Move the layout tree from GC allocation to refcounted ownership so
removed layout and paint subtrees are destroyed synchronously instead
of waiting for the next GC sweep. This dramatically reduces GC memory
usage peaks after layout tree churn and makes it easier for memory use
to fall back after large document updates.
Update layout factories, tree traversal, SVG layout node creation,
paintable back-pointers, and pseudo-element layout links to use RefPtr
ownership.
Make display: contents follow the same shape as Blink and WebKit: the
element itself does not create a layout node, and its children are
flattened into the nearest layout parent. Wrap direct non-whitespace
text in an anonymous inline node when the boxless element contributes
inherited style to that text.
Use an internal inline wrapper for display: contents pseudo-elements
so generated content can still participate in layout, painting, hit
testing, and pseudo-element queries. Keep CSSOM reporting the computed
display value from the pseudo style, not the internal wrapper.
Remove the retained out-of-tree layout node list and its testing hook,
since the flattened model does not need a side owner for boxless
elements. Add coverage for inherited text style, dynamic insertion
order, pseudo-element hit testing, and computed style queries.
Move ComputedProperties and CascadedProperties out of the GC. They no
longer contain strong references to GC-managed data.
Keep computed styles alive from DOM elements and animation updates with
RefPtr. Pass style into layout constructors by reference, since layout
only copies the values it needs while building nodes.
Use GC::Weak for cascade source links, so entries no longer keep the
style declaration or shadow root alive.
The Paintable tree and its supplemental painting data structures were
GC allocated because that was the easiest way to manage it and avoid
leaks introduced by ref cycles. This included the Paintable subclasses
themselves plus StackingContext, ChromeWidget, Scrollbar, ResizeHandle,
and scroll-frame state.
We are now trying to reduce GC allocation churn on layout and painting
updates, so keeping this short-lived rendering tree outside the JS heap
is a better fit. Move Paintable to RefCountedTreeNode, make painting
helpers ref-counted or weakly reference Paintables, and update the
layout and event-handler call sites to use RefPtr/WeakPtr ownership.
Instead, compute them on demand. This affects ReplacedBox and its
subclasses.
This commit is centered around a new Box::auto_content_box_size
method. It returns a SizeWithAspectRatio representing the natural
size of a replaced element, or the size derived from attributes
for text input and textarea. These values are used when the
corresponding axis is auto or indefinite.
Although introducing this API choke-point for sizing replaced and
replaced-like elements was the main goal, it's notable that layout
becomes more robust in the face of dynamic changes due to reduced
potential for stale size values (at the cost of extra calculations
and allocations).
This gets rid of the assumption that the DOM node of an ImageBox is
also its image provider. This will become necessary when generating
the image boxes for view transition pseudos, for which the DOM node
won't be the image provider. (that'll be the pseudo element itself)
Resulting in a massive rename across almost everywhere! Alongside the
namespace change, we now have the following names:
* JS::NonnullGCPtr -> GC::Ref
* JS::GCPtr -> GC::Ptr
* JS::HeapFunction -> GC::Function
* JS::CellImpl -> GC::Cell
* JS::Handle -> GC::Root
Bring the names of various boxes closer to spec language. This should
hopefully make things easier to understand and hack on. :^)
Some notable changes:
- LayoutNode -> Layout::Node
- LayoutBox -> Layout::Box
- LayoutBlock -> Layout::BlockBox
- LayoutReplaced -> Layout::ReplacedBox
- LayoutDocument -> Layout::InitialContainingBlockBox
- LayoutText -> Layout::TextNode
- LayoutInline -> Layout::InlineNode
Note that this is not strictly a "box tree" as we also hang inline/text
nodes in the same tree, and they don't generate boxes. (Instead, they
contribute line box fragments to their containing block!)
2020-11-22 15:56:27 +01:00
Renamed from Libraries/LibWeb/Layout/LayoutImage.cpp (Browse further)
