This is preparation for allowing blocks with their own internal BFC to
flow around floating boxes in the parent BFC.
Note that IFC still has the available_space_for_line() API, which
returns space available within the IFC's own containing block, while the
BFC available_space_for_line() returns space available within its root.
Previously, these were added during layout. This didn't fit into the new
world where layout doesn't mutate the tree incrementally, so this patch
adds logic to Layout::TreeBuilder for adding a marker to each list-item
box after its children have been constructed.
This patch adds a map of Layout::Node to FormattingState::NodeState.
Instead of updating layout nodes incrementally as layout progresses
through the formatting contexts, all updates are now written to the
corresponding NodeState instead.
At the end of layout, FormattingState::commit() is called, which
transfers all the values from the NodeState objects to the Node.
This will soon allow us to perform completely non-destructive layouts
which don't affect the tree.
Note that there are many imperfections here, and still many places
where we assign to the NodeState, but later read directly from the Node
instead. I'm just committing at this stage to make subsequent diffs
easier to understand.
The purpose of this new object will be to keep track of various states
during an ongoing layout.
Until now, we've been updating layout tree nodes as we go during layout,
which adds an invisible layer of implicit serialization to the whole
layout system.
My idea with FormattingState is that running layout will produce a
result entirely contained within the FormattingState object. At the end
of layout, it can then be applied to the layout tree, or simply queried
for some metrics we were trying to determine.
When doing subtree layouts to determine intrinsic sizes, we will
eventually be able to clone the current FormattingState, and run the
subtree layout in isolation, opening up opportunities for parallelism.
This first patch doesn't go very far though, it merely adds the object
as a skeleton class, and makes sure the root BFC has one. :^)
Normally we don't layout position:absolute elements until after the
parent formatting context has assigned dimensions to the current
formatting context's root box.
However, some of our parent contexts (especially FFC) don't do this
reliably, which makes position:absolute children have 0x0 dimensions.
Hack this for now by making ~BFC() pretend that the parent assigned
dimensions if it hadn't done it already.
Until now, some formatting contexts (BFC in particular) have been
assigning size to the root box. This is really the responsibility of the
parent formatting context, so let's stop doing it.
To keep position:absolute working, parent formatting contexts now notify
child contexts when the child's root box has been sized. (Note that the
important thing here is for the child root to have its final used height
before it's able to place bottom-relative boxes.)
This breaks flexbox layout in some ways, but we'll have to address those
by improving the spec compliance of FFC.)
Block placement is now divided into a vertical and horizontal step. The
vertical step runs before formatting boxes internally. The horizontal
step still runs after (since we may need the final width value.)
This solves a long-standing architectural problem where IFC didn't know
its origin Y position within the BFC root box. This is required for
figuring out how to flow around floating objects. (Floating objects are
always relative to the BFC root.)
If we run out of horizontal space when placing floating objects,
we now perform a "break" and continue with a new line of floats
below the bottommost margin edge of the current line.
This is definitely not 100% to-spec yet, but a huge improvement
on ACID1 already. :^)
This patch adds a BFC::FloatSideData struct so we can contain left and
right floating object layout state in a struct. This is preparation for
adding more per-side state.
Per the spec, only a BlockContainer" can have line boxes, so let's not
clutter up every Layout::Box with line boxes.
This also allows us to establish an invariant that BFC and IFC always
operate on a Layout::BlockContainer.
Note that if BlockContainer has all block-level children, its line boxes
are not used for anything. They are only used in the all inline-level
children scenario.
The CSS spec uses the name "block formatting context root" when talking
about a box that establishes a BFC. So let's call it BFC::root() in our
code as well, instead of the less specific BFC::context_box().
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
This commit fixes algorithm for computing auto height (CSS 2.2 10.6.7)
by including floating boxes into computation and implements one of the cases
for computing the height of absolutely positioned, non-replaced elements (10.6.4 rule 3)
Section 10.3 "Calculating widths and margins" indicates that the 'left'
and 'right' properties of relatively positioned elements should be set
in accordance with the rules of section 9.4.3.
Auto block heights are now computed according to something that kinda
resembles the specification.
Blocks with inline children and height:auto have their height computed
based on the top of the first line box and the bottom of the last line
box. Very straightforward.
Blocks with block children and height:auto have their height computed
based on the top of the first in-flow block child's margin box, and the
bottom of the last in-flow block child's margin box.
