[Tokodon] [Bug 501936] New: Page Up / Page Down can cause posts to disappear

[bugzilla_noreply at kde.org]

https://bugs.kde.org/show_bug.cgi?id=501936

            Bug ID: 501936
           Summary: Page Up / Page Down can cause posts to disappear
    Classification: Applications
           Product: Tokodon
           Version: 24.12.2
          Platform: Arch Linux
                OS: Linux
            Status: REPORTED
          Severity: minor
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: huguesross at posteo.com
                CC: carl at carlschwan.eu, josh at redstrate.com
  Target Milestone: ---

Created attachment 179688
  --> https://bugs.kde.org/attachment.cgi?id=179688&action=edit
Pair of screenshots showing the timeline before & after reproducing this bug

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SUMMARY


STEPS TO REPRODUCE
1. Open your timeline. You must be able to see two or more posts to reproduce
the issue
2. Scroll down as little as possible, just enough for scrolling up to be
possible
3. Press Page Up (This bug can also be reproduced at the bottom of a thread
using Page Down)

OBSERVED RESULT
The bottom-most post disappears (that is to say, it becomes an empty space)
until you scroll again, at which point it re-appears.

EXPECTED RESULT
The bottom-most post remains visible, as it is still in the viewport.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
This is a 100% repro on my system, I can easily do it on command if more info
is needed

I know nothing about the structure of this software, but as a software
developer I have a suspicion about its origins:
- When Page Up is pressed, the offset of the viewport is clamped by the upper
bounds of the page
- ...but the process that determines which widgets to render / cull receives
the original un-clamped value
- As such, the bottom-most post appears to be "off the page" to this algorithm
and is no longer rendered until the viewport scrolls again

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