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LibWeb: Implement :nth-child pseudo-class

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miere43 2021-05-08 23:19:25 +03:00 • committed by Andreas Kling
parent 1e0e8b27c0
commit aa83539d7b
6 changed files with 161 additions and 36 deletions
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47
Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp
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@ -82,6 +82,53 @@ static bool matches(const CSS::Selector::SimpleSelector& component, const DOM::E
return false;
}
break;
case CSS::Selector::SimpleSelector::PseudoClass::NthChild:
const auto step_size = component.nth_child_pattern.step_size;
const auto offset = component.nth_child_pattern.offset;
if (step_size == 0 && offset == 0)
return false; // "If both a and b are equal to zero, the pseudo-class represents no element in the document tree."
const auto* parent = element.parent_element();
if (!parent)
return false;
int index = 1;
for (auto* child = parent->first_child_of_type<DOM::Element>(); child && child != &element; child = child->next_element_sibling()) {
++index;
}
if (step_size < 0) {
// When "step_size" is negative, selector represents first "offset" elements in document tree.
if (offset <= 0 || index > offset)
return false;
else
break;
} else if (step_size == 1) {
// When "step_size == 1", selector represents last "offset" elements in document tree.
if (offset < 0 || index < offset)
return false;
else
break;
}
// Like "a % b", but handles negative integers correctly.
const auto canonical_modulo = [](int a, int b) -> int {
int c = a % b;
if ((c < 0 && b > 0) || (c > 0 && b < 0)) {
c += b;
}
return c;
};
if (step_size == 0) {
// Avoid divide by zero.
if (index != offset) {
return false;
}
} else if (canonical_modulo(index - offset, step_size) != 0) {
return false;
}
break;
}
switch (component.attribute_match_type) {