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LibWeb: Make Layout::FormattingState copies shallow

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Previously, each NodeState in a FormattingState was shared with the
parent FormattingState, but the HashMap of NodeState had to be copied
when making FormattingState copies.

This patch makes copying instant by keeping a pointer to the parent
FormattingState instead. When fetching immutable state via get(), we may
now return a reference to a NodeState owned by a parent FormattingState.

get_mutable() will copy any NodeState found in the ancestor chain before
making a brand new one.
This commit is contained in:
Andreas Kling 2022-03-12 16:33:11 +01:00
parent b6097cf724
commit 515db5fc1b
4 changed files with 40 additions and 30 deletions
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26
Userland/Libraries/LibWeb/Layout/FormattingState.h
View file

@ -15,6 +15,12 @@
namespace Web::Layout {
struct FormattingState {
FormattingState() { }
explicit FormattingState(FormattingState const* parent)
: m_parent(parent)
{
}
struct NodeState {
float content_width { 0 };
float content_height { 0 };
@ -65,31 +71,17 @@ struct FormattingState {
}
Optional<LineBoxFragmentCoordinate> containing_line_box_fragment;
// NOTE: NodeState is ref-counted and accessed via copy-on-write helpers below.
size_t ref_count { 1 };
void ref()
{
VERIFY(ref_count);
++ref_count;
}
void unref()
{
VERIFY(ref_count);
if (!--ref_count)
delete this;
}
};
void commit();
// NOTE: get_mutable() will CoW the NodeState if it's shared with another FormattingContext.
// NOTE: get_mutable() will CoW the NodeState if it's inherited from an ancestor state;
NodeState& get_mutable(NodeWithStyleAndBoxModelMetrics const&);
// NOTE: get() will not CoW the NodeState.
NodeState const& get(NodeWithStyleAndBoxModelMetrics const&) const;
HashMap<NodeWithStyleAndBoxModelMetrics const*, NonnullRefPtr<NodeState>> nodes;
HashMap<NodeWithStyleAndBoxModelMetrics const*, NonnullOwnPtr<NodeState>> nodes;
// We cache intrinsic sizes once determined, as they will not change over the course of a full layout.
// This avoids computing them several times while performing flex layout.
@ -98,6 +90,8 @@ struct FormattingState {
Gfx::FloatSize max_content_size;
};
HashMap<NodeWithStyleAndBoxModelMetrics const*, IntrinsicSizes> mutable intrinsic_sizes;
FormattingState const* m_parent { nullptr };
};
Gfx::FloatRect absolute_content_rect(Box const&, FormattingState const&);