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LibWeb: Implement document.elementFromPoint()

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This function uses our existing hit testing code to determine the
topmost element at the given coordinates relative to the viewport.
This commit is contained in:
Tim Ledbetter 2024-02-06 06:02:51 +00:00 • committed by Andreas Kling
parent c732e03ea0
commit 69df94ec5c
5 changed files with 75 additions and 0 deletions
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5
Tests/LibWeb/Text/expected/DOM/Element-from-point.txt Normal file
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@ -0,0 +1,5 @@
Negative coordinates return null: true
Coordinates outside the viewport return null: true
<HTML id="root-element" >
<DIV id="large-box" >
<DIV id="small-box" >

33
Tests/LibWeb/Text/input/DOM/Element-from-point.html Normal file
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@ -0,0 +1,33 @@
<!DOCTYPE html>
<html id="root-element">
<style>
#large-box {
position: absolute;
top: 10px;
left: 500px;
width: 100px;
height: 100px;
background-color: magenta;
}
#small-box {
position: absolute;
top: 35px;
left: 525px;
width: 50px;
height: 50px;
background-color: yellow;
}
</style>
<script src="../include.js"></script>
<div id="large-box"></div><div id="small-box"></div>
<script>
test(() => {
println(`Negative coordinates return null: ${document.elementFromPoint(-1, -1) === null}`);
println(`Coordinates outside the viewport return null: ${document.elementFromPoint(99999, 99999) === null}`);
printElement(document.elementFromPoint(0, 0));
printElement(document.elementFromPoint(500, 10));
printElement(document.elementFromPoint(550, 60));
});
</script>
</html>

32
Userland/Libraries/LibWeb/DOM/Document.cpp
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@ -3721,4 +3721,36 @@ void Document::remove_form_associated_element_with_form_attribute(HTML::FormAsso
});
}
// https://drafts.csswg.org/cssom-view/#dom-document-elementfrompoint
Element const* Document::element_from_point(double x, double y)
{
// 1. If either argument is negative, x is greater than the viewport width excluding the size of a rendered scroll
// bar (if any), or y is greater than the viewport height excluding the size of a rendered scroll bar (if any), or
// there is no viewport associated with the document, return null and terminate these steps.
auto viewport_rect = this->viewport_rect();
CSSPixelPoint position { x, y };
// FIXME: This should account for the size of the scroll bar.
if (x < 0 || y < 0 || position.x() > viewport_rect.width() || position.y() > viewport_rect.height())
return nullptr;
// Ensure the layout tree exists prior to hit testing.
update_layout();
// 2. If there is a box in the viewport that would be a target for hit testing at coordinates x,y, when applying the transforms
// that apply to the descendants of the viewport, return the associated element and terminate these steps.
if (auto const* paintable_box = this->paintable_box(); paintable_box) {
if (auto result = paintable_box->hit_test(position, Painting::HitTestType::Exact); result.has_value()) {
if (auto* dom_node = result->dom_node(); dom_node && dom_node->is_element())
return static_cast<Element const*>(dom_node);
}
}
// 3. If the document has a root element, return the root element and terminate these steps.
if (auto const* document_root_element = first_child_of_type<Element>(); document_root_element)
return document_root_element;
// 4. Return null.
return nullptr;
}
}

2
Userland/Libraries/LibWeb/DOM/Document.h
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@ -560,6 +560,8 @@ public:
void add_form_associated_element_with_form_attribute(HTML::FormAssociatedElement&);
void remove_form_associated_element_with_form_attribute(HTML::FormAssociatedElement&);
Element const* element_from_point(double x, double y);
protected:
virtual void initialize(JS::Realm&) override;
virtual void visit_edges(Cell::Visitor&) override;

3
Userland/Libraries/LibWeb/DOM/Document.idl
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@ -116,6 +116,9 @@ interface Document : Node {
// https://www.w3.org/TR/web-animations-1/#extensions-to-the-document-interface
readonly attribute DocumentTimeline timeline;
// https://drafts.csswg.org/cssom-view/#extensions-to-the-document-interface
Element? elementFromPoint(double x, double y);
};
dictionary ElementCreationOptions {