This patch implements the full "old model" height algorithm from the
CSS Positioned Layout spec. I went with the old model since we don't
yet have the machinery required to implement the new model.
Also, the width calculations already follow the old model, so this
is symmetric with that. Eventually we should of course implement the new
positioned layout model.
Now that intrinsic heights (correctly) depend on the amount of available
width, we can't just cache the first calculated min-content and
max-content heights and reuse it without thinking.
Instead, we have to cache three pairs:
- min-content & max-content height with definite available width
- min-content & max-content height with min-content available width
- min-content & max-content height with max-content available width
There might be some more elegant way of solving this, but basically this
makes the cache work correctly when someone's containing block is being
sized under a width constraint.
After speaking with fantasai at CSSWG about this, it turns out I had
misunderstood intrinsic heights. I originally believed all intrinsic
sizes had to be computed with no influence from the surrounding context.
As it turns out, intrinsic heights *are* influenced by the available
width, since it's needed to determine where lines break.
The APIs for calculating min-content and max-content heights now take
the available width as inputs. This instantly improves layout in many
cases where we'd previously make things way too wide.
When an absolutely positioned box has auto insets on both sides of an
axis, it's placed according to the "static position rectangle". This is,
roughly, the rectangle a box would occupy if it were position:static
instead of position:absolute or position:fixed.
This patch implements a rough, but still significantly better,
estimation of such static positions. It gets pretty hairy in the case
where an abspos box has a parent whose children are inline.
This is a big and messy change, and here's the gist:
- AvaliableSpace is now 2x AvailableSize (width and height)
- Layout algorithms are redesigned around the idea of available space
- When doing layout across nested formatting contexts, the parent
context tells the child context how much space is available for the
child's root box in both axes.
- "Available space" replaces "containing block width" in most places.
- The width and height in a box's UsedValues are considered to be
definite after they're assigned to. Marking something as having
definite size is no longer a separate step,
This probably introduces various regressions, but the big win here is
that our layout system now works with available space, just like the
specs are written. Fixing issues will be much easier going forward,
since you don't need to do nearly as much conversion from "spec logic"
to "LibWeb logic" as you previously did.
If a flex item is itself a flex container, we were previously lying when
asked if the item created a BFC. It creates an FFC, so stop lying about
this in FormattingContext::creates_block_formatting_context().
Instead of formatting contexts flailing around to figure out from the
"inside" how much space is available on the "outside", we should
provide the amount of available space in both axes as an input to run().
This basically means that when something creates a nested formatting
context, the parent context is responsible for telling the nested context
how much space is available for layout. This information is provided
immediately when invoking run().
Note that this commit doesn't pass accurate values in all cases yet.
This first step just makes it build, and passes available values in some
cases where getting them was trivial.
This patch changes the *computed* representation of the following CSS
properties to use CSS::Size:
- width, min-width, max-width
- height, min-height, max-height
A few things had to change in order for things to keep working,
but I tried to keep the diff to a minimum.
The main trouble was that `min-width` and `max-width` can't actually be
`auto`, but they *can* be `none`. We previously treated `auto` as a
valid value (and it behaved mostly like `none`).
This function should return the automatic height of the formatting
context's root box.
Until now, we've been relying on some magical handshakes between parent
and child context, when negotiating the height of child context root
boxes. This is a step towards something more reasonable.
This remained undetected for a long time as HeaderCheck is disabled by
default. This commit makes the following file compile again:
// file: compile_me.cpp
#include <LibWeb/CSS/GridTrackSize.h>
// That's it, this was enough to cause a compilation error.
When calculating the automatic height of a BFC root, we stretch it to
contain the bottommost margin edge of floating boxes.
Before this change, we assumed that floating boxes had coordinates
relative to the BFC root, when they're actually relative to the floating
box's containing block. This may or may not be the BFC root, so we have
to use margin_box_in_ancestor_coordinate_space() to apply offsets from
all boxes in the containing block chain (up to the BFC root).
Before this change, block-level boxes were laid out vertically by
placing them after the nearest previous BlockContainer sibling. This
only worked if the preceding block-level box happened to be a
BlockContainer.
This fixes an issue where the screenshot on netsurf-browser.org was not
being laid out properly (it was `img { display: block }` which creates
a block-level ImageBox, and ImageBox is not a BlockContainer but a
ReplacedBox, so the following block-level box was skipping over the
ImageBox and being placed next to whatever was before the ImageBox..)
If absolutely positioned divs do not have a fixed position, then their
position must be calculated based off of the position of their parent
and their siblings.
Factor out the code that computes the vertical position of a Box with
respect to its siblings so that it can be used when computing the
absolutely positioned divs as well.
Previously absolutely positioned boxes could only have a % height if
their parent had a absolute height (a height in pixels, em, etc).
This broke some websites/demos such as the "Francine CSS oil painting",
which starts to appear after this commit.
Francine: https://diana-adrianne.com/purecss-francine/
Previously we were checking if values were "auto" after resolving the
"auto"-ness out of them, which didn't work. There's still a bunch of
work to do on this algorithm, but now we can at least resolve some basic
automatic height scenarios.
When calculating intrinsic sizes, we don't need to recurse into *every*
box and layout its insides. IIUC, we can skip any unconstrained box with
definite sizes in both axes. So this patch does exactly that.
This state is less static than we originally assumed, and there are
special formatting context-specific rules that say certain sizes are
definite in special circumstances.
To be able to support this, we move the has-definite-size flags from
the layout node to the UsedValues struct instead.
Before performing intrinsic sizing layout on a box, we now check if its
containing block has automatic size in the relevant axis, and if so,
we fetch the size of the nearest containing block ancestor with a size.
When calculating e.g the min-content height of some box, we would only
set its containing block's height to 0 in the temporary formatting
state. The containing block width was not touched at all.
This patch aims to do a bit better by resolving indefinite containing
block sizes to INFINITY before performing intrinsic sizing. We should
probably also find a way to resolve definite containing block sizes,
but I'll leave that for our future selves.
Due to some yet-to-be-found bug(s) in intrinsic sizing, we can sometimes
end up deciding that some box has a non-finite intrinsic size.
This will create unpleasant results, and may lead to some layout
algorithms looping infinitely, so this patch adds a safeguard where
we simply turn non-finite intrinsic sizes into zero (and complain a
little bit in the debug log.)
We were prematurely resolving the computed size values, which meant
that `auto` values were swallowed before we could resolve them via
the intrinsic aspect ratio (if present)
This patch adds a separate entry point for this kind of layout.
We override it in BFC to set up initial width/height values for the
BFC root block.
Resulting dimensions are assigned as content_width and content_height
at the end of intrinsic sizing, for each axis, if it's either "auto"
or there's a min-content or max-content constraint in effect.
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
Instead of allowing FormattingContext to instantiate an IFC for anything
that has inline children, move this logic to BFC.
This is fine, since only BFC deals with blocks having inline children
anyway.
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.
