[okular] [Bug 420492] New: 20.04.0 significantly slows down mouse scrolling

[roger truong]

https://bugs.kde.org/show_bug.cgi?id=420492

            Bug ID: 420492
           Summary: 20.04.0 significantly slows down mouse scrolling
           Product: okular
           Version: 20.04.0
          Platform: Archlinux Packages
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: okular-devel at kde.org
          Reporter: dragonrmartin at gmail.com
  Target Milestone: ---

SUMMARY
20.04.0 update breaks fast scrolling in Okular. Most noticeable with a
"hyperscroll" mouse wheel.

STEPS TO REPRODUCE
1. open any PDF or EPub file in 20.04.0
2a. with a hyperscroll mouse, free scroll the mouse wheel inside the document
panel
2b. with a normal mouse, scroll as fast as possible inside the document window
3. downgrade to 1.9.3 and repeat step 2

OBSERVED RESULT
Scrolling the same amount of clicks scrolls down less lines in 20.04.0 compared
to 1.9.3. Scrolling with a hyperscroll wheel significantly limits the speed of
scrolling to make free scrolling unusable. This bug is only observed when
scrolling in the document panel. Scrolling in the navigation panel or in the
scrollbar on the right produces the expected scroll speed.

EXPECTED RESULT
The scroll speed in the document panel is as fast as in the other panels and
keeps the same speed as 1.9.3

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 5.18.4.1-1
KDE Frameworks Version: 5.69.0
Qt Version: 5.14.2 (built against 5.14.2)

ADDITIONAL INFORMATION
Mouse: Logitech G502 with free scroll
also tested with a generic mouse with normal scroll wheel

videos of the scrolling attached:
https://youtu.be/wIts9r-meME
https://youtu.be/nfDjuFkjQLE

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