[okular] [Bug 409644] New: [Wayland] Panning is laggy

[Simone]

https://bugs.kde.org/show_bug.cgi?id=409644

            Bug ID: 409644
           Summary: [Wayland] Panning is laggy
           Product: okular
           Version: unspecified
          Platform: Archlinux Packages
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: PDF backend
          Assignee: okular-devel at kde.org
          Reporter: s.scalabrino9 at gmail.com
  Target Milestone: ---

Okular version: 19.04.2

SUMMARY
Using a 4K external display with my laptop in Wayland makes the "Browse tool"
very laggy. For example, if I press the left mouse button, I move the pointer
and I release the button, the viewing area of the PDF moves, but 4/5 times more
slowly than the mouse pointer, i.e., it keeps moving when I release the button.
If I do the same in the "Thumbnails" area, instead, it works correctly.
I think this is similar to https://bugs.kde.org/show_bug.cgi?id=387567.

I can experience the problem when: 
1) the "Browse tool" is used in the PDF area;
2) the scrollbar of the PDF area is moved. 

Okular works correctly when:
1) I browse the thumbnails of the PDF;
2) I use the mouse wheel.


STEPS TO REPRODUCE
1. Open a PDF Okular with a 4K external monitor connected
2. Press the left button in the PDF view area, move the pointer, release the
button

OBSERVED RESULT
The movement is significantly slower than the pointer, the viewport keeps
moving even after the mouse button is released.

EXPECTED RESULT
The viewport moves as fast as the mouse pointer and it stops when the left
button is released.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 5.1.15-arch1
(available in About System)
KDE Plasma Version: 5.16.2
KDE Frameworks Version: 5.59.0
Qt Version: 5.13.0
Monitors: dual monitor, one 4K (external, scaled 2x), one 1080p (integrated in
the laptop, not scaled)
VGA controller: Intel Corporation UHD Graphics 630

ADDITIONAL INFORMATION
This happens only in Wayland, not in X11. If I remember correctly, it doesn't
happen when I don't connect the external monitor.

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