kcalc > KCalcButton::paintEvent mallocs more than 80 MB per minute

[Marius P]

Hello,

Would an improvement for the issue below. Constitute material for the KDE
Eco initiative?
If so, I am a senior C++ developer. I do not know Qt. I have more than 2
hours per week to dedicate to the issue below. I will need help.

The ideal situation would be to not do custom painting.

Technical details:

As per
https://blogs.gnome.org/chergert/2020/03/15/how-to-use-sysprof-to-part-ii/
chapter "Reducing Memory Allocations". kcalc in
https://invent.kde.org/utilities/kcalc/-/blob/master/kcalc_button.cpp#L133
for each button, does custom painting. mallocs e.g. in QTextDocument ctor
and in QTextDocument::setHtml(). The button's custom painting method uses
HTML mainly for center aligning/justifying text.

    ALLOCATED      TOTAL    FUNCTION
[   81.1 MiB] [  69.04%]
 KCalcButton::paintEvent(QPaintEvent*)
[   23.7 MiB] [  20.20%]
 QTextDocument::QTextDocument(QObject*)
[   15.7 MiB] [  13.35%]
 QTextDocument::setHtml(QString const&)
[   12.0 MiB] [  10.21%]
 QTextDocument::size() const
[   10.3 MiB] [   8.74%]                                        In file
/usr/lib/x86_64-linux-gnu/qt5/plugins/styles/breeze.so
[    6.6 MiB] [   5.59%]
 QTextDocumentLayout::draw(QPainter*,
QAbstractTextDocumentLayout::PaintContext const&)

Thanks.
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