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
- [X] `./mach test-tidy` does not report any errors
- [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.
Add support for tracking containing blocks when doing inline layout.
This requires setting up a PositioningContext for inline boxes when
necessary. Instead of using the PositioningContext helper methods
and we reuse the contexts between line breaks.
Fixes#25279.
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.
This is a feature that was never properly implemented in the previous
layout system. We still need to preserve their in-tree order in the
display list though.
This method doesn't actually do any layout, but converts this block to a
HoistedAbsolutelyPositionedBox which is hoisted and then laid-out with
its containing block later. This makes the code a little easier to read.
This allows rendering stacking context content in the proper order. We
also need to add a new pseudo stacking context for atomic inlines in
order to preserve proper rendering order in some cases.
This adds very rudimentary support for paint order in stacking context.
In particular z-index is now handled properly, apart from issues with
hoisted fragments.
This adds an intermediary data structure that allows the display list
builder to move through the fragment tree in stacking context painting
order. Spatial nodes are built during this phase and all display list
items are added to the end of the display list.
It's not possible anymore, in the presence of min() / max(), to split a
<length-percentage> value into a <length> and a <percentage> component.
Tweak word_spacing to do what Gecko does (resolving it in advance).
This isn't correct yet, but it is necessary to give a value in order for
scrolling from script to work. Later this should give an accurate
content box response as well as work for non-root elements.
Iits details are now private to the module.
It has a couple methods that take closures to make sure that "before" and "after" steps are done together:
* In an absolutely positioned box, take care of nested abspos (establish a new containing block, etc.)
* For a box that *might* be `position: relative`, optionally take care of the same.
Percentage `width` are treated as `auto` for the purpose of
min/max-content computation, so they also need to be considered
when testing “wether width is auto”
