[pdf] Changing the orientation while using the lateral scroll bar make the bar crazy

[Emanuele Sorce]

If you are, using the lateral bar, browsing the pdf file and you change orientation keeping moving the bar.
Expected: The bar should simply go when the finger is when the changing of orientation finishes; and all should be ok.
The bug is: After you do that, if you try to touch the bar or move it, the bar will become crazy and continue moving up and down, making hard or not nice to get where you want.

[Stefano Verzegnassi (verzegnassi-stefano)]

While I find very hard to think at a valid user scenario which could trigger this issue pretty often (and this could lead to a low importance), the bug currently exists.

Document Viewer just uses standard Ubuntu Components and can not edit the rotation behaviour in any way, therefore the bug needs to be fixed elsewhere.

I'm adding 'canonical-devices-system-image' as affected project, and contextually marking the report as Incomplete for 'ubuntu-docviewer-app', in wait for further informations from the Canonical engineers/managers.

Anyway, I checked on my Android phone and it seems that the OS always delays the screen rotation as long as there's an on-going touch event (e.g. 'onPressed' event).

This is something it would be necessary to implement in Ubuntu too (in the Ubuntu UI Toolkit, or whatever manages screen rotation - i.e. Mir or the Unity8 shell).

[Stefano Verzegnassi (verzegnassi-stefano)]

Talking about the bug itself, I didn't found any crazy behaviour from Document Viewer while I was trying to reproduce this issue. It's reasonable for me that the cursor is moved at the top of the view since it's where my finger is.

Indeed, the scroll bar kept working properly, taking account of the position of my finger.

In any case, it would be worth to fix the other issue I mentioned above, and that would also fix any ambiguous behaviour, like the one you reported.

Thanks for taking some time for improving the Ubuntu platform! :)

[Andrea Bernabei (faenil)]

I can reproduce the bug by just zooming in a pdf and dragging the vertical scrollbar, no orientation change required. The bug does not show with the horizontal scrollbar.

Stefano can you please make sure this behaviour is not a consequence of using the custom flickable-like component that the PDF view is using?

Once you're sure the bug is in the Scrollbar, please affect "ubuntu-ui-toolkit (Ubuntu)" and assign it to me ;)

[Stefano Verzegnassi (verzegnassi-stefano)]

I'm really sorry with you, Emanuele, for misunderstanding what you meant.

@Andrea: I'm able to reproduce the issue now, and I can explain which is the reason of the bug.

The ListView we use does not return properly the size of the content, but it just estimates where content should be with some approximation. So yes, you're right.

- Just a bit of historical context:

The current PDF viewer is still using the code I added in February 2015, in order to have a first implementation of the zoom gesture in time for the release of the BQ E4.5.

I decided to use that component, which comes from Unity 8, with the idea to rewrite the whole plugin once I had more time. It seemed a good compromise at the time, since they told me that the BQ phone would have been released in a few weeks, and there was probably no enough time to test a new backend.

Actually it wasn't that good idea, since Canonical asked us to focus on the LibreOffice viewer instead, and we're still using that PDF viewer prototype.

The Document Viewer currently has no maintainer, like many other Core Apps. I'm discussing with Alan how we could maintain the application, since I stopped my contributions to the Core Apps but I have anyway a new PDF backend I wrote in my spare time.

[Stefano Verzegnassi (verzegnassi-stefano)]

About the other (UX) issue I mentioned in comment #1, I still think it could be worth to fix it, since I would never expect a screen rotation while there's an on-going touch event.