Bug 171140 – [iOS] REGRESSION (r209409): getBoundingClientRect is wrong for fixed-position elements in resize/orientationchange

• Status: RESOLVED
• Resolution: FIXED
• Component: Layout and Rendering

[Tim Horton]

Created attachment 307789 [details]
testcase

Steps to Reproduce:

1. Open attached test page in Safari on iOS 10.3+.
2. Rotate.

Expected: all three borders should line up
Actual: the borders (green and blue) that are derived from the bounding client rect of the fixed-position element inside onresize/onorientationchange don't line up with the fixed-position element's border.

[Radar WebKit Bug Importer]

<rdar://problem/31765167>

[Simon Fraser (smfr)]

We need a way to test rotation.

[Tim Horton]

I don't think testing this is blocked on "a way to test rotation", I'm pretty sure this is just a resize bug. And we have ways to test that.

[Tim Horton]

This regressed in https://trac.webkit.org/changeset/209409/webkit.

[Tim Horton]

(And ToT is OK with Visual Viewports disabled)

[Tim Horton]

It turns out (after hours of debugging) that the problem here is simple: WebPage::dynamicViewportSizeUpdate was not updated to set the layoutViewportOverrideRect instead of the customFixedPositionLayoutRect like WebPage::updateVisibleContentRects was.

I have tested after making this change and things are better; I'll make some tests and post a patch.

[Tim Horton]

Created attachment 308144 [details]
Patch

[Tim Horton]

Comment on attachment 308144 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=308144&action=review

> Source/WebKit2/WebProcess/WebPage/ios/WebPageIOS.mm:-2992
> -    frameView.setCustomFixedPositionLayoutRect(fixedPositionLayoutRect);

We may want to try to clean this up and share more code between dynamicViewportSizeUpdate and updateVisibleContentRects, but that is a much bigger change that I don't want to make at the moment.

[Simon Fraser (smfr)]

Comment on attachment 308144 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=308144&action=review

> Source/WebKit2/WebProcess/WebPage/ios/WebPageIOS.mm:2994
> +        frameView.setLayoutViewportOverrideRect(LayoutRect(fixedPositionLayoutRect));

This is wrong, because fixedPositionLayoutRect comes from frameView.viewportConstrainedObjectsRect(), which is for the old-style fixed behavior, not the visual viewport behavior. We need to get this rect from _page->computeCustomFixedPositionRect().

[Simon Fraser (smfr)]

Created attachment 309262 [details]
Patch for EWS

[Simon Fraser (smfr)]

Created attachment 309316 [details]
Patch

[Simon Fraser (smfr)]

Created attachment 309323 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 309323 [details]
Patch

Clearing flags on attachment: 309323

Committed r216352: <http://trac.webkit.org/changeset/216352>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.