Module cache 

Core types and layout pipeline for the text/inline formatting context.

This module defines the central data structures (UnifiedConstraints, LayoutCache, FontManager, UnifiedLayout, etc.) and implements the 5-stage inline layout pipeline:

1. Logical Analysis — InlineContent → LogicalItem
2. BiDi Reordering — LogicalItem → VisualItem
3. Shaping — VisualItem → ShapedItem
4. Text Orientation — vertical writing-mode transforms
5. Flow / Positioning — line breaking + final PositionedItem placement

The module also contains cursor movement helpers, caching infrastructure (per-item and monolithic), and font management (FontContext, FontManager, LoadedFonts). Integration with the box layout solver lives in solver3/fc.rs.

Re-exports

pub use crate::font_traits::ParsedFontTrait;

pub use crate::font_traits::ShallowClone;

Structs

BidiLevel

BreakCursor

CachedLineBreaks

Cached line break boundaries from a previous layout pass. Enables incremental relayout: when a word changes width, we can check if it still fits on the same line without re-running the full line-breaking algorithm.

ContentIndex

A stable, logical pointer to an item within the original InlineContent array.

CursorBoundsError

Error returned when cursor movement hits a boundary

FlowLayout

Represents the final layout distributed across multiple fragments.

FontChainKey

Key for caching font chains - based only on CSS properties, not text content

FontContext

Bundles all font-related state that can be shared across layout passes.

FontHash

A reference to a font for rendering, identified by its hash. This hash corresponds to ParsedFont::hash and is used to look up the actual font data in the renderer’s font cache.

FontManager

FontSelector

A selector for loading fonts from the font cache. Used by FontManager to query fontconfig and load font files.

Glyph

Enhanced glyph with all features

GraphemeClusterId

A stable, logical identifier for a grapheme cluster.

HyphenationBreak

Represents a single valid hyphenation point within a word.

InitialLetter

InlineBorderInfo

Border information for inline elements (display: inline, inline-block)

InlineBreak

InlineImage

InlineShape

InlineSpace

IntrinsicTextSizes

Inline-axis intrinsic contributions derived from shaped text, without running the line-breaking stage of the pipeline.

LayoutFontMetrics

Layout-specific font metrics extracted from FontMetrics Contains only the metrics needed for text layout and rendering

LayoutFragment

Defines a single area for layout, with its own shape and properties.

LayoutKey

Key for the final layout stage.

LineConstraints

Line constraints with multi-segment support

LineSegment

LoadedFonts

A map of pre-loaded fonts, keyed by FontId (from rust-fontconfig)

LogicalItemsKey

Key for caching the conversion from InlineContent to LogicalItems.

MeasuredImage

MeasuredShape

OverflowInfo

Stores information about content that exceeded the available layout space.

PartialStyleProperties

PerItemShapedEntry

Cached shaped result for a single visual item (or coalesced group). Enables per-item cache hits when only one word changes in a paragraph.

Point

PositionedItem

Rect

ShapeConstraints

ShapedCluster

A group of glyphs that corresponds to one or more source characters (a cluster).

ShapedGlyph

A single, shaped glyph with its essential metrics.

ShapedItemsKey

Key for caching the shaping stage.

Size

Stroke

StyleOverride

StyleProperties

Style properties with vertical text support

StyledRun

TextCacheMemoryReport

Approximate heap bytes retained by a TextShapingCache.

TextDecoration

TextRunInfo

TextShapingCache

UnifiedConstraints

Unified constraints combining all layout features

UnifiedLayout

UnifiedLine

Intermediate structure carrying information from the line breaker to the positioner.

VerticalMetrics

VisualItem

VisualItemsKey

Key for caching the Bidi reordering stage.

VisualRun

Enums

AvailableSpace

Available space for layout, similar to Taffy’s AvailableSpace.

BidiDirection

BreakType

CharacterClass

ClearType

FontChainKeyOrRef

Either a FontChainKey (resolved via fontconfig) or a direct FontRef hash.

FontOrRef

Enum that wraps either a fontconfig-resolved font (T) or a direct FontRef.

