It is safe to call QCustomPlot::replot() with QCustomPlot::rpRefreshHint in another thread? I know that is not a good idea to manipulate QWidget from other threads, But my problem was plotting 6k(1k per graph) points in 5 instance of QCustomPlot(points are added using QCPGraph::addData() and I got performance issues with QCustomPlot::replot().
So I tried to move QCustomPlot::replot to another thread and it just work fine without any issue and the performance problem was fixed.
Sample Code:
#include "qcustomplot.h"
#include <QApplication>
#include <QPointer>
#include <QVector>
#include <QThread>
#include <QTimer>
#include <QTime>
class QCustomPlotUpdater : public QObject {
public:
QCustomPlotUpdater(QVector<QPointer<QCustomPlot>> const& plots)
: plots_(plots),
thread_(new QThread),
start_time_(QTime::currentTime()) {
connect(thread_, &QThread::finished, this, &QObject::deleteLater);
connect(thread_, &QThread::started, &updater_, qOverload<>(&QTimer::start));
connect(&updater_, &QTimer::timeout, this, &QCustomPlotUpdater::addNewPoint);
updater_.setInterval(std::chrono::milliseconds(16));
}
void start() {
thread_->start();
}
private:
void addNewPoint() {
double const key = start_time_.msecsTo(QTime::currentTime()) / 1000.0;
for (auto const& plot : plots_) {
for (int index = 0, end = plot->graphCount(); index < end; ++index) {
plot->graph(index)->addData(
key * ((index + 1) * 0.25),
qSin(key) + std::rand() / (double)RAND_MAX * 1 * qSin(key / 0.3843));
}
plot->rescaleAxes();
plot->replot(QCustomPlot::rpRefreshHint);
}
}
QVector<QPointer<QCustomPlot>> plots_;
QPointer<QThread> thread_;
QTime const start_time_;
QTimer updater_;
};
auto CreateCustomPlot() {
QPointer<QCustomPlot> result = new QCustomPlot;
for (int i = 0; i < 4; ++i) result->addGraph();
result->setMinimumSize(500, 300);
return result;
}
int main(int argc, char* argv[]) {
QApplication app(argc, argv);
QVector plots = {
CreateCustomPlot(),
CreateCustomPlot(),
CreateCustomPlot(),
CreateCustomPlot(),
};
auto* const updater = new QCustomPlotUpdater(plots);
updater->start();
for (auto const& plot : plots) plot->show();
app.exec();
}
You could find the complete project files here: https://gist.github.com/another-ghasem/5052517283d14968339c4177b86181f0
I also tried compiling with: -fsanitize=undefined,thread and it's report nothing.
- Compiler: Debian clang version 11.0.1-2~deb10u1
- OS: Debian Buster 4.19.235-1
- Qt: 5.15.2
- QCustomPlot: 2.1.0, released on March 29, 2021