How to make QGraphicsItem a background for the QGraphicsScene?

[CassioTC]

I need use QGraphicsItem as a background, this background can be changed by the user any time.

In future I will add other items, like icons.

I'm using a 1680x1050 image, but will have to support any size.

My problem is: the image background being shown in diferent positions and sizes in FullScreen mode e maximized mode and in both cases with a wrong size and position.

mainview.h

MainView::MainView(QGraphicsView *parent)
    : QGraphicsView(parent)
{
    view = new QGraphicsView();
    scene = new QGraphicsScene(0,0,QApplication::desktop()->width(),QApplication::desktop()->height());
 
    Background *bg = new Background();
    scene->addItem(bg);
    setScene(scene);
 
    setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setViewportUpdateMode(FullViewportUpdate);
    setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform | QPainter::TextAntialiasing);
}
 
void MainView::resizeEvent(QResizeEvent *event)
{
    QGraphicsView::resizeEvent(event);
    fitInView(scene->sceneRect(), Qt::IgnoreAspectRatio);
    scene->setSceneRect(0,0, view->width(), view->height());
}

MainView::MainView(QGraphicsView *parent)
    : QGraphicsView(parent)
{
    view = new QGraphicsView();
    scene = new QGraphicsScene(0,0,QApplication::desktop()->width(),QApplication::desktop()->height());

    Background *bg = new Background();
    scene->addItem(bg);
    setScene(scene);

    setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setViewportUpdateMode(FullViewportUpdate);
    setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform | QPainter::TextAntialiasing);
}

void MainView::resizeEvent(QResizeEvent *event)
{
    QGraphicsView::resizeEvent(event);
    fitInView(scene->sceneRect(), Qt::IgnoreAspectRatio);
    scene->setSceneRect(0,0, view->width(), view->height());
}

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mainview.cpp

class MainView : public QGraphicsView
{
    Q_OBJECT
public:
    MainView(QGraphicsView *parent=0);
    ~MainView() {};
 
signals:
 
public slots:
 
private:
    QGraphicsView *view;
    QGraphicsScene *scene;
 
protected:
    void resizeEvent(QResizeEvent *event);
};

class MainView : public QGraphicsView
{
    Q_OBJECT
public:
    MainView(QGraphicsView *parent=0);
    ~MainView() {};

signals:

public slots:

private:
    QGraphicsView *view;
    QGraphicsScene *scene;

protected:
    void resizeEvent(QResizeEvent *event);
};

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background.h

class Background : public QGraphicsItem
{
public:
    Background(QGraphicsItem *parent=0);
 
    QRectF boundingRect() const
    {
        return QRectF(0,0,QApplication::desktop()->width(),QApplication::desktop()->height());
    }
 
private:
    QPixmap *backgroundImage;
 
protected:
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
    {
            painter->drawPixmap(boundingRect().toRect(),*backgroundImage);
    }
};

class Background : public QGraphicsItem
{
public:
    Background(QGraphicsItem *parent=0);

    QRectF boundingRect() const
    {
        return QRectF(0,0,QApplication::desktop()->width(),QApplication::desktop()->height());
    }

private:
    QPixmap *backgroundImage;

protected:
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
    {
            painter->drawPixmap(boundingRect().toRect(),*backgroundImage);
    }
};

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background.cpp

Background::Background(QGraphicsItem *parent)
{
    backgroundImage = new QPixmap();
    backgroundImage->load("C:/wallpaper.jpg");
}

Background::Background(QGraphicsItem *parent)
{
    backgroundImage = new QPixmap();
    backgroundImage->load("C:/wallpaper.jpg");
}

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[high_flyer]

You should not do that, as it makes no sense to have a top level item as background item.
The scene should provide the background, and it does.
See:
http://doc.qt.nokia.com/latest/qgrap...drawBackground
for more details.

[CassioTC]

Ok.

I comment this lines:

//Background *bg = new Background();
//scene->addItem(bg);
 
//setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform | QPainter::TextAntialiasing);
//scene->setSceneRect(0,0, view->width(), view->height());

//Background *bg = new Background();
//scene->addItem(bg);

//setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform | QPainter::TextAntialiasing);
//scene->setSceneRect(0,0, view->width(), view->height());

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and add this:

void MainView::drawBackground(QPainter *painter, const QRectF &rect)
{
    QImage img;
    img.load("C:/wallpaper.jpg");
 
    QRectF r;
    r.setRect(0,0,img.width(),img.height());
 
    painter->drawImage(r,img);
}

void MainView::drawBackground(QPainter *painter, const QRectF &rect)
{
    QImage img;
    img.load("C:/wallpaper.jpg");

    QRectF r;
    r.setRect(0,0,img.width(),img.height());

    painter->drawImage(r,img);
}

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But why is so slow??

[high_flyer]

because you load the image every time the background is being drawn.
Load the image somewhere else, store it in a member and use only the member in drawBackground()

[CassioTC]

Thank you.
Now works fine