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LibWeb: Extract shared lazy-loading behavior into a base class

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`<iframe>` and `<img>` tags share the same spec for several aspects of
lazy-loading: how the `loading` attribute works, the "will lazy load
element" steps, and a member for storing the lazy-load resumption
steps. So let's share the implementation by using a base class.

This mostly involves moving things around. However, we also change the
`start_intersection_observing_a_lazy_loading_element()` method to take
a LazyLoadingElement, and operate on one, instead of always casting to
HTMLImageElement.

We do unfortunately have to do some shenanigans to make the cast work,
by adding a virtual function stub in DOM::Element.
This commit is contained in:
Sam Atkins 2023-11-21 18:50:09 +00:00 • committed by Andreas Kling
parent cc2008ea0d
commit cc633123ca
Notes: sideshowbarker 2024-07-17 08:27:05 +09:00
7 changed files with 111 additions and 56 deletions
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43
Userland/Libraries/LibWeb/HTML/HTMLImageElement.cpp
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@ -71,7 +71,7 @@ void HTMLImageElement::visit_edges(Cell::Visitor& visitor)
Base::visit_edges(visitor);
visitor.visit(m_current_request);
visitor.visit(m_pending_request);
visitor.visit(m_lazy_load_resumption_steps);
visit_lazy_loading_element(visitor);
}
void HTMLImageElement::apply_presentational_hints(CSS::StyleProperties& style) const
@ -165,11 +165,6 @@ void HTMLImageElement::set_visible_in_viewport(bool)
// FIXME: Loosen grip on image data when it's not visible, e.g via volatile memory.
}
void HTMLImageElement::set_lazy_load_resumption_steps(Function<void()> steps)
{
m_lazy_load_resumption_steps = JS::create_heap_function(vm().heap(), move(steps));
}
// https://html.spec.whatwg.org/multipage/embedded-content.html#dom-img-width
unsigned HTMLImageElement::width() const
{
@ -528,7 +523,7 @@ after_step_7:
m_pending_request = image_request;
// 23. Let delay load event be true if the img's lazy loading attribute is in the Eager state, or if scripting is disabled for the img, and false otherwise.
auto delay_load_event = lazy_loading() == LazyLoading::Eager;
auto delay_load_event = lazy_loading_attribute() == LazyLoading::Eager;
// When delay load event is true, fetching the image must delay the load event of the element's node document
// until the task that is queued by the networking task source once the resource has been fetched (defined below) has been run.
@ -558,7 +553,7 @@ after_step_7:
// FIXME: 22. Set request's priority to the current state of the element's fetchpriority attribute.
// 24. If the will lazy load element steps given the img return true, then:
if (will_lazy_load()) {
if (will_lazy_load_element()) {
// 1. Set the img's lazy load resumption steps to the rest of this algorithm starting with the step labeled fetch the image.
set_lazy_load_resumption_steps([this, request, image_request]() {
image_request->fetch_image(realm(), request);
@ -1008,36 +1003,4 @@ void HTMLImageElement::animate()
layout_node()->set_needs_display();
}
// https://html.spec.whatwg.org/multipage/urls-and-fetching.html#lazy-loading-attributes
HTMLImageElement::LazyLoading HTMLImageElement::lazy_loading() const
{
auto value = deprecated_attribute(HTML::AttributeNames::loading);
if (value.equals_ignoring_ascii_case("lazy"sv))
return LazyLoading::Lazy;
return LazyLoading::Eager;
}
// https://html.spec.whatwg.org/multipage/urls-and-fetching.html#will-lazy-load-element-steps
bool HTMLImageElement::will_lazy_load() const
{
// 1. If scripting is disabled for element, then return false.
// Spec Note: This is an anti-tracking measure, because if a user agent supported lazy loading when scripting is
// disabled, it would still be possible for a site to track a user's approximate scroll position throughout
// a session, by strategically placing images in a page's markup such that a server can track how many
// images are requested and when.
if (is_scripting_disabled())
return false;
// 2. If element's lazy loading attribute is in the Lazy state, then return true.
// 3. Return false.
return lazy_loading() == LazyLoading::Lazy;
}
JS::GCPtr<JS::HeapFunction<void()>> HTMLImageElement::take_lazy_load_resumption_steps(Badge<DOM::Document>)
{
auto lazy_load_resumption_steps = m_lazy_load_resumption_steps;
m_lazy_load_resumption_steps = nullptr;
return lazy_load_resumption_steps;
}
}