Module Compute_helpersSource

Shared utilities for layout algorithms.

This module provides common functions used across Flexbox, Grid, and Block layout implementations. All functions are ported from taffy's compute/common module.

Sourceval compute_content_size_contribution : location:float Geometry.Point.t -> size:float Geometry.Size.t -> content_size:float Geometry.Size.t -> overflow:Style.Overflow.t Geometry.Point.t -> float Geometry.Size.t

compute_content_size_contribution ~location ~size ~content_size ~overflow computes how much a child contributes to its parent's intrinsic content size.

Algorithm:

  1. For each axis, if overflow is Visible, use max size content_size; otherwise use size
  2. If both dimensions > 0, return location + computed_size
  3. Otherwise return zero size

Only Visible overflow contributes beyond border-box. Non-visible modes (Clip, Hidden, Scroll) clamp contribution to border-box size.

Sourceval apply_alignment_fallback : free_space:float -> num_items:int -> alignment_mode:Style.Align_content.t -> is_safe:bool -> Style.Align_content.t

apply_alignment_fallback ~free_space ~num_items ~alignment_mode ~is_safe resolves alignment mode fallbacks per CSS Box Alignment spec and CSSWG issue 10154.

Fallback rules:

  1. Distributed alignments (Stretch, Space_between, Space_around, Space_evenly) fall back when num_items <= 1 or free_space <= 0: Stretch, Space_between -> Flex_start (safe); Space_around, Space_evenly -> Center (safe)
  2. When free_space <= 0 and is_safe is true, all modes -> Start

See CSS Box Alignment Module.

Sourceval compute_alignment_offset : free_space:float -> num_items:int -> gap:float -> alignment_mode:Style.Align_content.t -> layout_is_flex_reversed:bool -> is_first:bool -> float

compute_alignment_offset ~free_space ~num_items ~gap ~alignment_mode ~layout_is_flex_reversed ~is_first computes the positional offset for align-content and justify-content in both Flexbox and Grid.

For first item (is_first = true):

  • Start, Stretch, Space_between: 0
  • Flex_start: free_space if reversed, else 0
  • End: free_space
  • Flex_end: 0 if reversed, else free_space
  • Center: free_space / 2
  • Space_around: free_space / num_items / 2 (if positive), else free_space / 2
  • Space_evenly: free_space / (num_items + 1) (if positive), else free_space / 2

For subsequent items (is_first = false):

  • All non-distributed modes: gap + 0
  • Space_between: gap + free_space / (num_items - 1)
  • Space_around: gap + free_space / num_items
  • Space_evenly: gap + free_space / (num_items + 1)

Negative free_space is clamped to 0 for subsequent items.

Invariant: For Grid, gap must be 0 as Grid handles gaps separately.