[Libreoffice-bugs] [Bug 133849] New: Automatic spell check in calc with many misspelled words causes high CPU load scrolling and text movement

[bugzilla-daemon at bugs.documentfoundation.org]

https://bugs.documentfoundation.org/show_bug.cgi?id=133849

            Bug ID: 133849
           Summary: Automatic spell check in calc with many misspelled
                    words causes high CPU load scrolling and text movement
           Product: LibreOffice
           Version: 5.3.0.3 release
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: medium
         Component: Calc
          Assignee: libreoffice-bugs at lists.freedesktop.org
          Reporter: telesto at surfxs.nl

Description:
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: 7.1.0.0.alpha0+ (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

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