I'm not 100% sure this is on-spec, but it seems to me that flex items
that have a specified non-auto cross size should honor that value in
its min-content and max-contribution.
When sizing the flex container under a min-content or a max-content
constraint, flex items with a used flex basis of "content" should be
sized under the same constraint.
Previously, we had three layout modes:
- Normal:
- Everything uses the computed values from CSS.
- MinContent:
- Containing blocks act as if they have 0 width.
- All line breaking opportunities are taken.
- MaxContent:
- Containing blocks act as if they have infinite width.
- Only forced line breaks are accepted.
The above was based on a set of misunderstandings of CSS sizing.
A major problem with the above was that *all* containing blocks
behaved differently during intrinsic size layout, not just the
relevant one.
With this patch there are only two layout modes:
- Normal:
- Everything uses the computed values from CSS.
- IntrinsicSizeDetermination:
- One or more boxes have size constraints applied.
There are two size constraints per layout box, set here:
- FormattingState::NodeState::width_constraint
- FormattingState::NodeState::height_constraint
They are of type SizeConstraint and can be one of None, MinContent,
or MaxContent. The default is None.
When performing an IntrinsicSizeDetermination layout, we now assign
a size constraint to the box we're trying to determine the intrinsic
size of, which is then honored by using two new helpers to query
the dimensions of containing blocks:
- FormattingContext::containing_block_width_for(Box)
- FormattingContext::containing_block_height_for(Box)
If there's a relevant constraint in effect on the Box, the size of
its containing block is adjusted accordingly.
This is essentially an implementation of the "available space"
constraints from CSS-SIZING-3. I'm sure some things will break from
this, and we'll have to deal with that separately.
Spec: https://drafts.csswg.org/css-sizing-3/#available
Before, querying any of the four intrinsic sizes would cause us to
calculate all of them (the four being min-content width/height, and
max-content width/height).
Now, the helper functions only calculate the specific intrinsic size
requested. It's then cached at the root formatting context level,
so that it's never calculated twice within the same layout pass.
In cases where flex item cross size is based on the flex line cross
size, the spec specifically says to transfer the *outer* cross size of
the line. We were ignoring the "outer" part.
This patch fixes that by subtracting the cross margins from the size.
Instead of using Optional<LengthPercentage>, we now use LengthPercentage
for these values. The initial values are all `auto`.
This avoids having to check `has_value()` in a ton of places.
Instead of recomputing the "remaining free space" per flex line,
remember it after calculating it during the "resolve flexible lengths"
step so we can reuse it later.
We were not applying the distributed space to the used offset of flex
items, as we were only assigning the margins to the layout state of the
box, not the internal FlexItem::margins.
Before we ask a replaced box about its intrinsic dimensions, we have
to "prepare" the box, which tells it to go and work out what its
intrinsic dimensions are.
I've added a FIXME about how this is silly (and clearly bug-prone)
but this patch only patches it locally in FFC for now.
When calling layout_inside() on a flex item that can't have children of
its own, layout_inside() will not return an independent formatting
context, so we need to handle that case here.
AFAICT, css-values-4 tells us that clamping numbers to a range where
min>max is okay. That means we can't use AK::clamp() since it will
VERIFY that max>=min.
This patch adds a css_clamp() helper (locally in FFC for now).
This fixes an issue where a bunch of sites were crashing due to the
VERIFY in AK::clamp().
This patch adds support for MinContent and MaxContent layout to FFC.
This means that an FFC can now calculate intrinsic sizes for the flex
container, to be used by the parent formatting context.
There are some FIXME's as usual, but this already works on basic things.
This builds on the work done by implementing the flex order CSS
property and implements flex reverse layouts by just reversing
the order and the items within each order bucket.
While calculating the minimum size for main min/max size violations
we were flooring the min size to 0 if the item doesn't have a min
main size. Instead of that determine the intrinsic min main size
of that element.
This fixes the flex: 80% 0 4/1/0 test case in the flex.html
test page.
This case was missed in a previous commit that added the
determine_min_main_size_of_child function
Before if an element didn't have a main min size we would clamp
it to a literal zero. If that element also had a flex-basis 0
it's width would end up being 0.
This patch adds a determine_min_main_size_of_child function that
will calculate the minimum main size for the box based on the
content of the box.
We use the result of that function now instead of clamping
the element main min size to 0.
This also adds one more box to the flex.html test page, which is
the same flex: 0 0 0 box but with flex-direction: column.
Before this the flex layout didn't take into account the applied
borders or padding while laying out the items.
The child's top and left borders would get painted over the
parent's borders, also due to it not taking borders into account,
children with borders would overlap each other.
Due to it not taking padding into account, the children would get
drawn outside the parent element.
The spec at https://www.w3.org/TR/css-flexbox-1/ states that when
calculating specific spaces and sizes inside a flex container, the outer
size of a flex item needs to be taken into account.
