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LibWeb: Use offset of nearest scrollable ancestor for positioned boxes

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Because positioned descendants are painted out-of-order we need to
separately apply offset of nearest scrollable box for them.

Fixes https://github.com/SerenityOS/serenity/issues/20554
This commit is contained in:
Aliaksandr Kalenik 2023-12-11 16:57:47 +01:00 • committed by Andreas Kling
parent 2952f01e84
commit 6b79508c08
5 changed files with 167 additions and 0 deletions
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10
Userland/Libraries/LibWeb/Painting/StackingContext.cpp
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@ -226,6 +226,13 @@ void StackingContext::paint_internal(PaintContext& context) const
: TraversalDecision::Continue;
}
// Apply scroll offset of nearest scrollable ancestor before painting the positioned descendant.
PaintableBox const* nearest_scrollable_ancestor = nullptr;
if (paintable.is_paintable_box())
nearest_scrollable_ancestor = static_cast<PaintableBox const&>(paintable).nearest_scrollable_ancestor();
if (nearest_scrollable_ancestor)
nearest_scrollable_ancestor->apply_scroll_offset(context, PaintPhase::Foreground);
// At this point, `paintable_box` is a positioned descendant with z-index: auto.
// FIXME: This is basically duplicating logic found elsewhere in this same function. Find a way to make this more elegant.
auto exit_decision = TraversalDecision::Continue;
@ -247,6 +254,9 @@ void StackingContext::paint_internal(PaintContext& context) const
if (containing_block_paintable)
containing_block_paintable->clear_clip_overflow_rect(context, PaintPhase::Foreground);
if (nearest_scrollable_ancestor)
nearest_scrollable_ancestor->reset_scroll_offset(context, PaintPhase::Foreground);
return exit_decision;
});