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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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86
Userland/Libraries/LibWeb/Painting/StackingContext.cpp
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@ -328,34 +328,6 @@ void StackingContext::paint(PaintContext& context) const
context.recording_painter().restore();
}
template<typename Callback>
static TraversalDecision for_each_in_inclusive_subtree_within_same_stacking_context_in_reverse(Paintable const& paintable, Callback callback)
{
if (paintable.stacking_context()) {
// Note: Include the stacking context (so we can hit test it), but don't recurse into it.
if (auto decision = callback(paintable); decision != TraversalDecision::Continue)
return decision;
return TraversalDecision::SkipChildrenAndContinue;
}
for (auto* child = paintable.last_child(); child; child = child->previous_sibling()) {
if (for_each_in_inclusive_subtree_within_same_stacking_context_in_reverse(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
if (auto decision = callback(paintable); decision != TraversalDecision::Continue)
return decision;
return TraversalDecision::Continue;
}
template<typename Callback>
static TraversalDecision for_each_in_subtree_within_same_stacking_context_in_reverse(Paintable const& paintable, Callback callback)
{
for (auto* child = paintable.last_child(); child; child = child->previous_sibling()) {
if (for_each_in_inclusive_subtree_within_same_stacking_context_in_reverse(*child, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
return TraversalDecision::Continue;
}
TraversalDecision StackingContext::hit_test(CSSPixelPoint position, HitTestType type, Function<TraversalDecision(HitTestResult)> const& callback) const
{
if (!paintable().is_visible())
@ -389,39 +361,16 @@ TraversalDecision StackingContext::hit_test(CSSPixelPoint position, HitTestType
return TraversalDecision::Break;
}
bool should_exit = false;
// 6. the child stacking contexts with stack level 0 and the positioned descendants with stack level 0.
for_each_in_subtree_within_same_stacking_context_in_reverse(paintable(), [&](Paintable const& paintable) {
VERIFY(!should_exit);
if (!paintable.is_paintable_box())
return TraversalDecision::Continue;
auto const& paintable_box = verify_cast<PaintableBox>(paintable);
auto const& z_index = paintable_box.computed_values().z_index();
auto positioned_element_without_stacking_context = paintable_box.is_positioned() && !paintable_box.stacking_context();
if (z_index.value_or(0) == 0 && (positioned_element_without_stacking_context || paintable_box.layout_node().is_grid_item())) {
if (paintable_box.hit_test(transformed_position, type, callback) == TraversalDecision::Break) {
should_exit = true;
for (auto const& paintable : m_positioned_descendants_with_stack_level_0_and_stacking_contexts.in_reverse()) {
if (paintable.stacking_context()) {
if (paintable.stacking_context()->hit_test(transformed_position, type, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
} else {
if (paintable.hit_test(transformed_position, type, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
}
if (paintable_box.stacking_context()) {
if (z_index.value_or(0) == 0) {
if (paintable_box.stacking_context()->hit_test(transformed_position, type, callback) == TraversalDecision::Break) {
should_exit = true;
return TraversalDecision::Break;
}
}
}
return TraversalDecision::Continue;
});
if (should_exit)
return TraversalDecision::Break;
}
// 5. the in-flow, inline-level, non-positioned descendants, including inline tables and inline blocks.
if (paintable().layout_node().children_are_inline() && is<Layout::BlockContainer>(paintable().layout_node())) {
@ -434,23 +383,10 @@ TraversalDecision StackingContext::hit_test(CSSPixelPoint position, HitTestType
}
// 4. the non-positioned floats.
for_each_in_subtree_within_same_stacking_context_in_reverse(paintable(), [&](Paintable const& paintable) {
VERIFY(!should_exit);
if (!paintable.is_paintable_box())
return TraversalDecision::Continue;
auto const& paintable_box = verify_cast<PaintableBox>(paintable);
if (paintable_box.is_floating()) {
if (paintable_box.hit_test(transformed_position, type, callback) == TraversalDecision::Break) {
should_exit = true;
return TraversalDecision::Break;
}
}
return TraversalDecision::Continue;
});
if (should_exit)
return TraversalDecision::Break;
for (auto const& paintable : m_non_positioned_floating_descendants.in_reverse()) {
if (paintable.hit_test(transformed_position, type, callback) == TraversalDecision::Break)
return TraversalDecision::Break;
}
// 3. the in-flow, non-inline-level, non-positioned descendants.
if (!paintable().layout_node().children_are_inline()) {