https://bugs.kde.org/show_bug.cgi?id=420747
Bug ID: 420747
Summary: KQuickAddons.Plotter skips repaints
Product: frameworks-kdeclarative
Version: 5.69.0
Platform: Gentoo Packages
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: notm...@gmail.com
Reporter: konstantinos.sma...@gmail.com
CC: kdelibs-b...@kde.org
Target Milestone: ---
Created attachment 127986
--> https://bugs.kde.org/attachment.cgi?id=127986&action=edit
Screencast (applet update interval: 1 second)
SUMMARY
The KQuickAddons.Plotter used for the System Monitor applets occasionally skips
repaints, leading to jumpy plots.
More specifically, the skips occur because the plot itself will not be
repainted unless another element in the QML scene changes. According to my
understanding, Plotter::addSample() triggers Plotter::update(), which in turn
triggers Plotter::updatePaintNode(). However, Plotter::updatePaintNode() only
seems to be initializing the paint node, not actually rendering it (why?),
therefore relying only on the QQuickWindow::beforeRendering signal to trigger
Plotter::render(). As a result, even if you add new samples to the plot, they
will be rendered only if another element in the QML scene requires to be
repainted.
For example, in the CPU load monitoring applet, if the CPU load remains the
same across multiple measurements, the applet will not be repainted until a
different CPU load measurement comes up. This can be observed in the attached
screencast twice:
* the first time, the CPU load remains at 14% for two ticks, leading to one
missed repaint
* the second time, the CPU load remains at 14% for four ticks, leading to
three missed repaints
STEPS TO REPRODUCE
1. Observe any system monitor applet (preferably in plasmoidviewer or on the
desktop, because on a panel other applets will trigger a repaint)
2. Wait for multiple same measurements
OBSERVED RESULT
The applet is not repainted while the measurement remains the same. It is only
updated when a different measurement comes up.
EXPECTED RESULT
The applet should be repainted for every measurement.
SOFTWARE/OS VERSIONS
Operating System: Gentoo Linux
KDE Plasma Version: 5.18.4
KDE Frameworks Version: 5.69.0
Qt Version: 5.14.1
Kernel Version: 5.6.7-gentoo
OS Type: 64-bit
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