Connecting QQuickImageProvider



  • Hello all!

    I have to connect a QQuickImageProvider with a class to pass an image that the image provider must return, but I am not finding a way to do that. Could someone help me?

    Code below

    main.cpp

    #include <QGuiApplication>
    #include <QQmlApplicationEngine>
    
    #include <QtQml>
    
    #include "processaimagem.h"
    #include "provedorimagem.h"
    
    int main(int argc, char *argv[])
    {
        QGuiApplication app(argc, argv);
    
        qmlRegisterType<processaImagem>("ProcessaImagemQml", 1, 0, "ProcessaImagem");
    
        QQmlApplicationEngine engine;
    
        provedorImagem *provedorImg = new provedorImagem;
    
        //------------  I have to create a connection here between the provider slot and a signal in processaImagem with the image to provide  -----------------
    
        engine.addImageProvider("provedor", provedorImg);
    
        engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
    
        return app.exec();
    }
    

    processaImagem.h

    #ifndef PROCESSAIMAGEM_H
    #define PROCESSAIMAGEM_H
    
    #include <QObject>
    #include <QImage>
    #include <QQmlEngine>
    #include <QQmlContext>
    #include <QQuickImageProvider>
    
    #include "provedorimagem.h"
    
    class processaImagem : public QObject
    {
        Q_OBJECT
    
    public slots:
        QString recebeImagem(const QString &caminho);
    
    public:
        processaImagem(QObject *parent = 0);
    
        QImage carregaImagem(const QString &caminho);
    
    signals:
        void enviaImagem(QImage);
    };
    
    #endif // PROCESSAIMAGEM_H
    

    processaImagem.cpp

    #include "processaimagem.h"
    
    #include <QDebug>
    
    processaImagem::processaImagem(QObject *parent)
    {
    
    }
    
    QString processaImagem::recebeImagem(const QString &caminho)
    {
        QImage imagem = this->carregaImagem(caminho);
    
        QString caminhoRetorno;
    
        if(imagem.isNull())
        {
            qDebug() << "Erro ao receber a imagem";
        }
        else
        {
            qDebug() << "Imagem recebida";
            caminhoRetorno = "image://provedor/imagemEditada";
        }
    
        return caminhoRetorno;
    }
    
    QImage processaImagem::carregaImagem(const QString &caminho)
    {
        QUrl caminhoImagem(caminho);
        QQmlEngine *engine = QQmlEngine::contextForObject(this)->engine();
        QQmlImageProviderBase *imageProviderBase = engine->imageProvider(caminhoImagem.host());
        QQuickImageProvider *imageProvider = static_cast<QQuickImageProvider*>(imageProviderBase);
    
        QSize imageSize;
        QString imageId = caminhoImagem.path().remove(0, 1);
        QImage imagem = imageProvider->requestImage(imageId, &imageSize, imageSize);
    
        if(imagem.isNull())
        {
            qDebug() << "Erro ao carregar a imagem";
            imagem = QImage();
        }
        else
        {
            qDebug() << "Imagem carregada";
        }
    
        return imagem;
    }
    

    provedorimagem.h

    #ifndef PROVEDORIMAGEM_H
    #define PROVEDORIMAGEM_H
    
    #include <QImage>
    #include <QQuickImageProvider>
    
    class provedorImagem : public QQuickImageProvider
    {
    public:
        provedorImagem();
    
        QImage requestImage(const QString &id, QSize *size, const QSize &requestedSize);
    
        void carregaImagem();
    
    public slots:
        void carregaImagem(QImage imagemRecebida);
    
    private:
        QImage imagem;
    };
    
    #endif // PROVEDORIMAGEM_H
    

    provedorimagem.cpp

    #include "provedorimagem.h"
    
    #include <QDebug>
    
    provedorImagem::provedorImagem() : QQuickImageProvider(QQuickImageProvider::Image)
    {
    
    }
    
    QImage provedorImagem::requestImage(const QString &id, QSize *size, const QSize &requestedSize)
    {
        if(imagem.isNull())
        {
            qDebug() << "Erro ao prover a imagem";
        }
        else
        {
            qDebug() << "Imagem provida";
        }
    
        return imagem;
    }
    
    void provedorImagem::carregaImagem(QImage imagemRecebida)
    {
        imagem = imagemRecebida;
    }
    

  • Lifetime Qt Champion

    Hi,

    Why not just emit a signal from the provider and connect it to whatever class you need ?



