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LibWeb: Fix O(n^2) traversal in hit testing

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We already walk the entire paint tree within each stacking context in
the main hit testing function (StackingContext::hit_test()), so there's
no need for each individual paintable to walk its own children again.

By not doing that, we remove a source of O(n^2) traversal which made hit
testing on deeply nested web pages unbearably slow.
This commit is contained in:
Andreas Kling 2022-03-21 12:12:50 +01:00
parent f7cfd47b48
commit 996f3228a2
2 changed files with 8 additions and 18 deletions
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15
Userland/Libraries/LibWeb/Painting/StackingContext.cpp
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@ -297,9 +297,8 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
// 6. the child stacking contexts with stack level 0 and the positioned descendants with stack level 0.
m_box.for_each_in_subtree_of_type<Layout::Box>([&](Layout::Box const& box) {
if (box.is_positioned() && !box.paint_box()->stacking_context()) {
result = box.paint_box()->hit_test(transformed_position, type);
if (result.has_value())
return IterationDecision::Break;
if (auto candidate = box.paint_box()->hit_test(transformed_position, type); candidate.has_value())
result = move(candidate);
}
return IterationDecision::Continue;
});
@ -316,9 +315,8 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
// 4. the non-positioned floats.
m_box.for_each_in_subtree_of_type<Layout::Box>([&](Layout::Box const& box) {
if (box.is_floating()) {
result = box.paint_box()->hit_test(transformed_position, type);
if (result.has_value())
return IterationDecision::Break;
if (auto candidate = box.paint_box()->hit_test(transformed_position, type); candidate.has_value())
result = move(candidate);
}
return IterationDecision::Continue;
});
@ -329,9 +327,8 @@ Optional<HitTestResult> StackingContext::hit_test(Gfx::FloatPoint const& positio
if (!m_box.children_are_inline()) {
m_box.for_each_in_subtree_of_type<Layout::Box>([&](Layout::Box const& box) {
if (!box.is_absolutely_positioned() && !box.is_floating()) {
result = box.paint_box()->hit_test(transformed_position, type);
if (result.has_value())
return IterationDecision::Break;
if (auto candidate = box.paint_box()->hit_test(transformed_position, type); candidate.has_value())
result = move(candidate);
}
return IterationDecision::Continue;
});