FontStack

Font stack that can be either a list of font selectors (resolved via fontconfig) or a direct FontRef (bypasses fontconfig entirely).

FontStyle

FontVariantCaps

FontVariantEastAsian

FontVariantLigatures

FontVariantNumeric

GlyphKind

The kind of a glyph, used to distinguish characters from layout-inserted items.

GlyphOrientation

GlyphSource

Hyphens

Controls whether hyphenation is allowed to create soft wrap opportunities.

ImageSource

IncrementalRelayoutResult

Result of an incremental relayout attempt.

InitialLetterAlign

Alignment mode for initial letters, controlling which alignment points are used to size and position the letter relative to the root inline box.

InlineContent

JustifyContent

LayoutError

LineBreakStrictness

LineHeight

CSS line-height value.

LogicalItem

ObjectFit

OverflowBehavior

OverflowWrap

CSS overflow-wrap (aka word-wrap) property.

PathSegment

SegmentAlignment

Defines how text should be aligned when a line contains multiple disjoint segments.

ShapeBoundary

ShapeDefinition

ShapedItem

Spacing

TextAlign

TextBoundary

Text boundary types for cursor movement

TextCombineUpright

TextOrientation

TextTransform

TextWrap

UnicodeBidi

CSS unicode-bidi property values relevant to layout. When Plaintext, the bidi algorithm uses P2/P3 heuristics to auto-detect paragraph direction from text content, instead of the HL1 override from the CSS direction property.

VerticalAlign

WhiteSpaceMode

WordBreak

WritingMode

Functions

break_one_line

Breaks a single line of items to fit within the given geometric constraints, handling multi-segment lines and hyphenation. Break a single line from the current cursor position.

create_logical_items

extract_line_breaks

Extract line break boundaries from a positioned items list.

find_all_hyphenation_breaks

A “word” is defined as a sequence of one or more adjacent ShapedClusters.

get_base_direction_from_logical

get_item_measure

Helper to get the primary measure (width or height) of a shaped item.

get_item_vertical_metrics

Gets the ascent (distance from baseline to top) and descent (distance from baseline to bottom) for a single item, incorporating half-leading from line-height. +spec:display-property:fd42a9 - line-height affects line box contribution, not inline box size

get_item_vertical_metrics_approx

Approximate version of get_item_vertical_metrics for use without constraints (e.g. bounds()). Uses 80/20 ascent/descent ratio as fallback for empty-glyph strut case.

is_collapsible_whitespace

Returns true if the item is collapsible whitespace per CSS Text 3 §4.1.2 Phase II. This is used for stripping leading/trailing whitespace at line edges — distinct from is_word_separator which is for word-spacing per §7.1.

is_cursive_script_cluster

Returns true if the cluster’s first character belongs to a cursive script (Arabic, Syriac, Mongolian, N’Ko, Mandaic, Phags Pa, Hanifi Rohingya) per CSS Text 3 Appendix D. These scripts should not have letter-spacing applied.

is_word_separator

is_zero_width_space

Helper to identify if an item is a zero-width space (U+200B), which provides a soft wrap opportunity with no visible width. Used in scripts like Thai, Lao, and Khmer that don’t use spaces between words.

justify_kashida_and_rebuild

Rebuilds a line of items, inserting Kashida glyphs for justification.

perform_fragment_layout

Performs layout for a single fragment, consuming items from a BreakCursor.

position_one_line

Positions a single line of items, handling alignment and justification within segments.

reorder_logical_items

shape_visual_items

shape_visual_items_with_per_item_cache

Shape visual items into ShapedItems using pre-loaded fonts.

try_incremental_relayout

Attempt incremental relayout given old metrics and new per-item advance widths.

Type Aliases

CacheId

FourCc

ShapedGlyphVec

Glyph storage for a single shaped cluster. Inline one glyph (the common case for Latin text), spill to heap for ligatures / combining marks / multi-glyph clusters. The union feature of smallvec packs the inline buffer and the heap pointer into the same bytes, so sizeof stays sizeof(ShapedGlyph) + 2*usize regardless of inline/heap state.