  • @SGaist Hello. Thanks for the reply.

    Because what I need is a slot in the provider to receive an QImage and return it from the provider to QML.


  • Lifetime Qt Champion

    Can you describe your use case ?



  • Answering my own question
    Problem solved. Here is the solution step by step:

    1 - Create a class that inherits from QQuickImageProvider and QObject and inside it create a Image member (QImage) that is the image to be provided.

    class provedorImagem : public QObject, public QQuickImageProvider
    

    Implement the virtual requestImage method. This is the method that will return the image to Qml

    QImage requestImage(const QString &id, QSize *size, const QSize &requestedSize)
    

    Create a method to load the provider’s image to return

    void provedorImagem::carregaImagem(QImage imagemRecebida)
    {
        imagem = imagemRecebida;
    }
    

    Now set it as the engine image provider in the main.cpp file

    provedorImagem *provedorImg = new provedorImagem;
    engine.rootContext()->setContextProperty("ProvedorImagem", provedorImg);
    

    2 - Create another class that inherits from QObject.

    class processaImagem : public QObject
    

    Inside this class you must implement a method that will get the image from camera provider, perform the image modifications and return the modified image.
    PS: The p_caminhoImagem is a property that I created inside the processaImagem class that receives the camera preview path.

    QImage processaImagem::carregaImagem()
    {
        QUrl caminhoImagem(p_caminhoImagem);
        QQmlEngine *engine = QQmlEngine::contextForObject(this)->engine();
        QQmlImageProviderBase *imageProviderBase = engine->imageProvider(caminhoImagem.host());
        QQuickImageProvider *imageProvider = static_cast<QQuickImageProvider*>(imageProviderBase);
    
    
        QSize imageSize;
        QString imageId = caminhoImagem.path().remove(0, 1);
        QImage imagem = imageProvider->requestImage(imageId, &imageSize, imageSize);
    
        if(imagem.isNull())
        {
            imagem = QImage();
        }
        else
        {
            //Perform the modifications
        }
    
        return imagem;
    }
    

    3 - Now is the main part. The image requestImage provider method must receive the modified image from the processaImagem class to provide it to QML. To do it the provider class pointer must be accessible to the QML file, so, in the main.cpp file just make the pointer available to QML as a property

    engine.rootContext()->setContextProperty("ProvedorImagem", provedorImg);
    

    and register the processaImagem class as a QML type

    qmlRegisterType<processaImagem>("ProcessaImagemQml", 1, 0, "ProcessaImagem");
    

    Now we link it inside the QML file

    ProvedorImagem.carregaImagem(processaImagem.carregaImagem());
    

    4 - It is done. Now just request the image from the provider:

    imagemPreview.source = "image://provedor/imagemEditada_" + camera.numeroImagem.toString();

  • Lifetime Qt Champion

    But why not do the processing directly in the image provider ?



  • Can be done directly in the image provider, but it still needs to have a class to send the image to the image provider.


  • Lifetime Qt Champion

    Why not grab the image in the image provider ?



  • @SGaist How?


  • Lifetime Qt Champion

    Unless I'm mistaken all what your processaImagem does is get the image from the image provider, apply some modification and set it again on the image provider, right ?



  • Yes, but are the camera image provider and my own image provider the same?


  • Lifetime Qt Champion

    Are you using the Camera QML type to grab the image from the camera ?



  • Yes, and after that I am performing some modifications and return a square image.


  • Lifetime Qt Champion

    In that case, why not use a ShaderEffect to "cut" your image square ?



  • @SGaist
    Because I didnt know that ShaderEffect can "cut" an image. I read the documentation and I could not find how to do it with ShaderEffect.

    Now I am interested about how to perform the image modifications directly in the provider. How can I pass the image without other class to do it?

    Another thing, the modifications performed in the image include rotate the image in case of wrong image orientation.


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