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LibWeb: Fix scroll state refresh in cached display list for iframes

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6507d23 introduced a bug when snapshot for iframe is saved in
`PaintNestedDisplayList` and, since display lists are immutable, it's
not possible to update before the next repaint.

This change fixes the issue by moving `ScrollStateSnapshot` for
nested display lists from `PaintNestedDisplayList` to
`HashMap<NonnullRefPtr<DisplayList>, ScrollStateSnapshot>` that is
placed into pending rendering task, making it possible to update
snapshots for all display lists before the next repaint.

This change doesn't have a test because it's really hard to make a ref
test that will specifically check scenario when scroll offset of an
iframe is advanced after display list is cached. We already have
`Tests/LibWeb/Ref/input/scroll-iframe.html` but unfortunately it did
not catch this bug.

Fixes https://github.com/LadybirdBrowser/ladybird/issues/5486
This commit is contained in:
Aliaksandr Kalenik 2025-07-25 01:39:31 +02:00 • committed by Alexander Kalenik
commit 8569124b87
Notes: github-actions[bot] 2025-07-26 15:54:30 +00:00
18 changed files with 63 additions and 28 deletions
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28
Libraries/LibWeb/HTML/Navigable.cpp
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@ -46,6 +46,7 @@
#include <LibWeb/Loader/GeneratedPagesLoader.h>
#include <LibWeb/Page/Page.h>
#include <LibWeb/Painting/DisplayListPlayerSkia.h>
#include <LibWeb/Painting/NavigableContainerViewportPaintable.h>
#include <LibWeb/Painting/Paintable.h>
#include <LibWeb/Painting/ViewportPaintable.h>
#include <LibWeb/Platform/EventLoopPlugin.h>
@ -2612,14 +2613,35 @@ void Navigable::start_display_list_rendering(Gfx::PaintingSurface& painting_surf
callback();
return;
}
document->paintable()->refresh_scroll_state();
auto display_list = document->record_display_list(paint_config);
if (!display_list) {
callback();
return;
}
auto scroll_state_snapshot = document->paintable()->scroll_state().snapshot();
m_rendering_thread.enqueue_rendering_task(*display_list, move(scroll_state_snapshot), painting_surface, move(callback));
auto& document_paintable = *document->paintable();
Painting::ScrollStateSnapshotByDisplayList scroll_state_snapshot_by_display_list;
document_paintable.refresh_scroll_state();
auto scroll_state_snapshot = document_paintable.scroll_state().snapshot();
scroll_state_snapshot_by_display_list.set(*display_list, move(scroll_state_snapshot));
// Collect scroll state snapshots for each nested navigable
document_paintable.for_each_in_inclusive_subtree_of_type<Painting::NavigableContainerViewportPaintable>([&scroll_state_snapshot_by_display_list](auto& navigable_container_paintable) {
auto const* hosted_document = navigable_container_paintable.layout_box().dom_node().content_document_without_origin_check();
if (!hosted_document || !hosted_document->paintable())
return TraversalDecision::Continue;
// We are only interested in collecting scroll state snapshots for visible nested navigables, which is
// detectable by checking if they have a cached display list that should've been populated by
// record_display_list() on top-level document.
auto navigable_display_list = hosted_document->cached_display_list();
if (!navigable_display_list)
return TraversalDecision::Continue;
const_cast<DOM::Document&>(*hosted_document).paintable()->refresh_scroll_state();
auto navigable_scroll_state_snapshot = hosted_document->paintable()->scroll_state().snapshot();
scroll_state_snapshot_by_display_list.set(*navigable_display_list, move(navigable_scroll_state_snapshot));
return TraversalDecision::Continue;
});
m_rendering_thread.enqueue_rendering_task(*display_list, move(scroll_state_snapshot_by_display_list), painting_surface, move(callback));
}
RefPtr<Gfx::SkiaBackendContext> Navigable::skia_backend_context() const