62c3a5c918
The display list builder only categorized direct children into CSS paint-order buckets. Stacking-context elements nested inside normal-flow intermediaries (like <body>) rendered in document order instead of at the correct steps 2/7 per CSS 2.1 Appendix E. This caused elements with explicit z-index to paint incorrectly relative to siblings. Add a recursive tree walk (collect_stacking_participants) that collects stacking-context descendants from the entire subtree, tracking ancestor overflow:hidden clip rects. Hoisted elements render with preserved clips via render_with_ancestor_clips. Skip guards in render_layout_box_normal and render_non_inline_descendants prevent double-rendering. Scope is limited to stacking contexts (positioned + z-index) to avoid regressions with float paint ordering. Positioned-auto deep hoisting and stacking contexts inside floats are documented follow-ups. Promotes 4 WPT tests, demotes 1 (pre-existing step 3/5 limitation). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
34 lines
880 B
HTML
34 lines
880 B
HTML
<!DOCTYPE html>
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<html>
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<head>
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<style>
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body {
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margin: 0;
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}
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.fixed-bg {
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position: fixed;
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top: 0;
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left: 0;
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width: 200px;
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height: 100px;
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background-color: red;
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/* z-index: auto (no stacking context) */
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}
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.relative-fg {
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position: relative;
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z-index: 2;
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width: 200px;
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height: 100px;
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background-color: green;
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}
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</style>
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</head>
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<body>
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<!-- fixed-bg is a direct child of body, positioned with z-index auto -->
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<div class="fixed-bg"></div>
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<!-- relative-fg is also a direct child of body, creates stacking context with z-index:2 -->
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<!-- It should paint ON TOP of fixed-bg because z-index:2 > z-index:auto -->
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<div class="relative-fg"></div>
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</body>
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</html>
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