Memory leak (OpenCV + QML)

DYYF

Hi! I’m trying to display OpenCV Mat in QML image.

I grab frames from camera with OpenCV, the frames are displayed successfully in QML, but memory usage increases with time. How can I fix it? Here is the my code:

main.cpp

#include <QGuiApplication>
#include "videoprovider.h"

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

    VideoProvider videoProvider;

    return app.exec();
}

VideoProvider.h

#ifndef VIDEOPROVIDER_H
#define VIDEOPROVIDER_H

#include <QObject>
#include <QFuture>
#include <QImage>
#include <QQmlApplicationEngine>
#include <QQuickImageProvider>
#include <opencv2/opencv.hpp>

class VideoProvider : public QObject, public QQuickImageProvider
{
    Q_OBJECT
public:
    explicit VideoProvider();
    QPixmap requestPixmap(const QString &id, QSize *size, const QSize& requestedSize);

signals:
    void frameChanged();

public slots:
    void framePainted();

private:
    QQmlApplicationEngine engine;
    bool readyfor;
    cv::Mat mat;
    QImage outputImage;
    void process();
};

#endif // VIDEOPROVIDER_H

VideoProvider.cpp

#include <QQmlContext>
#include <QtConcurrent/QtConcurrent>
#include <QDebug>
#include <QThread>
#include "videoprovider.h"
#include <QQuickImageProvider>

VideoProvider::VideoProvider() : QQuickImageProvider (QQuickImageProvider :: Pixmap)
{
    engine.rootContext()->setContextProperty("videoProvider", this);

    engine.addImageProvider(QLatin1String ("videoCapture"), this);

    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

    readyfor = true;

    QtConcurrent::run(this, VideoProvider::process);
}

void VideoProvider::framePainted()
{
    readyfor = true;
}

void VideoProvider::process()
{
    cv::VideoCapture capture(0);

    while(true){

        QThread::currentThread()->msleep(80);

        if(!readyfor) continue;

        mat.release();

        capture >> mat;

        if(mat.empty())
        {
            qDebug()<<"disconnect";
        }
        else
        {
            readyfor = false;

            cv::cvtColor(mat, mat, cv::COLOR_BGR2RGB);

            outputImage = QImage((uchar*)mat.data, mat.cols, mat.rows, mat.step, QImage::Format_RGB888);

            emit frameChanged();
        }
    }

    capture.release();
}

QPixmap VideoProvider::requestPixmap(const QString &id, QSize *size, const QSize& requestedSize)
{
    return QPixmap::fromImage(outputImage);
}

main.qml

import QtQuick 2.6
import QtQuick.Window 2.2

Window
{
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")
    id: root

    Image {
        id: videoLayer
        anchors.fill: parent
        cache: false

        onSourceChanged:{
            videoProvider.framePainted();
        }
    }
 
    Connections
    {
        target: videoProvider
        property int frameCounter: 0

        onFrameChanged:
        {
            videoLayer.source = "image://videoCapture/hoge" + frameCounter;
            frameCounter ^= 1;
        }
    }
}

I found that it happened when I send signal (emit frameChanged();) to QML.

Pablo J. Rogina

@DYYF have you tried any other examples for OpenCV + QML? i.e. here or here?
I'm not sure why, but I don't like your videoprocessor object launching the QML engine. All the examples I've used to so far run the QML engine from main.cpp