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LibWeb: Optimize stacking context rebuilds on opacity change

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Stacking context tree rebuild can be avoided if opacity value changes
within the range below 1.
This commit is contained in:
Aliaksandr Kalenik 2023-07-29 17:28:14 +02:00 • committed by Andreas Kling
parent b5a728ae5f
commit 921aee8c66
1 changed files with 12 additions and 1 deletions
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13
Userland/Libraries/LibWeb/DOM/Element.cpp
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@ -15,6 +15,7 @@
#include <LibWeb/CSS/ResolvedCSSStyleDeclaration.h>
#include <LibWeb/CSS/SelectorEngine.h>
#include <LibWeb/CSS/StyleComputer.h>
#include <LibWeb/CSS/StyleValues/NumberStyleValue.h>
#include <LibWeb/DOM/Attr.h>
#include <LibWeb/DOM/DOMTokenList.h>
#include <LibWeb/DOM/Document.h>
@ -420,8 +421,18 @@ static Element::RequiredInvalidationAfterStyleChange compute_required_invalidati
} else if (CSS::property_affects_layout(property_id)) {
invalidation.relayout = true;
}
if (CSS::property_affects_stacking_context(property_id))
if (property_id == CSS::PropertyID::Opacity) {
// OPTIMIZATION: An element creates a stacking context when its opacity changes from 1 to less than 1
// and stops to create one when opacity returns to 1. So stacking context tree rebuild is
// not required for opacity changes within the range below 1.
auto old_value_opacity = old_value.has_value() ? old_value->style->as_number().number() : 1;
auto new_value_opacity = new_value.has_value() ? new_value->style->as_number().number() : 1;
if (old_value_opacity != new_value_opacity && (old_value_opacity == 1 || new_value_opacity == 1)) {
invalidation.rebuild_stacking_context_tree = true;
}
} else if (CSS::property_affects_stacking_context(property_id)) {
invalidation.rebuild_stacking_context_tree = true;
}
invalidation.repaint = true;
}
return invalidation;