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Bug 133849 - Automatic spell check in calc with many misspelled words causes high CPU load scrolling and text movement
Summary: Automatic spell check in calc with many misspelled words causes high CPU load...
Alias: None
Product: LibreOffice
Classification: Unclassified
Component: Calc (show other bugs)
(earliest affected) release
Hardware: All All
: medium normal
Assignee: Not Assigned
Whiteboard: QA:needsComment
Depends on:
Blocks: Spell-Checking
  Show dependency treegraph
Reported: 2020-06-10 09:02 UTC by Telesto
Modified: 2020-09-15 17:29 UTC (History)
2 users (show)

See Also:
Crash report or crash signature:


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Description Telesto 2020-06-10 09:02:25 UTC
The spell checker in Calc only checks the on screen part of wrong spelled words. In principle no issue with that. However if you start scrolling, the spell checker 'restarts' checking everything on screen. So also the already checked part. Nothing is cached..

So spell checker is doing same stuff multiple times.. At the same time causes the restart the spell checker repaints of the red underlining.. which means shaping text over and over. And shaping text isn't cheap anymore (since Harfbuzz). 

Which - both together - creates an massive CPU load while scrolling moving text 

Steps to Reproduce:
1. Open the attached file
2. Automatic spell check enabled. Scroll up down & monitor CPU usage

Actual Results:
15-25% depending on scroll speed etc

Expected Results:
Can be improved

Reproducible: Always

User Profile Reset: No

Additional Info:
Version: (x64)
Build ID: 59939d2490726336546c7ad05082d23031074e12
CPU threads: 4; OS: Windows 6.3 Build 9600; UI render: default; VCL: win
Locale: nl-NL (nl_NL); UI: en-US
Calc: CL