, SnapStop, SnapType, TrackSize,
+    ScrollbarWidth, Sizing, SnapAlign, SnapStop, SnapType, TextOrientation, TrackSize, UnicodeBidi,
+    WritingModeKind,
 };
 use bevy::prelude::*;
 
@@ -233,6 +234,62 @@ pub struct GridItem {
     pub align_self: Option<AlignItems>,
 }
 
+/// CSS writing-mode + direction + text-orientation + unicode-bidi, all on
+/// one component because they're authored together. Joins `Style`'s
+/// Bundle. The inherited effective value is computed by the
+/// `inherit_writing_mode` system and stored in `WritingModeResolved`.
+///
+/// Spec: docs/specs/2026-05-08-buiy-layout-design/container-queries-and-writing-modes.md § 2.1.
+///
+/// Note: vertical writing-modes (`VerticalRl` / `VerticalLr`) do *not*
+/// reorient the Taffy main axis — Taffy 0.10 has no writing-mode
+/// awareness at the layout-engine level. Vertical modes are honored only
+/// by the `LogicalBoxModel` / `LogicalInset` ergonomic builders. Authors
+/// who want top-to-bottom flow under vertical-rl use
+/// `Display::Flex(Column)` explicitly. See plan § Decisions made #5.
+#[derive(Component, Reflect, Default, Clone, Copy, Debug, PartialEq, Eq)]
+#[reflect(Component, Default)]
+pub struct WritingMode {
+    pub mode: WritingModeKind,
+    pub direction: Direction,
+    pub text_orientation: TextOrientation,
+    pub unicode_bidi: UnicodeBidi,
+}
+
+/// Inherited effective writing-mode for an entity. Synced by the
+/// `inherit_writing_mode` system in `BuiyLayoutStep::WritingModeInherit`,
+/// run before `SyncStyles`. **Private cache — not author-set, not in
+/// `Style`'s Bundle.**
+///
+/// The translation layer (`style_to_taffy`) reads this value to wire
+/// `Direction::Rtl` to `taffy::Style.direction` and to gate `Sideways{Rl,Lr}`
+/// through the warn-once fallback. The `LogicalBoxModel` and `LogicalInset`
+/// builders take a `&WritingMode` directly (not the Resolved cache),
+/// because they translate at construct time on the author's side.
+///
+/// Spec: docs/specs/2026-05-08-buiy-layout-design/container-queries-and-writing-modes.md § 2.2.
+#[derive(Component, Reflect, Default, Clone, Copy, Debug, PartialEq, Eq)]
+#[reflect(Component, Default)]
+pub struct WritingModeResolved {
+    pub mode: WritingModeKind,
+    pub direction: Direction,
+    pub text_orientation: TextOrientation,
+    pub unicode_bidi: UnicodeBidi,
+}
+
+impl WritingModeResolved {
+    /// Construct from a parent `WritingMode`. Used by the inheritance
+    /// system to copy fields one-to-one.
+    pub(crate) fn from_writing_mode(wm: &WritingMode) -> Self {
+        Self {
+            mode: wm.mode,
+            direction: wm.direction,
+            text_orientation: wm.text_orientation,
+            unicode_bidi: wm.unicode_bidi,
+        }
+    }
+}
+
 /// Runtime scroll position of a scroll container. Mutated by the
 /// scroll-input handler in `buiy-input-events-design`. Read by render
 /// (drawing) and picking (hit-testing) at consume time, and by Phase 7
@@ -414,4 +471,22 @@ mod tests {
         assert_eq!(g.justify_self, None);
         assert_eq!(g.align_self, None);
     }
+
+    #[test]
+    fn writing_mode_default_is_horizontal_tb_ltr_mixed_normal() {
+        let wm = WritingMode::default();
+        assert_eq!(wm.mode, WritingModeKind::HorizontalTb);
+        assert_eq!(wm.direction, Direction::Ltr);
+        assert_eq!(wm.text_orientation, TextOrientation::Mixed);
+        assert_eq!(wm.unicode_bidi, UnicodeBidi::Normal);
+    }
+
+    #[test]
+    fn writing_mode_resolved_default_is_horizontal_tb_ltr_mixed_normal() {
+        let wm = WritingModeResolved::default();
+        assert_eq!(wm.mode, WritingModeKind::HorizontalTb);
+        assert_eq!(wm.direction, Direction::Ltr);
+        assert_eq!(wm.text_orientation, TextOrientation::Mixed);
+        assert_eq!(wm.unicode_bidi, UnicodeBidi::Normal);
+    }
 }

crates/buiy_core/src/layout/mod.rs

@@ -12,16 +12,17 @@ mod types;
 
