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LibWeb: Avoid layout invalidation for some CSS property changes

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Use the new CSS::property_affects_layout() helper to figure out if we
actually need to perform a full relayout after recomputing style.

There are three tiers of required invalidation after an element receives
new style: none, repaint only, or full relayout.

This avoids the need to rebuild the layout tree (and perform layout on
it) when trivial properties like "color" etc are changed.
This commit is contained in:
Andreas Kling 2022-03-16 17:48:50 +01:00
parent 275db39c94
commit f1711a562a
3 changed files with 60 additions and 10 deletions
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48
Userland/Libraries/LibWeb/DOM/Element.cpp
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@ -267,18 +267,60 @@ void Element::parse_attribute(const FlyString& name, const String& value)
}
}
void Element::recompute_style()
enum class RequiredInvalidation {
None,
RepaintOnly,
Relayout,
};
static RequiredInvalidation compute_required_invalidation(CSS::StyleProperties const& old_style, CSS::StyleProperties const& new_style)
{
bool requires_repaint = false;
for (auto i = to_underlying(CSS::first_property_id); i <= to_underlying(CSS::last_property_id); ++i) {
auto property_id = static_cast<CSS::PropertyID>(i);
auto const& old_value = old_style.properties()[i];
auto const& new_value = new_style.properties()[i];
if (!old_value && !new_value)
continue;
if (!old_value || !new_value)
return RequiredInvalidation::Relayout;
if (*old_value == *new_value)
continue;
if (CSS::property_affects_layout(property_id))
return RequiredInvalidation::Relayout;
requires_repaint = true;
}
if (requires_repaint)
return RequiredInvalidation::RepaintOnly;
return RequiredInvalidation::None;
}
Element::NeedsRelayout Element::recompute_style()
{
set_needs_style_update(false);
VERIFY(parent());
auto new_computed_css_values = document().style_computer().compute_style(*this);
if (m_computed_css_values && *m_computed_css_values == *new_computed_css_values)
return;
auto required_invalidation = RequiredInvalidation::Relayout;
if (m_computed_css_values)
required_invalidation = compute_required_invalidation(*m_computed_css_values, *new_computed_css_values);
if (required_invalidation == RequiredInvalidation::None)
return NeedsRelayout::No;
m_computed_css_values = move(new_computed_css_values);
if (required_invalidation == RequiredInvalidation::RepaintOnly && layout_node()) {
layout_node()->apply_style(*m_computed_css_values);
layout_node()->set_needs_display();
return NeedsRelayout::No;
}
// FIXME: Get rid of this layout invalidation and let Document take care of it.
// There seems to be some missing invalidation somewhere else that this is papering over.
document().invalidate_layout();
return NeedsRelayout::Yes;
}
NonnullRefPtr<CSS::StyleProperties> Element::resolved_css_values()