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LibWeb: Reduce paintable tree traversals during hit-testing

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By storing a list of positioned and floating descendants within the
stacking context tree node, we can eliminate the need for costly
paintable tree traversals during hit-testing.

This optimization results in hit-testing being 2 to 2.5 times faster
on https://ziglang.org/documentation/master/
This commit is contained in:
Aliaksandr Kalenik 2024-03-01 11:54:44 +01:00 • committed by Andreas Kling
parent 9c6c3fe0d8
commit 2764966ccc
5 changed files with 95 additions and 77 deletions
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9
Userland/Libraries/LibWeb/Painting/ViewportPaintable.cpp
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@ -38,11 +38,16 @@ void ViewportPaintable::build_stacking_context_tree()
size_t index_in_tree_order = 1;
for_each_in_subtree([&](Paintable const& paintable) {
const_cast<Paintable&>(paintable).invalidate_stacking_context();
if (!paintable.layout_node().establishes_stacking_context()) {
auto* parent_context = const_cast<Paintable&>(paintable).enclosing_stacking_context();
auto establishes_stacking_context = paintable.layout_node().establishes_stacking_context();
if ((paintable.is_positioned() || establishes_stacking_context) && paintable.computed_values().z_index().value_or(0) == 0)
parent_context->m_positioned_descendants_with_stack_level_0_and_stacking_contexts.append(paintable);
if (!paintable.is_positioned() && paintable.is_floating())
parent_context->m_non_positioned_floating_descendants.append(paintable);
if (!establishes_stacking_context) {
VERIFY(!paintable.stacking_context());
return TraversalDecision::Continue;
}
auto* parent_context = const_cast<Paintable&>(paintable).enclosing_stacking_context();
VERIFY(parent_context);
const_cast<Paintable&>(paintable).set_stacking_context(make<Painting::StackingContext>(const_cast<Paintable&>(paintable), parent_context, index_in_tree_order++));
return TraversalDecision::Continue;