Introduce AbsposContainingBlockInfo and a virtual
resolve_abspos_containing_block_info() method on FormattingContext that
computes the containing block rect, per-axis positioning mode (static
position vs inset-from-rect), and optional grid alignment — all in one
place.
The base implementation handles the common case: padding-box rect of
the containing block, with inline containing block support. GFC
overrides it to return the grid area rect with alignment info.
This replaces the per-context abspos loops that BFC, FFC, TFC, and GFC
each had, with a shared layout_absolutely_positioned_children() +
layout_absolutely_positioned_element() pair. The offset computation is
simplified from ~40 lines of branching to a data-driven dispatch on the
axis mode, and GFC's ~130-line custom layout method is replaced by a
~30-line resolve override.
Replace content_box_rect_in_static_position_ancestor_coordinate_space()
which walked the ancestor chain to compute the offset between an abspos
element's static position containing block and its actual containing
block.
Instead, add a cumulative_offset() method to UsedValues that computes
the absolute offset from the ICB to a box's content edge by walking the
containing block chain. For pre-populated nodes during partial relayout,
it returns a cached value from the paintable's absolute position.
The static-CB-to-actual-CB offset is now a simple subtraction of two
cumulative offsets, which also fixes a bug where table cells with
position:relative ancestors got incorrect static positions due to the
old function accumulating offsets in the wrong coordinate space.
Also route direct UsedValues::offset assignments in Flex, Grid, and
Table formatting contexts through set_content_offset().
Previously, horizontal padding, border, and margin were not being
resolved for table captions. This was visible in layout tests where
captions with padding showed 0 in the width metrics.
Previously, table captions were laid out using the parent's available
space before the table's width was calculated. This resulted in
captions not being properly constrained to the table's width.
Previously, `greatest_child_width()` was used, which finds the maximum
margin box width among direct children. This is incorrect for tables,
whose width is determined by column distribution rather than by simply
finding the widest child. We now return the table's computed content
width instead, which already holds the correct value after layout.
Add optional tracing that prints a tree visualization of formatting
context `run()` invocations. This is useful for debugging layout issues
where you need to understand the nesting and order of layout passes,
or why a box receives unexpected available space.
Example output:
```
├─ BFC <Viewport<#document>> run(definite(800) x definite(600))
│ ├─ BFC <BlockContainer<HTML>> run(definite(800) x indefinite)
│ │ ├─ IFC <BlockContainer(anonymous)> run(definite(800) x indefinite)
│ │ ├─ GFC <Box<DIV.grid>> run(definite(800) x indefinite)
│ │ │ ├─ BFC <BlockContainer<DIV.item>> run(definite(400) x indefinite)
```
Not every user of this requires an `auto` state, but most do.
This has quite a big diff but most of that is mechanical:
LengthPercentageOrAuto has `resolved_or_auto()` instead of `resolved()`,
and `to_px_or_zero()` instead of `to_px()`, to make their output
clearer.
When a table row (or its group) is set to collapse, the row takes up no
vertical space in the layout.
We have to account for this in multiple places, so I've cached whether a
row is collapsed in the TableGrid::Row.
We previously checked the cell's computed values for the border-collapse
property, but a cell is only in separated-borders mode if the table has
border-collapse set to separate. Curiously in some other placed where
this mode is checked we already did the correct thing.
Instead, use the generic create_independent_formatting_context_if_needed
so that unusual situations like image-as-table-caption don't crash.
This logic clearly needs more work, but let's at least do better than
crashing. This gives us 26 new subtest passes on WPT.
positioned element is a descendant of inline-block
Sets inline block offsets in InlineFormattingContext.cpp, but this is
not enough. When static position rect is calculated during layout,
not all ancestors of abspos box may have their offsets calculated yet
(more info here: https://github.com/LadybirdBrowser/ladybird/pull/2583#issuecomment-2507140272).
So now static position rect is calculated relative to static containing
block during layout and calculation relative to actual containing block
is done later in
FormattingContext::layout_absolutely_positioned_element.
Fixes wpt/css/CSS2/abspos/static-inside-inline-block.html
Explicitly pass containing block width in
resolve_vertical_box_model_metrics() instead of doing containing block
box lookup.
This is a part of refactoring towards removing containing_block() usage
that will allow us introduce partial layout.
The BFC "context box" is now the outer box of the block formatting
context. Previously the context box was always the current target box,
which made it hard to reason about who was really the containing block
of whom in various places.
Note that IFC still has the containing block as its context box, this
change only affects BFC. However, to clarify the situation in IFC,
I've added a containing_block() getter than returns the context_box().
Bring the names of various boxes closer to spec language. This should
hopefully make things easier to understand and hack on. :^)
Some notable changes:
- LayoutNode -> Layout::Node
- LayoutBox -> Layout::Box
- LayoutBlock -> Layout::BlockBox
- LayoutReplaced -> Layout::ReplacedBox
- LayoutDocument -> Layout::InitialContainingBlockBox
- LayoutText -> Layout::TextNode
- LayoutInline -> Layout::InlineNode
Note that this is not strictly a "box tree" as we also hang inline/text
nodes in the same tree, and they don't generate boxes. (Instead, they
contribute line box fragments to their containing block!)
This is a first (huge) step towards modernizing the layout architecture
and bringing it closer to spec language.
Layout is now performed by a stack of formatting contexts, operating on
the box tree (or layout tree, if you will.)
There are currently three types of formatting context:
- BlockFormattingContext (BFC)
- InlineFormattingContext (IFC)
- TableFormattingContext (TFC)
Document::layout() creates the initial BlockFormattingContext (BFC)
which lays out the initial containing block (ICB), and then we recurse
through the tree, creating BFC, IFC or TFC as appropriate and handing
over control at the context boundaries.
The majority of this patch is just refactoring the old logic spread out
in LayoutBlock and LayoutTableRowGroup, and turning into these context
classes instead. A lot more cleanup will be needed.
There are many architectural wins here, the main one being that layout
is no longer performed by boxes themselves, which gives us much greater
flexibility in the outer/inner layout of a given box.
