Show background image to QGraphicsView

[franco.amato]

Good morning,
I would have a help in showing a background image to a QGraphicsView.
I have an app develop to edit images and before displaying the images that have to be edited I would display a logo.

Reading docs I think to use the QGraphicsView::drawBackground so in brief this is what I did

// Ctor of my class derived from QGraphicsView
PageView::PageView(QWidget *parent) : QGraphicsView(parent)
{
  // ...
  // more code
  if ( m_logoPixmap.load(":/Resources/Logos/editor_logo_v.png"))
    {
      // scale it
      m_logoScaledPixmap = m_logoPixmap.scaled(QSize(viewport()->width() / 3, viewport()->height() / 3), Qt::KeepAspectRatio, Qt::SmoothTransformation); // Incorrect size
    }
}

// Ctor of my class derived from QGraphicsView
PageView::PageView(QWidget *parent) : QGraphicsView(parent)
{
  // ...
  // more code
  if ( m_logoPixmap.load(":/Resources/Logos/editor_logo_v.png"))
    {
      // scale it
      m_logoScaledPixmap = m_logoPixmap.scaled(QSize(viewport()->width() / 3, viewport()->height() / 3), Qt::KeepAspectRatio, Qt::SmoothTransformation); // Incorrect size
    }
}

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I would scale it to be a percentage of the view but i can not get the correct size ( I always get 100, 30 )

// Here I would show the logo
void PageView::drawBackground(QPainter *painter, const QRectF &rect)
{
      QRectF pixmapBoundingRect = m_logoScaledPixmap.rect();
      qreal maxValue = qMax(pixmapBoundingRect.width(), pixmapBoundingRect.height());
 
      painter->drawPixmap(pixmapBoundingRect, m_logoScaledPixmap, QRect(0.0, 0.0, m_logoScaledPixmap.width(), m_logoScaledPixmap.height())); // Not centered
}

// Here I would show the logo
void PageView::drawBackground(QPainter *painter, const QRectF &rect)
{
      QRectF pixmapBoundingRect = m_logoScaledPixmap.rect();
      qreal maxValue = qMax(pixmapBoundingRect.width(), pixmapBoundingRect.height());

      painter->drawPixmap(pixmapBoundingRect, m_logoScaledPixmap, QRect(0.0, 0.0, m_logoScaledPixmap.width(), m_logoScaledPixmap.height())); // Not centered
}

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I would the logo to be centered and is also pixeled when scaled even adding Qt::SmoothTransformation ( its original size is 2000 * 2000 pixels ).
I also would the logo to disappear when I load images to be edited

Thanx

[Santosh Reddy]

Hope this helps

class GraphicsView : public QGraphicsView
{
public:
    explicit GraphicsView(const QImage & background, QWidget * parent = 0)
        : QGraphicsView(parent)
        , mImage(background){ }
 
protected:
    void paintEvent(QPaintEvent * event) override
    {
        QPainter painter(viewport());
        const QImage image = mImage.scaled(viewport()->size()/3);
        const QPoint point = viewport()->rect().center() - QPoint(image.width()/2, image.height()/2);
        painter.drawImage(point, image);
        QGraphicsView::paintEvent(event);
    }
 
private:
    const QImage mImage;
};

class GraphicsView : public QGraphicsView
{
public:
    explicit GraphicsView(const QImage & background, QWidget * parent = 0)
        : QGraphicsView(parent)
        , mImage(background){ }

protected:
    void paintEvent(QPaintEvent * event) override
    {
        QPainter painter(viewport());
        const QImage image = mImage.scaled(viewport()->size()/3);
        const QPoint point = viewport()->rect().center() - QPoint(image.width()/2, image.height()/2);
        painter.drawImage(point, image);
        QGraphicsView::paintEvent(event);
    }

private:
    const QImage mImage;
};

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[franco.amato]

Hi thank you so much for your reply, but unfortunately it does not solve my problem.

I got a working solution in this way:

void PageView::drawBackground(QPainter *painter, const QRectF &rect)
{
  QRectF imageBoundingRect = m_scaledLogoImage.rect();
  QRectF target(QPoint(-200,-200),QSize(imageBoundingRect.width(), imageBoundingRect.height())); // Considering the size of the image is 400*400
 
  painter->save();
  painter->drawImage(target, m_scaledLogoImage);
  painter->restore();
}

void PageView::drawBackground(QPainter *painter, const QRectF &rect)
{
  QRectF imageBoundingRect = m_scaledLogoImage.rect();
  QRectF target(QPoint(-200,-200),QSize(imageBoundingRect.width(), imageBoundingRect.height())); // Considering the size of the image is 400*400
  
  painter->save();
  painter->drawImage(target, m_scaledLogoImage);
  painter->restore();
}

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I have another question. I resize the image in the ctor of the class

if (m_logoImage.load(":/Resources/editor_logo_v.png");
{
  m_scaledLogoImage = m_logoImage.scaled(QSize(400,400), Qt::KeepAspectRatio, Qt::SmoothTransformation);
}

if (m_logoImage.load(":/Resources/editor_logo_v.png");
{
  m_scaledLogoImage = m_logoImage.scaled(QSize(400,400), Qt::KeepAspectRatio, Qt::SmoothTransformation);
}

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and I have to rescale to a fixed size but I would rescale to a percentage of the view and I can not because the size() always returns (100, 30)

Do you have any idea why?

Thank you