1063158 - Empty ContainerLayer showing up on most B2G content

Status: RESOLVED WONTFIX

(Core :: Layout, defect)

Description

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

Attachment: Sample layer dump (see scrollId=4)

If you build with bug 1053992 on a Hamachi and enable the FPS display, you'll see the red visual indicator show up in lots of places. For example, while scrolling the homescreen. Or in the settings app. It appears that layout is generating a container layer with no children but with a scrollable metrics, and we are creating an APZC for it. Not sure why yet.

Comment 1

[Timothy Nikkel (:tnikkel)]

I think it's a scroll info layer. They will always get created now because they don't see the creation of a scroll layer item (which is what prompts them to destroy themselves before layer creation time).

Comment 2

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

Is that easy to fix?

Comment 3

[Botond Ballo [:botond]]

I see this on Flame as well.

Comment 4

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: fix!

This should fix it.

Comment 5

[Botond Ballo [:botond]]

Comment on attachment 8485202 [details] [diff] [review]
fix!

Review of attachment 8485202 [details] [diff] [review]:
-----------------------------------------------------------------

Yup, I see no spurious scrollinfo layers with this patch. Thanks!

Comment 6

[Botond Ballo [:botond]]

https://tbpl.mozilla.org/?tree=Try&rev=c452377ac6c8

Comment 7

[Botond Ballo [:botond]]

(In reply to Botond Ballo [:botond] from comment #6)
> https://tbpl.mozilla.org/?tree=Try&rev=c452377ac6c8

I included this patch in my Try push by accident, and since it was the one on top, 'bzpush' marked this bug. I don't suppose it hurts, though.

Comment 8

[Timothy Nikkel (:tnikkel)]

Comment on attachment 8485202 [details] [diff] [review]
fix!

Looks good.

This brings up the question of what to do when there are no scrollable display items in a scroll frame with a display port. Presumably we still want to record a frame metrics somewhere in the layer tree for the APZC to receive. Perhaps in a scroll info layer?

Comment 9

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Yes, I suppose we should do that.

Comment 10

[No-Jun Park [:njpark]]

[Blocking Requested - why for this release]:
Nominating because this fix is required to use Bug 1053992.  Bug 1053992 is needed to test the 2.1 feature bug 1026271.  Kats, could you let me know if I'm mistaken?  Thanks!

Comment 11

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

Yup, that's correct.

Comment 12

[Botond Ballo [:botond]]

Comment on attachment 8485202 [details] [diff] [review]
fix!

Fixed the patch title, now that we know it is indeed a fix :)

Comment 13

[Robert O'Callahan (:roc) (email my personal email if necessary)]

(In reply to Timothy Nikkel (:tn) from comment #8)
> This brings up the question of what to do when there are no scrollable
> display items in a scroll frame with a display port. Presumably we still
> want to record a frame metrics somewhere in the layer tree for the APZC to
> receive. Perhaps in a scroll info layer?

It turns out to be very difficult to have scrollframes create an nsDisplayScrollInfoLayer only when there is no layer with a FrameMetrics for that scrollframe.

So for now I think we should continue with the current setup where every actively scrollable or event-targetable inactive scrollframe generates an nsDisplayScrollInfoLayer which generates a scrollinfo layer. I.e., we should mark this patch WONTFIX.

In bug 1053992 I think we should just suppress the visual marker if there are layers with content and FrameMetrics with the same ID as the FrameMetrics of the scrollinfo layer.

In bug 980544 I will explain how to get rid of scrollinfo layers in the slightly longer term.

Comment 14

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

I filed bug 1064840 for the changes needed to the visual indicator.

Comment 15

[Gordon Brander :gordonb]

Note that we're getting heavy scroll jank as well as visual issues where the scrollbar flickers in and out. Folks from GFX thought these new artifacts were caused by this bug. How do we plan to fix these issues?

Comment 16

[Botond Ballo [:botond]]

(In reply to Gordon Brander :gordonb from comment #15)
> Note that we're getting heavy scroll jank as well as visual issues where the
> scrollbar flickers in and out. Folks from GFX thought these new artifacts
> were caused by this bug. How do we plan to fix these issues?

Scrollbar issues should be fixed by bug 1061327.

If you're seeing scroll jank unrelated to scrollbars, please file a bug with STR and we will investigate.