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LibWeb: Make LayoutState use HashMap instead of potentially huge Vector

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Before this change, LayoutState essentially had a Vector<UsedValues*>
resized to the exact number of layout nodes in the current document.

When a nested layout is performed (to calculate the intrinsic size of
something), we make a new LayoutState with its own Vector. If an entry
is missing in a nested LayoutState, we check the parent chain all the
way up to the root.

Because each nested LayoutState had to allocate a new Vector with space
for all layout nodes, this could get really nasty on very large pages
(such as the ECMA262 specification).

This patch replaces the Vector with a HashMap. There's now a small cost
to lookups, but what we get in return is the ability to handle huge
layout trees without spending eternity in page faults.
This commit is contained in:
Andreas Kling 2023-05-23 07:47:37 +02:00
parent e83681ee34
commit e2c72922f6
6 changed files with 35 additions and 42 deletions
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2
Userland/Libraries/LibWeb/DOM/Document.cpp
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@ -859,13 +859,11 @@ void Document::update_layout()
auto viewport_rect = browsing_context()->viewport_rect();
if (!m_layout_root) {
m_next_layout_node_serial_id = 0;
Layout::TreeBuilder tree_builder;
m_layout_root = verify_cast<Layout::Viewport>(*tree_builder.build(*this));
}
Layout::LayoutState layout_state;
layout_state.used_values_per_layout_node.resize(layout_node_count());
{
Layout::BlockFormattingContext root_formatting_context(layout_state, *m_layout_root, nullptr);