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LibWeb: Add paint containment clipping

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The contain-paint-stacking-context-001a.html test has been removed
for now because it has a 1px tall blue line at the top that should
not be there. With paint containment, this line is removed only in
the actual test case, but not in the reference. This is because of
the font that we use in testing and happens in Chromium as well if
the test is run with that font.
This commit is contained in:
Psychpsyo 2025-05-03 11:46:39 +02:00 • committed by Alexander Kalenik
commit 4989c5c793
Notes: github-actions[bot] 2025-05-13 12:32:31 +00:00
4 changed files with 84 additions and 67 deletions
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20
Libraries/LibWeb/Painting/ViewportPaintable.cpp
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@ -129,7 +129,8 @@ void ViewportPaintable::assign_clip_frames()
auto overflow_y = paintable_box.computed_values().overflow_y();
// Note: Overflow may be clip on one axis and visible on the other.
auto has_hidden_overflow = overflow_x != CSS::Overflow::Visible || overflow_y != CSS::Overflow::Visible;
if (has_hidden_overflow || paintable_box.get_clip_rect().has_value()) {
auto element = as_if<DOM::Element>(paintable_box.layout_node().dom_node());
if (has_hidden_overflow || paintable_box.get_clip_rect().has_value() || (element && element->has_paint_containment())) {
auto clip_frame = adopt_ref(*new ClipFrame());
clip_state.set(paintable_box, move(clip_frame));
}
@ -177,6 +178,23 @@ void ViewportPaintable::assign_clip_frames()
clip_y = true;
}
// https://drafts.csswg.org/css-contain-2/#paint-containment
// 1. The contents of the element including any ink or scrollable overflow must be clipped to the overflow clip
// edge of the paint containment box, taking corner clipping into account. This does not include the creation of
// any mechanism to access or indicate the presence of the clipped content; nor does it inhibit the creation of
// any such mechanism through other properties, such as overflow, resize, or text-overflow.
// NOTE: This clipping shape respects overflow-clip-margin, allowing an element with paint containment
// to still slightly overflow its normal bounds.
if (auto element = as_if<DOM::Element>(block->dom_node())) {
if (element->has_paint_containment()) {
// NOTE: Note: The behavior is described in this paragraph is equivalent to changing 'overflow-x: visible' into
// 'overflow-x: clip' and 'overflow-y: visible' into 'overflow-y: clip' at used value time, while leaving other
// values of 'overflow-x' and 'overflow-y' unchanged.
clip_x = true;
clip_y = true;
}
}
if (clip_x || clip_y) {
// https://drafts.csswg.org/css-overflow-3/#corner-clipping
// As mentioned in CSS Backgrounds 3 § 4.3 Corner Clipping, the clipping region established by overflow can be