Properly position floats when subsequent boxes collapse margins with containing block (2)
PR #29939 tried to address this but missed various cases.
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Clearance was implemented as a Length, where zero meant no clearance.
However, having a clearance of 0px should be different than having
no clearance, since the former can still prevent margin collapse.
This patch keeps the existing behavior, so it won't be possible to get
a clearance of Some(Length::zero()), but it prepares the terrain for
a follow-up to fix calculate_clearance to return the proper thing.
Margins should be able to collapse through floats when collapsing with
parent blocks (the containing block). To properly place floats in this
situation, we need to look at these subsequent floats to find out how
much of the margin will collapse with the parent.
This initial implementation is very basic and the second step would be
to cache this in order to avoid having to constantly recalculate it.
Fixes#29915.
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Previously, final float positions were calculated when their parents
were positioned. This prevented proper positioning of absolute children
of floats with static insets, because they accumulate offsets as they
are hoisted up the tree.
This change moves the final float positioning to
`PlacementState::place_fragment` for the float itself so that it happens
before any insets are updated for hoisted descendants. In addition to
simplifying the code, this makes it a bit more efficient. Finally,
floats are taken into account when updating static insets of hoisted
boxes.
Fixes#29826.
In #29897 I did the simple naive thing, but it wasn't entirely correct.
This patch tries to address the problems. In particular:
- Clearance should prevent margins from collapsing through if it
happens between them, as opposed to on the element that owns them.
- The margins of an element with clearance can still collapse through,
and collapse with other siblings as normal, but the resulting
margin can't collapse with the bottom margin of the parent.
Simplify layout of absolutes with static insets
Absolutes with static insets need to be laid out at their ancestor containing blocks, but their position is dependent on their parent's layout. The static layout position is passed up the tree during hoisting and ancestors each add their own offset to the position until it is relative to the containing block that contains the absolute.
This is currently done with a closure and a fairly tricky "tree rank" numbering system that needs to be threaded through the entire layout. This change replaces that system.
Every time a child is laid out we create a positioning context to hold any absolute children (this can be optimized away at a later time). At each of these moments, we call a method to aggregate offsets to the static insets of hoisted absolutes. This makes the logic easier to follow and will also allow implementing this behavior for inline-blocks, which was impossible with the old system.
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Prevent margins from collapsing through when separated by clearance
This fixes#29884 and improves #29896.
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Layout 2020: Correct rendering of floated root
Fix two issues around floating a root element:
1. In the StackingContext code handle the case where a root element is a Float fragment and not a Box fragment. This fixes a debug assertion failure in the css/CSS2/float/float-root.html test.
2. When initializing the SequentialLayoutState, use the containing block width as the maximum inline float placement position instead of infinity. This fixes the rendering of css/CSS2/float/float-root.html.
Note that css/CSS2/float/float-root.html was passing before, because both the test and reference were subject to the same bug. This fixes a couple other tests as well.
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Fix two issues around floating a root element:
1. In the StackingContext code handle the case where a root element is a
Float fragment and not a Box fragment. This fixes a debug assertion
failure in the css/CSS2/float/float-root.html test.
2. When initializing the SequentialLayoutState, use the containing block
width as the maximum inline float placement position instead of
infinity. This fixes the rendering of css/CSS2/float/float-root.html.
Note that css/CSS2/float/float-root.html was passing before, because
both the test and reference were subject to the same bug. This fixes a
couple other tests as well.
Absolutes with static insets need to be laid out at their ancestor
containing blocks, but their position is dependent on their parent's
layout. The static layout position is passed up the tree during hoisting
and ancestors each add their own offset to the position until it is
relative to the containing block that contains the absolute.
This is currently done with a closure and a fairly tricky "tree rank"
numbering system that needs to be threaded through the entire layout.
This change replaces that system.
Every time a child is laid out we create a positioning context to hold
any absolute children (this can be optimized away at a later time). At
each of these moments, we call a method to aggregate offsets to the
static insets of hoisted absolutes. This makes the logic easier to
follow and will also allow implementing this behavior for inline-blocks,
which was impossible with the old system.
Typically, block-level contents are stacked vertically, so this was just
taking the maximum size among all contents. However, floats can be
stacked horizontally, so we need to sum their sizes.
Implement BlockLevelBox::inline_content_sizes for floats
This improves #29874, but `BlockContainer::inline_content_sizes` will still need more changes in order to correctly handle sequences of floats.
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Fix some rustdoc comments which won't process properly unless they start
with three '/' characters. In addition, improve the name of a function
and add some missing documentation.
According to https://drafts.csswg.org/css2/#collapsing-margins, bottom
margins should only collapse with the last child if `height` is `auto`.
Also, the note mentions `min-height: 0`, but the normative text doesn't
have such requirement, so I'm dropping it, matching WebKit.
The previous logic is moved into the case of collapsing the top and
bottom margins of the same element, since this can happen either with
`height: auto` or `height: 0`, and requires `min-height: 0`.
