Save QGraphicsScene (with OpenGL items) to JPEG

[MadBear]

Greetings,

I have a strange problem. I have created application where user can create several QGraphicsScenes (shown is only one in main view) and since I had to use OpenGL for some items I have also used OpenGL (FBO) to save current scene as JPEG image. Now it works great until I have several scenes in "script" and some of those scenes use QGraphicsTextItem. In that case text is not rendered correctly (it is rendered only as a filled box). That does not occur if there is only one scene. In that case text is rendered correctly. What am I doing wrong? The relevant code is:

QGLFramebufferObject *mbuff=new QGLFramebufferObject(width(),height());
        QStyleOptionGraphicsItem pom;
        mbuff->bind();
        glPushAttrib(GL_ALL_ATTRIB_BITS);
        glViewport(0,0,mbuff->width(),mbuff->height());
        glMatrixMode(GL_PROJECTION);
        glPushMatrix();
        glLoadIdentity();
        glOrtho(0,mbuff->width(),0,mbuff->height(),-100,100);
        glMatrixMode(GL_MODELVIEW);
        glPushMatrix();
        glLoadIdentity();
        QPainter paint;
        paint.begin(mbuff);
        paint.setRenderHint(QPainter::HighQualityAntialiasing,true);
        QList<QGraphicsItem*> list=items(Qt::AscendingOrder);
        int i;
        for(i=0;i<list.size();i++)
        {
            paint.save();
            paint.setMatrix(list[i]->sceneMatrix(),true);
            list[i]->paint(&paint,&pom,NULL);
            paint.restore();
        }
        glPopMatrix();
        glMatrixMode(GL_PROJECTION);
        glPopMatrix();
        glPopAttrib();
        paint.end();
        mbuff->release();
        QImage pix=mbuff->toImage();
        pix.save(fn);
        delete mbuff;

QGLFramebufferObject *mbuff=new QGLFramebufferObject(width(),height());
        QStyleOptionGraphicsItem pom;
        mbuff->bind();
        glPushAttrib(GL_ALL_ATTRIB_BITS);
        glViewport(0,0,mbuff->width(),mbuff->height());
        glMatrixMode(GL_PROJECTION);
        glPushMatrix();
        glLoadIdentity();
        glOrtho(0,mbuff->width(),0,mbuff->height(),-100,100);
        glMatrixMode(GL_MODELVIEW);
        glPushMatrix();
        glLoadIdentity();
        QPainter paint;
        paint.begin(mbuff);
        paint.setRenderHint(QPainter::HighQualityAntialiasing,true);
        QList<QGraphicsItem*> list=items(Qt::AscendingOrder);
        int i;
        for(i=0;i<list.size();i++)
        {
            paint.save();
            paint.setMatrix(list[i]->sceneMatrix(),true);
            list[i]->paint(&paint,&pom,NULL);
            paint.restore();
        }
        glPopMatrix();
        glMatrixMode(GL_PROJECTION);
        glPopMatrix();
        glPopAttrib();
        paint.end();
        mbuff->release();
        QImage pix=mbuff->toImage();
        pix.save(fn);
        delete mbuff;

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I am realy at a loss here. I have tried software rendering but it is very slow.

Thank you in advance.

Regards,
MadBear

[stampede]

to save current scene as JPEG image

How about using the QGraphicsScene::render method ?

void MyGraphicsScene::renderToFile( const QString& path ){
    QImage img(outputSize,QImage::Format_RGB32);
    QPainter p(&img);
    this->render(&p);
    img.save(path);
}

void MyGraphicsScene::renderToFile( const QString& path ){
    QImage img(outputSize,QImage::Format_RGB32);
    QPainter p(&img);
    this->render(&p);
    img.save(path);
}

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It should work regardless of the scene content.

[MadBear]

Greetings,

Thank you for your reply. I have used QGraphicsScene::render method, but this method is very slow, because I can't use shaders for OpenGL items (I need smoothing Gaussian filter for those items).

Thank you again,
Regards,
MadBear

[wysota]

I think you should use QGraphicsScene::render() to render to a GL pixel (or frame) buffer and then convert that to an image. This will allow you to use GL calls for rendering.

[MadBear]

Greetings,

I have tried this too. It doesn't work. But isn't this the same I already did in the first place?
Thank you for your help.

Regards,
MadBear

[wysota]

No, it's not the same. How does "doesn't work" manifest itself?