[Okular-devel] [Bug 272176] New: Document viewport height changes can cause disproportionally large jumps in scroll position

[Eike Hein]

https://bugs.kde.org/show_bug.cgi?id=272176

           Summary: Document viewport height changes can cause
                    disproportionally large jumps in scroll position
           Product: okular
           Version: 0.12.2
          Platform: Fedora RPMs
        OS/Version: Linux
            Status: NEW
          Severity: minor
          Priority: NOR
         Component: general
        AssignedTo: okular-devel at kde.org
        ReportedBy: hein at kde.org


Under certain circumstances, changing the height of the document viewport can
cause the scroll position to change by a significant amount, e.g. about half a
page or so, for no intuitive reason.

Example steps to reproduce:
1. Load a large PDF document with a TOC.
2. Use the TOC sidebar to jump to a specific page.
3. Press Ctrl+M to toggle the menu bar. The scroll position will jump by about
half a page, a much larger amount than the height of the menu bar.

As an alternative to toggling the menu bar, toggling the sidebar pane works too
(probably because it usually causes a horizontal scrollbar to be toggled as
well, causing another viewport height change). This is actually the more common
and annoying scenario for me: I frequently have Okular and a Konsole window
open side-by-side on a small screen because I'm reading a programming-related
text and what to try out in Konsole what I read about. Because my laptop screen
is rather small, I usually collapse the sidebar to maximize the available space
for the document. But occassionally I have to uncollapse it to check something
in the TOC or so - and then the scroll position jumps.

Interestingly step 2 seems to be a necessary condition to reproduce the
problem, although there might be other ways to set this up (it happens
frequently enough for me that there are propably more triggers, but this is the
reliable one I know of). If the document was manually dragged to a position
using the Browse tool the jump doesn't occur (the scroll position will still
change, but only to account for the (dis)appearing menu bar or horizontal
scroll bar).

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