Struct TextShapingCache 

pub struct TextShapingCache { /* private fields */ }

Implementations

impl TextShapingCache

pub fn new() -> Self

pub fn memory_report(&self) -> TextCacheMemoryReport

Approximate per-stage heap-byte breakdown.

pub fn begin_generation(&mut self)

Call at the start of each layout pass. Evicts per-item shaped entries not accessed in the previous generation to prevent unbounded growth.

pub fn use_old_layout( old_constraints: &UnifiedConstraints, new_constraints: &UnifiedConstraints, old_content: &[InlineContent], new_content: &[InlineContent], ) -> bool

Check if we can reuse an old layout based on layout-affecting parameters.

This function compares only the parameters that affect glyph positions, not rendering-only parameters like color or text-decoration.

Parameters

• old_constraints: The constraints used for the cached layout
• new_constraints: The constraints for the new layout request
• old_content: The content used for the cached layout
• new_content: The new content to layout

Returns

• true if the old layout can be reused (only rendering changed)
• false if a new layout is needed (layout-affecting params changed)

impl TextShapingCache

pub fn layout_flow<T: ParsedFontTrait>( &mut self, content: &[InlineContent], style_overrides: &[StyleOverride], flow_chain: &[LayoutFragment], font_chain_cache: &HashMap<FontChainKey, FontFallbackChain>, fc_cache: &FcFontCache, loaded_fonts: &LoadedFonts<T>, debug_messages: &mut Option<Vec<LayoutDebugMessage>>, ) -> Result<FlowLayout, LayoutError>

New top-level entry point for flowing layout across multiple regions.

This function orchestrates the entire layout pipeline, but instead of fitting content into a single set of constraints, it flows the content through an ordered sequence of LayoutFragments.

CSS Inline Layout Module Level 3: Pipeline Implementation

This implements the inline formatting context with 5 stages:

Stage 1: Logical Analysis (InlineContent -> LogicalItem)

\u2705 IMPLEMENTED: Parses raw content into logical units

• Handles text runs, inline-blocks, replaced elements
• Applies style overrides at character level
• Implements \u00a7 2.2: Content size contribution calculation

Stage 2: BiDi Reordering (LogicalItem -> VisualItem)

\u2705 IMPLEMENTED: Uses CSS ‘direction’ property per CSS Writing Modes

• Reorders items for right-to-left text (Arabic, Hebrew)
• Respects containing block direction (not auto-detection)
• Conforms to Unicode BiDi Algorithm (UAX #9)

Stage 3: Shaping (VisualItem -> ShapedItem)

\u2705 IMPLEMENTED: Converts text to glyphs

• Uses HarfBuzz for OpenType shaping
• Handles ligatures, kerning, contextual forms
• Caches shaped results for performance

Stage 4: Text Orientation Transformations

\u26a0\ufe0f PARTIAL: Applies text-orientation for vertical text

• Uses constraints from first fragment only
• \u274c TODO: Should re-orient if fragments have different writing modes

Stage 5: Flow Loop (ShapedItem -> PositionedItem)

\u2705 IMPLEMENTED: Breaks lines and positions content

• Calls perform_fragment_layout for each fragment
• Uses BreakCursor to flow content across fragments
• Implements \u00a7 5: Line breaking and hyphenation

Missing Features from CSS Inline-3:

• \u00a7 3.3: initial-letter (drop caps)
• \u00a7 4: vertical-align (only baseline supported)
• \u00a7 6: text-box-trim (leading trim)
• \u00a7 7: inline-sizing (aspect-ratio for inline-blocks)

Arguments

• content - The raw InlineContent to be laid out.
• style_overrides - Character-level style changes.
• flow_chain - An ordered slice of LayoutFragment defining the regions (e.g., columns, pages) that the content should flow through.
• font_chain_cache - Pre-resolved font chains (from FontManager.font_chain_cache)
• fc_cache - The fontconfig cache for font lookups
• loaded_fonts - Pre-loaded fonts, keyed by FontId

Returns

A FlowLayout struct containing the positioned items for each fragment that was filled, and any content that did not fit in the final fragment.

pub fn measure_intrinsic_widths<T: ParsedFontTrait>( &mut self, content: &[InlineContent], style_overrides: &[StyleOverride], constraints: &UnifiedConstraints, font_chain_cache: &HashMap<FontChainKey, FontFallbackChain>, fc_cache: &FcFontCache, loaded_fonts: &LoadedFonts<T>, debug_messages: &mut Option<Vec<LayoutDebugMessage>>, ) -> Result<IntrinsicTextSizes, LayoutError>

Runs stages 1–4 of the layout pipeline (logical analysis, BiDi, shaping, text orientation) and derives min/max-content widths by scanning the resulting ShapedItems directly — without running stage 5’s line-breaking BreakCursor loop.

Used by calculate_ifc_root_intrinsic_sizes to avoid the 24% CPU spent cloning ShapedClusters inside BreakCursor::peek_next_unit on every sizing pass. Since stages 1–3 hit the same per_item_shaped cache as layout_flow, a subsequent layout_flow call for the same content at a real container width is a pure cache hit for the shaping work.

The item walk uses the same break-opportunity predicate that the BreakCursor would — min-content accumulates advances between break opportunities and tracks the maximum; max-content is the sum of all advances (as if the flow were laid out on a single infinitely-wide line).

Trait Implementations

impl Default for TextShapingCache

fn default() -> Self

Returns the “default value” for a type.