This patch adds the margins in the main dimension of a flex item to
these calculations such that their margins are actually painted in a lot
of common cases.
It makes our Github page look marginally better.
The old mode names, while mechanically accurate, didn't really reflect
their relationship to the CSS specifications.
This patch renames them as follows:
Default => Normal
AllPossibleLineBreaks => MinContent
OnlyRequiredLineBreaks => MaxContent
There's also now an explainer comment with the LayoutMode enum about the
specific implications of layout in each mode.
Simplify automatic cross sizing of items in flex-direction:column by
using the fit-content width directly.
There's obviously a lot more nuance to this, but for now this makes
flex items with both width:auto and height:auto actually get some height
in column flex layouts.
Previously, each NodeState in a FormattingState was shared with the
parent FormattingState, but the HashMap of NodeState had to be copied
when making FormattingState copies.
This patch makes copying instant by keeping a pointer to the parent
FormattingState instead. When fetching immutable state via get(), we may
now return a reference to a NodeState owned by a parent FormattingState.
get_mutable() will copy any NodeState found in the ancestor chain before
making a brand new one.
The flexbox specification barely even handwaves about automatically
sized items, but there's actually a lot of work to do in order for them
to get the correct size.
This patch is messy, but does make significant progress on supporting
flex items with indefinite width and/or height.
There's a fair amount of nested layout going on here, but do note that
we'll be hitting the intrinsic sizes cache whenever possible.
Although something has a definite size, we may still have to "resolve"
it, since FFC is quite liberal in what it considers to be definite.
Let's put that logic in a set of helper functions.
For single-line flex containers, center the only flex line along the
cross axis. Alignment of multi-line flex containers are left as a FIXME.
This patch also moves out the assignment of final metrics to the
FormattingState from align_all_flex_lines() to a separate function.
- Avoid performing inside layout on definite-size flex items (since
their computed size can be used as-is.)
- Use FormattingState::clone() to generate a throwaway layout instead of
mutating the tree in-place.
- Update spec link & comments based on current CSSWG draft. The latest
version is quite a bit clearer on how this should work.
Instead of doing internal child layout incrementally as we go, save it
for the end of flex layout. The code will become simpler if we can focus
on simply computing the dimensions of each flex item while we're doing
the main FFC algorithm.
We don't need to perform inside layout here. The only information we
need in this step is whether an anonymous block container has nothing
but empty-or-whitespace text children.
This information is already accurate after the initial layout tree
construction. Performing a layout does not change the answer. It does
however have many other side effects, so let's defer those.
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. :^)
Nobody makes undefined Lengths now, (although actually removing
Undefined will come in a later commit) so we can remove this parameter,
and `resolved_or_auto()`/`resolved_or_zero()`.
This property represents the CSS content size, so let's reduce ambiguity
by using the spec terminology.
We also bring a bunch of related functions along for the ride.
Most of the time, we cannot resolve a `calc()` expression until we go to
use it. Since any `<length-percentage>` can legally be a `calc
()`, let's store it in `LengthPercentage` rather than make every single
user care about this distinction.
Despite looking like it was still needed, it was only used for passing
to other calls to Length::resolved() recursively. This makes the
various `foo.resolved().resolved()` calls a lot less awkward.
(Though, still quite awkward.)
I think we'd need to separate calculated lengths out to properly tidy
these calls up, but one yak at a time. :^)
A lot of this is quite ugly, but it should only be so until I remove
Length::Type::Percentage entirely. (Which should happen later in this
PR, otherwise, yell at me!) For now, a lot of things have to be
resolved twice, first from a LengthPercentage to a Length, and then
from a Length to a pixel one.
The flexbox logic confuses me so regressions are possible, though our
test page looks the same as before so it should be fine.
Renamed FlexBasis::Length -> LengthPercentage too, for clarity.
This was a hack to percentages within tables relative to the nearest
table-row ancestor instead of the nearest table container.
That didn't actually make sense, so this patch simply removes the hack
in favor of containing_block()->width().
Since FFC is only ever run() on the flex container, we can assume (but
verify) that the run box is the flex container and use an accessor
throughout. The end result: less parameter passing.
Determining the available main and cross space is now done by a separate
function. The signature is a little bit hairy since this function
computes some things that are used by subsequent algorithm steps.
Factoring can definitely be improved further.
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.
There's a subtle difference here. A "block box" in the spec is a
block-level box, while a "block container" is a box whose children are
either all inline-level boxes in an IFC, or all block-level boxes
participating in a BFC.
Notably, an "inline-block" box is a "block container" but not a "block
box" since it is itself inline-level.
Auto margins are still not supported at all, but this is a good start
into supporting margins on flex items.
The way cross-before (top for row, left for column) is handled is very
naive.
