https://bugs.documentfoundation.org/show_bug.cgi?id=156125
Bug ID: 156125
Summary: Slow scrolling of documents with many Math formulas
Product: LibreOffice
Version: 7.5.3.2 release
Hardware: All
OS: Linux (All)
Status: UNCONFIRMED
Severity: normal
Priority: medium
Component: Writer
Assignee: libreoffice-bugs@lists.freedesktop.org
Reporter: jrheinlaen...@users.sourceforge.net
Created attachment 188162
--> https://bugs.documentfoundation.org/attachment.cgi?id=188162&action=edit
Writer file containing numerous Math objects with varying font sizes
When editing a Writer document that has many Math formulas, scrolling can
become irregular.
After examining this with callgrind, I found the reason in
vcl/unx/generic/fontmanager/fontconfig.cxx class CachedFontConfigFontOptions.
Here the font options cache is coded to a size of 10.
Apparently Math formulas can contain a lot of fonts in varying sizes. Thus the
font cache is quickly filled. On scrolling, an enormous amount of calls to
PrintFontManager::getFontOptions() is generated. Unless cached, these are
handled by libfontconfig's FcFontSetMatch(). On typical Ubuntu systems,
several thousand fonts can be installed (run fc-list). Thus libfontconfig uses
a significant time to handle the calls.
Scrolling performance can be greatly improved by increasing the font options
cache size to e.g. 100. Since memory usage is probably not as critical as it
used to be when the font options cache was first implemented, that should be a
safe change.
Find attached a sample file with a lot of Math formulas containing different
font sizes.
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