Re: [css-transforms] Interaction of transforms with scrollable area

On Sat, Jan 9, 2016 at 2:30 AM Robert O'Callahan <robert@ocallahan.org>
wrote:

> Context: https://bugzilla.mozilla.org/show_bug.cgi?id=1236386
> https://bug1236386.bmoattachments.org/attachment.cgi?id=8703469
>
> This issue's probably already been discussed but I don't know where. The
> question is: how does a transformed element contribute to the scrollable
> area of an "overflow:auto/scroll" ancestor? For example, does its
> border-box before transformation contribute to the scrollable area?
>
> In the referenced testcase Chrome seems to say "no" if the transformed
> element is a direct child of the box, "yes" otherwise. Firefox says "yes,
> but only in the vertical direction". Edge says "yes". More testing would
> probably be worthwhile.
>

I dug into the code in Blink to figure out what it's doing, for further
background. The results you see are because of the following implementation
detail:

The scrolling area of an overflow-scrolling element is expanded to contain
the transformed size of a *direct* child. It is never contracted if the
transform makes the visual size of the child smaller than its original box.

Here is the WebKit bug <https://bugs.webkit.org/show_bug.cgi?id=47514>
leading to the implementation (It doesn't refer to direct children).

Chris



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