942995 - APZC for overflow:hidden element should not allow panning

Status: RESOLVED FIXED

(Core :: Panning and Zooming, defect)

Description

[Botond Ballo [:botond]]

The RecordFrameMetrics call here:

http://mxr.mozilla.org/mozilla-central/source/layout/base/nsDisplayList.cpp#1186

unconditionally assigns a non-null scroll id to the root scroll frame of the root content document. With APZ enabled, this causes an APZC to be created for this frame.

If the element corresponding to the root scroll frame is overflow:hidden, this allows the user to scroll the overflow:hidden element by panning. This is undesirable.

Since there is no use in having APZC for an overflow:hidden element, we can solve this problem by getting rid of it in such a case (by assigning NULL_SCROLL_ID to the frame).

Comment 1

[Botond Ballo [:botond]]

Attachment: bug942995.patch

Comment 2

[Botond Ballo [:botond]]

After further discussion (see bug 940691), we don't want to go the route of not having an APZC for an overflow:hidden element, because we always want to have a root APZC. Instead, an APZC for an overflow:hidden element should disallow panning.

Comment 3

[Botond Ballo [:botond]]

Attachment: bug942995.patch

Reposting Kats' patch from bug 940691. Timothy, can you give it another round of feedback in light of our IRC conversation?

Comment 4

[Timothy Nikkel (:tnikkel)]

Comment on attachment 8339494 [details] [diff] [review]
bug942995.patch

This seems fine based on what I know now.

Comment 5

[Botond Ballo [:botond]]

Try push: https://tbpl.mozilla.org/?tree=Try&rev=6c920312c805 (also covers bug 942799).

Comment 6

[Botond Ballo [:botond]]

Comment on attachment 8339494 [details] [diff] [review]
bug942995.patch

(In reply to Botond Ballo [:botond] from comment #5)
> Try push: https://tbpl.mozilla.org/?tree=Try&rev=6c920312c805 (also covers
> bug 942799).

Looks clean. Flagging for review.

Comment 7

[Milan Sreckovic [:milan] (needinfo for best results)]

This one, together with the patch for bug 942799 takes care of most of the first wave of problems with APZC that I've seen.  The only one that I still see is in the gallery app (bug 944511)

Comment 8

[Botond Ballo [:botond]]

https://hg.mozilla.org/integration/b2g-inbound/rev/2139b34164d9

Comment 9

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/2139b34164d9

Comment 10

[Jim Mathies [:jimm]]

This broke touch scrolling in metro for top level frames. If there isn't an easy fix, we should back this out. Unfortunately it made it into this morning's nightly.