thumbnails missing from Top Sites view

[Bill Filler]

On all of my devices (arale, krillin and N4), the Top Sites page frequently has empty thumbnails for some of it's listings. I have not dug into steps to reproduce, but am experiencing this on all of my devices. This needs to be debugged further and fixed. Let me know what information needs to be provided if you cannot reproduce it.

[Olivier Tilloy (osomon)]

I’m seeing the same problem, will need to dig into it.

[Olivier Tilloy (osomon)]

I’m seeing that too on my devices, and I’ve been able to "fix" it by doing the following:

 1) open a new tab
 2) in the new tab view, switch to the top sites grid if needed, identify one top site that doesn’t have a thumbnail, and tap/click it
 3) open a new tab again, and go back to step #2 until all top sites have thumbnails

As a corollary, a possible explanation for the bug is that missing thumbnails were never generated in the first place.
A thumbnail is generated shortly before a tab becomes invisible, so typically switching between tabs or opening a new tab will generate a thumbnail for the tab that was current. On the other hand, closing the current tab or using the address bar to browse to a different website in an existing tab won’t generate a thumbnail.

My suspicion is that those top sites that are missing a thumbnail are typically being browsed to, and then either the tab is closed or the address bar is used to browse to a different site.

To fix that, we need to find the right moment to generate a thumbnail for the current tab, once it has finished rendering.

[Olivier Tilloy (osomon)]

When closing a tab, its 'current' property becomes false, and as a consequence a capture is requested. However it never manages to complete because in the meantime the tab object has been destroyed. This could be worked around by delaying the destruction until after the capture has been taken, but it wouldn’t solve the case where one re-uses the same webview to navigate to a different site.

[Bill Filler (bfiller)]

We should also make sure of the following:
- display some sort of placeholder graphic (we used to have something iirc) in the case where thumbnail is not generated
- make sure whatever fix we apply to solve this issue is also used when generating previews that appear in tabs, as I've also seen cases (although not as common) where the tab previews are empty and could be the same root cause.

[Olivier Tilloy (osomon)]

The fix in the linked branch should cater for the second issue, because a capture will be taken (almost) as soon as the page is finished loading, and it won’t be deleted until the page is closed.

Regarding the first point, I’ll talk to design about it.

[Launchpad Janitor (janitor)]

This bug was fixed in the package webbrowser-app - 0.23+16.04.20160215.1-0ubuntu1

---------------
webbrowser-app (0.23+16.04.20160215.1-0ubuntu1) xenial; urgency=medium

  [ CI Train Bot ]
  * Resync trunk.

  [ Olivier Tilloy ]
  * Add keyboard navigation support to narrow views (new tab view,
    history view, bookmarks view, downloads view). (LP: #1539221)
  * Add video-specific contextual actions. (LP: #1539676)
  * Take a capture of the current page shortly after it has finished
    loading to give rendering an opportunity to complete. (LP: #1540129)
  * Use the new bottom edge bar to open the tabs view in autopilot
    tests.

 -- Olivier Tilloy <email address hidden> Mon, 15 Feb 2016 13:33:21 +0000