988991 - Able to pan an iframe that shouldn't be pannable

Status: RESOLVED DUPLICATE of bug 953239

(Firefox for Android Graveyard :: Toolbar, defect)

Description

[Kartikaya Gupta (email:[e-mail])]

STR:

1. Load the attached testcase (stolen from [1])
2. Pan the youtube thingy (works better when you pan on the left side of the black rect rather than the right side)

Expected:
Things shouldn't pan

Actual:
The iframe seems to pan and glitch, with the play icon moving up but also flashing in various other places.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=943206#c12

Comment 1

[Kartikaya Gupta (email:[e-mail])]

Attachment: Test case

Comment 2

[Kartikaya Gupta (email:[e-mail])]

Attachment: Test case

Urgh, mixed-content blocking.

Comment 3

[Kartikaya Gupta (email:[e-mail])]

The iframe has height="510" but layout is also reporting that the iframe has scrollTopMax 510, so Fennec allows panning it. Not sure why scrollTopMax is coming back as 510.

Comment 4

[Kartikaya Gupta (email:[e-mail])]

ScrollFrameHelper::GetScrolledRect() is returning the extra-tall rect. That in turn seems to be getting it from mScrolledFrame->GetScrollableOverflowRect().

Comment 5

[Kartikaya Gupta (email:[e-mail])]

Also note that this is reproducible even if you get the click-to-play block on the iframe; just pan the click-to-play gray background and it will scroll.

Comment 6

[Kartikaya Gupta (email:[e-mail])]

So it seems that even on Mac desktop, the iframe's body has a scrollTopMax equal to the height of the iframe. The difference is that the desktop browser respects the overflow:hidden that is also on the body, and so doesn't provide any mechanism for the user to scroll the frame. On Fennec we don't respect the overflow:hidden (there are existing bugs on file for this) and so we allow scrolling.

However I think this is still an underlying layout bug that just so happens to be more easily exposed on Fennec. You can see it on Mac desktop using the scratchpad in the browser chrome environment and inspecting the properties of the iframe.

Also interesting is that although the scrollTopMax of the iframe body is nonzero, the scrollLeftMax is not.

Comment 7

[Kartikaya Gupta (email:[e-mail])]

.. and it turns out that the embedded iframe actually has a second div that is abs-positioned out of sight but with a height that matches the height of the iframe. So layout is probably doing the right thing here, but we just need to support overflow:hidden better on subframes in Fennec.

Sorry for the bugspam/churn in Layout.

Comment 8

[Kartikaya Gupta (email:[e-mail])]

Just to bring this back full circle, I'm going to dupe it to the original bug that dholbert filed on Fennec for embedded youtube things being pannable, since this is not really a general problem with iframes and seems to be pretty limited in scope to iframes that are overflow:hidden.