[IntersectionObserver] Implement intersection logic for the explicit root case

[Ali Juma]

Implement logic to compute the intersection of the target and root, for the case where the observer has a root element.

[Ali Juma]

Created attachment 347684 [details]
Patch

[Ali Juma]

Comment on attachment 347684 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=347684&action=review

> LayoutTests/imported/w3c/web-platform-tests/intersection-observer/containing-block-expected.txt:3
> +FAIL In containing block and intersecting. assert_equals: entries[0].boundingClientRect.top expected 18 but got 258

This fails because layout hasn't been updated when the intersection observation is computed. This will be fixed once observations are deferred until after layout.

> LayoutTests/imported/w3c/web-platform-tests/intersection-observer/isIntersecting-change-events-expected.txt:3
> +FAIL Rects in initial notifications should report initial positions. assert_equals: entries[2].target.isIntersecting equals true expected true but got false

This fails because entries[2] is case involving zero-area intersection, which isn't implemented yet.

[Simon Fraser (smfr)]

Comment on attachment 347684 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=347684&action=review

> Source/WebCore/dom/Document.cpp:7443
> +static void computeIntersectionObservation(IntersectionObserver& observer, Element* target, FloatRect& absTargetRect, FloatRect& absIntersectionRect, FloatRect& absRootBounds)

I'm not a big fan of the name. Maybe just computeIntersections() or computeIntersectionRects()? Make target an Element& since you don't null-check it.

> Source/WebCore/dom/Document.cpp:7454
> +    RenderBlock* rootRenderer = downcast<RenderBlock>(observer.root()->renderer());

Blank line above this please.

> Source/WebCore/dom/Document.cpp:7485
> +    absTargetRect = targetRenderer->localToAbsoluteQuad(FloatRect(localTargetBounds)).boundingBox();
> +    absRootBounds = rootRenderer->localToAbsoluteQuad(localRootBounds).boundingBox();

It's a shame that these two localToAbsoluteQuad() calls will both pay the cost of traversing the common ancestors of 'target' and 'root'. Not worth optimizing now, though.

[Ali Juma]

Created attachment 347712 [details]
Patch for landing

[WebKit Commit Bot]

Comment on attachment 347712 [details]
Patch for landing

Clearing flags on attachment: 347712

Committed r235358: <https://trac.webkit.org/changeset/235358>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/43749632>