Layout 2020: Move all Fragment code to the `fragment_tree` directory
This is a simple code organization change with no behavior change with the idea of making Layout 2020 easier to understand by new folks to the project. The idea is that we will have a cleaner separation between the different parts of layout ie one directory for the fragment tree and one (currently multiple) directory for the box tree.
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This is a simple code organization change with no behavior change with
the idea of making Layout 2020 easier to understand by new folks to the
project. The idea is that we will have a cleaner separation between the
different parts of layout ie one directory for the fragment tree and one
(currently multiple) directory for the box tree.
Instead of hoisting floated fragments to be siblings of the fragment
created by their containing block formatting context, keep them in
"normal" fragment tree position and adjust their positioning to be
relative to the containing block. This means that float fragments follow
the existing invariants of the fragment tree and properly handle hit
testing, painting order, and relative positioning.
The tradeoff here is more complexity tracking the containing block
offsets from the block formatting context (including handling collapsed
margins), but less complexity dealing with hoisting / shared ownership
in addition to the correctness benefits.
Some tests are failing now because this change revealed some additional
shortcomings with clearing block formatting context content size past
the end of their contained floats. This will be fixed in a followup
change.
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
This commit puts floats behind the `layout.floats.enabled` pref, because of the
following issues and unimplemented features:
* Inline formatting contexts don't take floats into account, so text doesn't
flow around the floats yet.
* Non-floated block formatting contexts don't take floats into account, so BFCs
can overlap floats.
* Block formatting contexts that contain floats don't expand vertically to
contain all the floats. That is, floats can stick out the bottom of BFCs,
contra spec.
During layout it is often useful, for various specification reasons, to
know if an element is the `<body>` element of an `<html>` element root. There
are a couple places where a brittle heuristic is used to detect `<body>`
elements. This information is going to be even more important to
properly handle `<html>` elements that inherit their overflow property from
their `<body>` children.
Implementing this properly requires updating the DOM wrapper interface.
This check does reach up to the parent of thread-safe nodes, but this is
essentially the same kind of operation that `parent_style()` does, so is
ostensibly safe.
This change should not change any behavior and is just a preparation
step for properly handle `<body>` overflow.
Manage containing blocks and WebRender SpaceAndClip during stacking
context tree constuction using the ContainingBlockInfo data structure.
This will allow us to reuse this data structure whenever we traverse the
fragment tree. In addition, StackingContextBuilder is no longer
necessary at all. This change also fixes some bugs where fixed position
fragments were not placed in the correct spatial node. Unfortunately,
these fixes are difficult to test because of #29659.
context, to place floats in layout 2020.
The containing block for a float is not necessarily the same as the block
formatting context the float is in per CSS 2.1 [1]:
"For other elements, if the element’s position is relative or static, the
containing block is formed by the content edge of the nearest block container
ancestor box."
This shows up in the simplest case:
<html>
<body>
<div style="float: left">Hello</div>
</body>
</html>
In this case, the `<html>` element is the block formatting context with inline
size equal to the width of the window, but the `<body>` element with nonzero
inline margins is the containing block for the float. The float placement must
respect the content box of the `<body>` element (i.e. floats must not overlap
the `<body>` element's margins), not that of the `<html>` element.
Because a single block formatting context may contain floats with different
containing blocks, the left and right "walls" of that containing block become
properties of individual floats at the time of placement, not properties of the
float context itself.
Additionally, this commit generalizes the float placement logic a bit to allow
the placement of arbitrary objects, not just floats. This is intended to
support inline layout and block formatting context placement.
This commit updates the `FloatContext` and associated tests only and doesn't
actually wire the context up to the rest of layout, so floats in pages still
aren't actually laid out.
[1]: https://drafts.csswg.org/css2/#containing-block-details
2020, not yet wired to the rest of layout.
This commit implements an object that handles the 10 rules in CSS 2.1:
https://www.w3.org/TR/CSS2/visuren.html#float-position
The implementation strategy is that of a persistent balanced binary search tree
of float bands. Binary search trees are commonly used for implementing float
positioning; e.g. by WebKit. Persistence enables each object that interacts
with floats to efficiently contain a snapshot of the float list at the time
that object was laid out. That way, incremental layout can invalidate and start
reflow at any point in a containing block.
This commit features extensive use of
[QuickCheck](https://github.com/BurntSushi/quickcheck) to ensure that the rules
of the CSS specification are followed.
Because this is not yet connected to layout, floats will not actually be laid
out in Web pages yet.
Note that unit tests as set up in Servo currently require types that they
access to be public. Therefore, some internal layout 2020 types that were
previously private have been made public. This is somewhat unfortunate.
Part of #25167.
… and converting them to flow-relative geometric values.
These values are almost always used to size and position a fragment within its containing block, so using the mode of the containing block seems more correct.
Note that the `writing-mode` and `direction` properties are disabled in Servo at the moment, so this PR by itself should have no effect: the writing mode of an element is always the same of that of its containing block since they’re both horizontal rtl.
We want to mutate them when lazily computing their content sizes, but they
are behind an Arc for the hoisting infra, so it also needs its own layer
of inner mutability.
We want to compute content sizes on demand rather than eagerly so we will
need to mutate the independent formatting contexts that own the content sizes.
