NEW 297033
[css-anchor-position-1] Changing window focus causes relayout on anchor() tests 
https://bugs.webkit.org/show_bug.cgi?id=297033
Summary [css-anchor-position-1] Changing window focus causes relayout on anchor() tests
fantasai
Reported 2025-08-06 20:04:18 PDT
For some reason, we are triggering relayout when the window changes focus on anchor positioning tests such as https://wpt.live/css/css-anchor-position/anchor-scope-scroll.html This is noticeable if you turn on logging. Seems like an excessive amount of work given nothing is supposed to change?
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Radar WebKit Bug Importer
Comment 1 2025-08-06 20:04:26 PDT
<rdar://problem/157715763>
alan
Comment 2 2025-08-06 20:10:18 PDT
It looks like the anchored element's inset value goes from fixed to auto on window focus (which then triggers layout). in RenderStyle::changeRequiresLayout (lldb) expr a.m_sides[0] (const std::array<WebCore::Style::InsetEdge, 4>::value_type) $5 = { WebCore::Style::LengthWrapperBase<WebCore::Style::LengthPercentage<WebCore::CSS::Range, float>, WebCore::Constant<WebCore::CSSValueAuto> > = { m_value = { = (m_intValue = 1126105088, m_floatValue = 159, m_calculationValueHandle = 1126105088) m_type = Fixed m_hasQuirk = false m_isFloat = true m_isEmptyValue = false } } } (lldb) expr b.m_sides[0] (const std::array<WebCore::Style::InsetEdge, 4>::value_type) $6 = { WebCore::Style::LengthWrapperBase<WebCore::Style::LengthPercentage<WebCore::CSS::Range, float>, WebCore::Constant<WebCore::CSSValueAuto> > = { m_value = { = (m_intValue = 0, m_floatValue = 0, m_calculationValueHandle = 0) m_type = Auto m_hasQuirk = false m_isFloat = true m_isEmptyValue = false } } }
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