Struct LayoutNode 

#[repr(C)]
pub struct LayoutNode {

    pub box_props: BoxProps,
    pub dom_node_id: Option<NodeId>,
    pub children: Vec<usize>,
    pub used_size: Option<LogicalSize>,
    pub formatting_context: FormattingContext,
    pub parent: Option<usize>,
    pub intrinsic_sizes: Option<IntrinsicSizes>,
    pub baseline: Option<f32>,
    pub inline_layout_result: Option<CachedInlineLayout>,
    pub scrollbar_info: Option<ScrollbarRequirements>,
    pub relative_position: Option<LogicalPosition>,
    pub overflow_content_size: Option<LogicalSize>,
    pub taffy_cache: Cache,
    pub computed_style: ComputedLayoutStyle,
    pub pseudo_element: Option<PseudoElement>,
    pub escaped_top_margin: Option<f32>,
    pub escaped_bottom_margin: Option<f32>,
    pub parent_formatting_context: Option<FormattingContext>,
    pub ifc_membership: Option<IfcMembership>,
    pub containing_block_index: Option<usize>,
    pub anonymous_type: Option<AnonymousBoxType>,
    pub node_data_fingerprint: NodeDataFingerprint,
    pub subtree_hash: SubtreeHash,
    pub dirty_flag: DirtyFlag,
    pub unresolved_box_props: UnresolvedBoxProps,
    pub ifc_id: Option<IfcId>,
}

A layout tree node representing the CSS box model.

Memory Layout Optimization (#[repr(C)])

Fields are ordered by access frequency (hottest first) to maximize CPU cache line utilization during tree traversal. With #[repr(C)], the compiler preserves this ordering. The 6 hottest fields (~140 bytes) occupy the first 2-3 cache lines (64 bytes each), which are loaded first by the hardware prefetcher.

Tier	Fields	~Bytes	Accesses
HOT	box_props, dom_node_id, children,	~140	410+
	used_size, formatting_context, parent
WARM	intrinsic_sizes..computed_style	~220	~80
COLD	dirty_flag..is_anonymous	~190	~20

Note: An absolute position is a final paint-time value and shouldn’t be cached on the node itself, as it can change even if the node’s layout is clean (e.g., if a sibling changes size). We will calculate it in a separate map.

Fields

box_props: BoxProps

The resolved box model properties (margin, border, padding) in logical pixels. Cached after first resolution. (148 accesses — hottest field)

dom_node_id: Option<NodeId>

Reference back to the original DOM node (None for anonymous boxes) (111 accesses)

children: Vec<usize>

Children indices in the layout tree (53 accesses)

used_size: Option<LogicalSize>

The size used during the last layout pass. (43 accesses)

formatting_context: FormattingContext

The formatting context this node establishes or participates in. (30 accesses)

parent: Option<usize>

Parent index (None for root) (25 accesses)

intrinsic_sizes: Option<IntrinsicSizes>

Cached intrinsic sizes (min-content, max-content, etc.) (16 accesses — sizing pass only)

baseline: Option<f32>

The baseline of this box, if applicable, measured from its content-box top edge. (14 accesses — IFC/table alignment)

inline_layout_result: Option<CachedInlineLayout>

Cached inline layout result with the constraints used to compute it.

This field stores both the computed layout AND the constraints (available width, float state) under which it was computed. This is essential for correctness:

• Table cells are measured multiple times with different widths
• Min-content/max-content intrinsic sizing uses special constraint values
• The final layout must use the actual available width, not a measurement width

By tracking the constraints, we avoid the bug where a min-content measurement (with width=0) would be incorrectly reused for final rendering. (13 accesses — IFC roots / table cells)

scrollbar_info: Option<ScrollbarRequirements>

Cached scrollbar information (calculated during layout) Used to determine if scrollbars appeared/disappeared requiring reflow (12 accesses — scrollable containers only)

relative_position: Option<LogicalPosition>

The position of this node relative to its parent’s content box. (9 accesses — positioning pass)

overflow_content_size: Option<LogicalSize>

The actual content size (children overflow size) for scrollable containers. This is the size of all content that might need to be scrolled, which can be larger than used_size when content overflows the container. (7 accesses — scrollable containers)

taffy_cache: Cache

Cache for Taffy layout computations for this node. (6 accesses — Taffy bridge)

computed_style: ComputedLayoutStyle

Pre-computed CSS properties needed during layout. Computed once during layout tree build to avoid repeated style lookups. (5 accesses — cache.rs only)

pseudo_element: Option<PseudoElement>

Pseudo-element type (::marker, ::before, ::after) if this node is a pseudo-element (5 accesses — pseudo-elements only)

escaped_top_margin: Option<f32>

Escaped top margin (CSS 2.1 margin collapsing) If this BFC’s first child’s top margin “escaped” the BFC, this contains the collapsed margin that should be applied by the parent. (4 accesses — BFC margin collapsing)

escaped_bottom_margin: Option<f32>

Escaped bottom margin (CSS 2.1 margin collapsing)
If this BFC’s last child’s bottom margin “escaped” the BFC, this contains the collapsed margin that should be applied by the parent. (4 accesses)

parent_formatting_context: Option<FormattingContext>

Parent’s formatting context (needed to determine if stretch applies) (4 accesses — flex/grid children)

ifc_membership: Option<IfcMembership>

If this node participates in an IFC (is inline content like text), stores the reference back to the IFC root and the run index. This allows text nodes to find their layout data in the parent’s IFC. (3 accesses — text nodes only)

containing_block_index: Option<usize>

The layout tree index of this node’s containing block.

• For abs-pos elements: nearest positioned (non-static) ancestor
• For fixed elements: root / None (viewport)
• For normal-flow: parent (None = implicit) Used for clip exemption: abs-pos elements whose containing block is above an overflow clipper should not be clipped.

anonymous_type: Option<AnonymousBoxType>

Type of anonymous box (if applicable) (2 accesses)

node_data_fingerprint: NodeDataFingerprint

Multi-field fingerprint of this node’s data (style, text, etc.) for granular change detection during reconciliation. (2 accesses — reconciliation only)

subtree_hash: SubtreeHash

A hash of this node’s data and all of its descendants. Used for fast reconciliation. (9 accesses — all in cache.rs reconciliation)

dirty_flag: DirtyFlag

Dirty flags to track what needs recalculation. (7 accesses — reconciliation setup)

unresolved_box_props: UnresolvedBoxProps

Unresolved box model properties (raw CSS values). These are resolved lazily during layout when containing block is known. (1 access — initial resolution only)

ifc_id: Option<IfcId>

If this node is an IFC root, stores the IFC ID. Used to identify which IFC this node’s inline_layout_result belongs to. (1 access — IFC creation only)

Implementations

impl LayoutNode

pub fn split(self) -> (LayoutNodeHot, LayoutNodeWarm, LayoutNodeCold)

Split this full layout node into hot/warm/cold components. Used during LayoutTreeBuilder::build() to create the SoA layout.

Trait Implementations

impl Clone for LayoutNode

fn clone(&self) -> LayoutNode

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for LayoutNode

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.