Render/Layout performance very slow. High CPU usage for only 20 QLabels in 30fps

[marcj]

I tried now as you guys suggested the QT Quick Widgets, which should be rendered with OpenGL and with performance in mind (I mean it should run on mobile devices right?). Result is not really satisfying, I guess even worse. 100 labels, 30fps -> 33% CPU burn.

Code for that:

//main.cpp
#include <QGuiApplication>
#include <QTimer>
#include <QQuickItem>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("main.qml")));

    QQuickItem *list = engine.rootObjects()[0]->findChild<QQuickItem *>(QString("list"),
                                                                         Qt::FindChildrenRecursively);

    QTimer *timer = new QTimer();
    timer->setInterval(1000/30);
    int counter = 0;

    QObject::connect(timer, &QTimer::timeout, [&] {
        counter++;
        for(auto const& item: list->childItems()) {
            item->setProperty("text", QString("WTF %1").arg(counter));
        }
    });

    timer->start();

    return app.exec();
}

import QtQuick 2.6
import QtQuick.Controls 2.0

ApplicationWindow {
    id: root
    width: 600
    height: 500
    visible: true

    Grid {
        objectName: "list"
        rows: 50
        columns: 10
        spacing: 10

        Repeater {
            model: 100;
            objectName: "repeater"
            Label {
                text: "Hello world"
                width: 60
                objectName: "label" + index
            }
        }
    }
}

[SGaist]

If you'd like to go on with raw OpenGL, then the Qt OpenGL and GUI modules are what you want to look at, they provide everything you need to write OpenGL application.