Bug 272280 – Avoid over-eager clipping of child layers in multicolumn

• Component: Layout and Rendering
• Status: RESOLVED FIXED

[Ahmad Saleem]

Hi Team,

While going through Blink's commit, I came across another failing test:

Test Case: https://jsfiddle.net/z8d5auqe/show

^ Safari 17.4.1 fails it while Chrome Canary 125 and Firefox Nightly 126 matches each other.

Blink Commit: https://chromium.googlesource.com/chromium/src.git/+/e500cbd3ba36bf3216087481790f5aece0e778a5

WebKit Source: https://searchfox.org/wubkat/source/Source/WebCore/rendering/RenderFragmentContainer.cpp#154

___

This compiles and fix this above test case:

LayoutRect RenderFragmentContainer::overflowRectForFragmentedFlowPortion(const LayoutRect& fragmentedFlowPortionRect, bool isFirstPortion, bool isLastPortion) const
{
    ASSERT(isValid());
    // Only clip along the block direction axis.
    LayoutRect clipRect(LayoutRect::infiniteRect());

    if (m_fragmentedFlow->isHorizontalWritingMode()) {
        if (!isFirstPortion)
            clipRect.shiftYEdgeTo(fragmentedFlowPortionRect.y());
        if (!isLastPortion)
            clipRect.shiftMaxYEdgeTo(fragmentedFlowPortionRect.maxY());
        return clipRect;
    }

    if (!isFirstPortion)
        clipRect.shiftYEdgeTo(fragmentedFlowPortionRect.x());
    if (!isLastPortion)
        clipRect.shiftMaxYEdgeTo(fragmentedFlowPortionRect.maxX());
    return clipRect;
}

_____

NOTE - I have ran both 'WPT' (CSS-Contain) and (CSS-MULTICOL) and no progression and regressions.

Just raising so we can track and fix it.

Thanks!

[Radar WebKit Bug Importer]

<rdar://problem/126413036>

[Ahmad Saleem]

Correct one:

LayoutRect RenderFragmentContainer::overflowRectForFragmentedFlowPortion(const LayoutRect& fragmentedFlowPortionRect, bool isFirstPortion, bool isLastPortion) const
{
    ASSERT(isValid());
    // Only clip along the block direction axis.
    LayoutRect clipRect(LayoutRect::infiniteRect());

    if (m_fragmentedFlow->isHorizontalWritingMode()) {
        if (!isFirstPortion)
            clipRect.shiftYEdgeTo(fragmentedFlowPortionRect.y());
        if (!isLastPortion)
            clipRect.shiftMaxYEdgeTo(fragmentedFlowPortionRect.maxY());
        return clipRect;
    }

    if (!isFirstPortion)
        clipRect.shiftXEdgeTo(fragmentedFlowPortionRect.x());
    if (!isLastPortion)
        clipRect.shiftMaxXEdgeTo(fragmentedFlowPortionRect.maxX());
    return clipRect;
}

___

It leads to following legit WPT failure:

css/css-break/out-of-flow-in-multicolumn-018.htm

while also progression (one) here:

css/css-break/relpos-inline-hit-testing.html

Additionally, just 0.01% difference here:

unbreakable-block-too-tall-at-column-start.html

___

PR Attempt - https://github.com/WebKit/WebKit/pull/26993

[Ahmad Saleem]

Pull request: https://github.com/WebKit/WebKit/pull/47276

[EWS]

Committed 302249@main (1ff6d9ccac00): <https://commits.webkit.org/302249@main>

Reviewed commits have been landed. Closing PR #47276 and removing active labels.