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LibWeb: Lazily obtain the Z-index for children in StackingContext

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In `StackingContext::paint_descendants()`, we don't need to obtain the
computed values nor the Z-index of a child unless certain other
conditions are true. Let these conditions short-circuit before actually
reaching into the computed values, which shows up in profiles.
This commit is contained in:
Jelle Raaijmakers 2025-06-16 16:51:47 +02:00 • committed by Jelle Raaijmakers
commit ade5709939
Notes: github-actions[bot] 2025-06-17 09:56:52 +00:00
1 changed files with 5 additions and 7 deletions
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12
Libraries/LibWeb/Painting/StackingContext.cpp
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@ -2,6 +2,7 @@
* Copyright (c) 2020-2022, Andreas Kling <andreas@ladybird.org>
* Copyright (c) 2022, Sam Atkins <atkinssj@serenityos.org>
* Copyright (c) 2024, Aliaksandr Kalenik <kalenik.aliaksandr@gmail.com>
* Copyright (c) 2025, Jelle Raaijmakers <jelle@ladybird.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -113,8 +114,6 @@ void StackingContext::paint_descendants(PaintContext& context, Paintable const&
paintable.before_children_paint(context, to_paint_phase(phase));
paintable.for_each_child([&context, phase](auto& child) {
auto const& z_index = child.computed_values().z_index();
if (child.layout_node().is_svg_svg_box()) {
paint_svg(context, static_cast<PaintableBox const&>(child), to_paint_phase(phase));
return IterationDecision::Continue;
@ -128,8 +127,8 @@ void StackingContext::paint_descendants(PaintContext& context, Paintable const&
// "For each one of these, treat the element as if it created a new stacking context, but any positioned
// descendants and descendants which actually create a new stacking context should be considered part of
// the parent stacking context, not this new one."
auto grid_item_should_be_treated_as_stacking_context = child.layout_node().is_grid_item() && !z_index.has_value();
if (grid_item_should_be_treated_as_stacking_context) {
auto const& z_index = [&] { return child.computed_values().z_index(); };
if (child.layout_node().is_grid_item() && !z_index().has_value()) {
// FIXME: This may not be fully correct with respect to the paint phases.
if (phase == StackingContextPaintPhase::Foreground)
paint_node_as_stacking_context(child, context);
@ -141,15 +140,14 @@ void StackingContext::paint_descendants(PaintContext& context, Paintable const&
// element as if it created a new stacking context, but any positioned descendants and
// descendants which actually create a new stacking context should be considered part of the
// parent stacking context, not this new one.
auto floating_item_should_be_treated_as_stacking_context = child.is_floating() && !child.is_positioned() && !z_index.has_value();
if (floating_item_should_be_treated_as_stacking_context) {
if (child.is_floating() && !child.is_positioned() && !z_index().has_value()) {
if (phase == StackingContextPaintPhase::Floats) {
paint_node_as_stacking_context(child, context);
}
return IterationDecision::Continue;
}
if (child.is_positioned() && z_index.value_or(0) == 0)
if (child.is_positioned() && z_index().value_or(0) == 0)
return IterationDecision::Continue;
bool child_is_inline_or_replaced = child.is_inline() || is<Layout::ReplacedBox>(child.layout_node());