 pub use components::{
     BoxModel, Display, FlexItem, FlexParams, GridItem, GridParams, Overflow, Position, Scroll,
-    ScrollOffset, ScrollSnapItem,
+    ScrollOffset, ScrollSnapItem, WritingMode, WritingModeResolved,
 };
 pub use pipeline::BuiyLayoutStep;
-pub use style::Style;
+pub use style::{LogicalBoxModel, LogicalInset, Style};
 pub use tree::LayoutTree;
 pub use types::{
-    AlignContent, AlignItems, AspectRatio, BoxSizing, Edges, FlexAxis, FlexGap, FlexWrap,
-    GridAreas, GridAutoFlow, GridLine, Inset, JustifyContent, JustifyItems, Length, NamedArea,
-    OverflowMode, OverscrollBehavior, PositionKind, RepeatCount, ScrollBehavior, ScrollbarColor,
-    ScrollbarGutter, ScrollbarWidth, Sizing, SnapAlign, SnapStop, SnapType, TrackSize,
+    AlignContent, AlignItems, AspectRatio, BoxSizing, Direction, Edges, FlexAxis, FlexGap,
+    FlexWrap, GridAreas, GridAutoFlow, GridLine, Inset, JustifyContent, JustifyItems, Length,
+    LogicalEdges, NamedArea, OverflowMode, OverscrollBehavior, PositionKind, RepeatCount,
+    ScrollBehavior, ScrollbarColor, ScrollbarGutter, ScrollbarWidth, Sizing, SnapAlign, SnapStop,
+    SnapType, TextOrientation, TrackSize, UnicodeBidi, WritingModeKind,
 };
 
 use bevy::prelude::*;
@@ -44,6 +45,8 @@ impl Plugin for LayoutPlugin {
             .register_type::<ScrollSnapItem>()
             .register_type::<GridParams>()
             .register_type::<GridItem>()
+            .register_type::<WritingMode>()
+            .register_type::<WritingModeResolved>()
             .register_type::<Edges>()
             .register_type::<Sizing>()
             .register_type::<Length>()
@@ -55,14 +58,20 @@ impl Plugin for LayoutPlugin {
             .register_type::<GridAreas>()
             .register_type::<NamedArea>()
             .register_type::<GridAutoFlow>()
-            .register_type::<JustifyItems>();
+            .register_type::<JustifyItems>()
+            .register_type::<WritingModeKind>()
+            .register_type::<Direction>()
+            .register_type::<TextOrientation>()
+            .register_type::<UnicodeBidi>()
+            .register_type::<LogicalEdges>();
 
         pipeline::configure_pipeline(app);
 
         app.add_systems(
             Update,
             (
                 systems::gc_removed_nodes.in_set(BuiyLayoutStep::RemovedNodesGc),
+                systems::inherit_writing_mode.in_set(BuiyLayoutStep::WritingModeInherit),
                 systems::sync_styles.in_set(BuiyLayoutStep::SyncStyles),
                 systems::taffy_compute.in_set(BuiyLayoutStep::TaffyCompute),
                 systems::write_resolved_layout.in_set(BuiyLayoutStep::WriteResolvedLayout),

crates/buiy_core/src/layout/pipeline.rs

@@ -2,10 +2,12 @@
 //!
 //! Spec: docs/specs/2026-05-08-buiy-layout-design/architecture.md § 3.
 //!
-//! Eight ordered sub-sets of `BuiySet::Layout`. Phase 1 wires all eight;
-//! steps 2 (`CqActivate`), 4 (`CqFlipCheck`), 5 (`CqFlipReRun`), and 6
-//! (`PostTaffyOverrides`) are no-ops in Phase 1. Later phases attach
-//! systems to those sub-sets without reordering.
+//! Nine ordered sub-sets of `BuiySet::Layout`. Phase 1 wires the original
+//! eight; Phase 4 inserts `WritingModeInherit` between `RemovedNodesGc`
+//! and `SyncStyles` so step 1 sees the effective inherited writing-mode
+//! for every entity. Steps 2 (`CqActivate`), 4 (`CqFlipCheck`), 5
+//! (`CqFlipReRun`), and 6 (`PostTaffyOverrides`) remain no-ops in Phase 1.
+//! Later phases attach systems to those sub-sets without reordering.
 
 use bevy::prelude::*;
 
@@ -15,6 +17,11 @@ use bevy::prelude::*;
 pub enum BuiyLayoutStep {
     /// Step 0 — drop despawned entities from `LayoutTree`.
     RemovedNodesGc,
+    /// Pre-step-1 — populate `WritingModeResolved` by walking the
+    /// hierarchy. Runs before `SyncStyles` so step 1 sees the effective
+    /// inherited writing-mode for every entity.
+    /// **Phase 4.**
+    WritingModeInherit,
     /// Step 1 — translate changed Buiy components → `taffy::Style` and
     /// sync hierarchy.
     SyncStyles,
@@ -36,12 +43,13 @@ pub enum BuiyLayoutStep {
     WriteResolvedLayout,
 }
 
-/// Configure the 8-step chain inside `BuiySet::Layout`.
+/// Configure the 9-step chain inside `BuiySet::Layout`.
 pub fn configure_pipeline(app: &mut App) {
     app.configure_sets(
         Update,
         (
             BuiyLayoutStep::RemovedNodesGc,
+            BuiyLayoutStep::WritingModeInherit,
             BuiyLayoutStep::SyncStyles,
             BuiyLayoutStep::CqActivate,
             BuiyLayoutStep::TaffyCompute,