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.
The specification dictates quite quite idiosyncratic return values when
querying insets of positioned elements via getComputedStyle(). These
depend on whether or not the elements size was overconstrained. This
change adds a better implementation of that in preparation for returning
proper values for position: sticky.
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.
This change adds support for the <iframe> element to Layout 2020. In
addition, certain aspects of the implementation are made the same
between both layout systems.
This implementation is more-or-less on par with the one from layout_2013
and in some cases better. There are still some cases where we don't
return the correct "resolved value," but this is enough to test
animations and transitions.
This avoids the use of lookup tables for containing blocks when
constructing the stacking context tree.
This seems to catch some laid-out hoisted fragments that were otherwise
dropped in the previous design. The changes cause one new test to pass
and one to fail. Visual examination of the failing tests reveals that
it's a progression (list markers are appearing when they were previously
not rendered).
layout_2020: Use ArcRefCell in the fragment tree
This will allow mutability which is useful for things like animations.
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Partial text decoration support for layout 2020
- [X] `./mach build -d` does not report any errors
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- [X] These changes fix#25166
- [X] There are tests for these changes
When calculating scrolling overflow calculation we cannot currently use
the actual containing block in all cases. This change increases the
amount that we do use the containing block.
Instead of painting hoisted position fragments in the order to which
they are hoisted, paint them in tree order and properly incorporate them
into the stacking context.
We do this by creating a placeholder fragment in the original tree position
of hoisted fragments. The ghost fragment contains an atomic id which
links back to the hoisted fragment in the containing block.
While building the stacking context, we keep track of containing blocks
and their children. When encountering a placeholder fragment we look at
the containing block's hoisted children in order to properly paint the
hoisted fragment.
One notable design modification in this change is that hoisted fragments
no longer need an AnonymousFragment as their parent. Instead they are
now direct children of the fragment that establishes their containing block.
