Bug 414228 - 100% CPU usage and lag when scrolling
Summary: 100% CPU usage and lag when scrolling
Status: REPORTED
Alias: None
Product: okular
Classification: Applications
Component: general (show other bugs)
Version: 1.8.3
Platform: Arch Linux Linux
: NOR normal
Target Milestone: ---
Assignee: Okular developers
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2019-11-17 12:26 UTC by Lars Veldscholte
Modified: 2019-11-17 12:44 UTC (History)
1 user (show)

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Description Lars Veldscholte 2019-11-17 12:26:40 UTC 
SUMMARY
Scrolling of PDF files in Okular 1.8.3 is very laggy and consumes 100% CPU (on one thread) while the scrolling animation is running.

STEPS TO REPRODUCE
1. Open a PDF file in Okular.
2. Scroll.

OBSERVED RESULT
The scrolling animation has low framerate, lags behind the input actions, and consumes 100% CPU on one thread.

EXPECTED RESULT
Smooth, snappy scrolling.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma
KDE Plasma Version: 5.17.3
KDE Frameworks Version: 5.64.0
Qt Version: 5.13.2

ADDITIONAL INFORMATION
Comment 1 Yuri Chornoivan 2019-11-17 12:36:44 UTC 
Does it happen for every possible file or just for the files with images/background? If it is some specific file can you share it for testing?

Does switching off optimizations in "Settings -> Configure Backends..." help?

Are you running the default Okular without any additional configurations?

Thanks in advance for your answers.
Comment 2 Lars Veldscholte 2019-11-17 12:39:33 UTC 
It happens with every PDF I've tried so far. In fact, it even happens with plain text files; it seems to be unrelated to the backend.

This is just Okular from the Arch repositories, I did not customise it in any way.
Comment 3 Yuri Chornoivan 2019-11-17 12:44:32 UTC 
The answers were given.