This change refactors how layout is done in Layout 2020 in preparation
for a compositor-side scroll tree:
1. Now the SpatialId and ClipId of each fragment is stored separately.
This will allow storing a scroll node id instead of only the handle
to the WebRender spatial node.
2. Separate out stacking context tree construction and display list
building. This change will make it possible to eventually build the
stacking context tree without the full display list if we find that
necessary. For instance, this might be useful to cache containing
block boundaries.
3. Add a `DisplayList` struct that stores both the WebRender display
list builder and the compositor info. This exposes the API to the
layout thread for display list building.
In addition, this change adds a lot of missing documentation. This
should not change behavior.
Detect body elements during layout
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.
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- [x] `./mach build -d` does not report any errors
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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.
WebRender already seems to be doing this normalization, but this is
needed by inner_radii in order to properly compute the reduced radii
when background-clip is content-box or padding-box.
This will also be needed for expanding the radii for box-shadow or
outline.
Test: css/css-backgrounds/background-rounded-image-clip-002.html
Fix corner clipping typos in layout-2020
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inner_radii() had a minus sign that shouldn't be there.
And padding_edge_clip() and content_edge_clip() clearly need to to use
the padding_rect() and content_rect() instead of border_rect.
Tests:
- css/css-backgrounds/background-clip-padding-box-with-border-radius.html
- css/css-backgrounds/background-rounded-image-clip.html
---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#29683 (GitHub issue number if applicable)
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- [X] There are tests for these changes OR
- [ ] These changes do not require tests because ___
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inner_radii() had a minus sign that shouldn't be there.
And padding_edge_clip() and content_edge_clip() clearly need to to use
the padding_rect() and content_rect() instead of border_rect.
Tests:
- css/css-backgrounds/background-clip-padding-box-with-border-radius.html
- css/css-backgrounds/background-rounded-image-clip.html
Previously the thickness coming from font metrics could be something
like 0.7px, so with 1dppx it would be painted as either 1 or 0 device
pixels.
Enforcing at least 1 device pixel ensures that the decoration will be
visible, and rounding to an integral amount of device pixels ensures
that the thickness won't vary depending on the position.
The specification requires this behavior when text-decoration-thickness
is set to a length or percentage. It's not clear if it should also
happen by default, but this seems to match other browsers (except for
WebKit rounding up instead of to the nearest integer).
The test text-decoration-thickness-from-zero-sized-font.html is now
failing because of #29675.
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.
Store hit testing information in a data structure that sits alongside
the display list in the compositor. This will allow the compositor to
store more information per-node. The data structure also takes care of
de-duplicating information between successive display list entries. In
the future, the data structure can be even more aggressive in producing
smaller side hit testing lists, if necessary.
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 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.
This makes it so that position:fixed elements do not scroll with the
rest of the contents, but does not tackle the rest of the issues with
their positioning.
