Basic Graphics Layouts Example

LayoutItem Class Implementation

In LayoutItem's constructor, m_pix is instantiated and the block.png image is loaded into it.

 LayoutItem::LayoutItem(QGraphicsItem *parent/* = 0*/)
     : QGraphicsLayoutItem(), QGraphicsItem(parent)
 {
     m_pix = new QPixmap(QLatin1String(":/images/block.png"));
     setGraphicsItem(this);
 }

We use the Q_UNUSED() macro to prevent the compiler from generating warnings regarding unused parameters.

 void LayoutItem::paint(QPainter *painter,
     const QStyleOptionGraphicsItem *option, QWidget *widget /*= 0*/)
 {
     Q_UNUSED(widget);
     Q_UNUSED(option);

     QRectF frame(QPointF(0,0), geometry().size());
     qreal w = m_pix->width();
     qreal h = m_pix->height();
     QGradientStops stops;

The idea behind the paint() function is to paint the background rect then paint a rect around the pixmap.

     // paint a background rect (with gradient)
     QLinearGradient gradient(frame.topLeft(), frame.topLeft() + QPointF(200,200));
     stops << QGradientStop(0.0, QColor(60, 60,  60));
     stops << QGradientStop(frame.height()/2/frame.height(), QColor(102, 176, 54));

     //stops << QGradientStop(((frame.height() + h)/2 )/frame.height(), QColor(157, 195,  55));
     stops << QGradientStop(1.0, QColor(215, 215, 215));
     gradient.setStops(stops);
     painter->setBrush(QBrush(gradient));
     painter->drawRoundedRect(frame, 10.0, 10.0);

     // paint a rect around the pixmap (with gradient)
     QPointF pixpos = frame.center() - (QPointF(w, h)/2);
     QRectF innerFrame(pixpos, QSizeF(w, h));
     innerFrame.adjust(-4, -4, +4, +4);
     gradient.setStart(innerFrame.topLeft());
     gradient.setFinalStop(innerFrame.bottomRight());
     stops.clear();
     stops << QGradientStop(0.0, QColor(215, 255, 200));
     stops << QGradientStop(0.5, QColor(102, 176, 54));
     stops << QGradientStop(1.0, QColor(0, 0,  0));
     gradient.setStops(stops);
     painter->setBrush(QBrush(gradient));
     painter->drawRoundedRect(innerFrame, 10.0, 10.0);
     painter->drawPixmap(pixpos, *m_pix);
 }

The reimplementation of boundingRect() will set the top left corner at (0,0), and the size of it will be the size of the layout items geometry(). This is the area that we paint within.

 QRectF LayoutItem::boundingRect() const
 {
     return QRectF(QPointF(0,0), geometry().size());
 }

The reimplementation of setGeometry() simply calls its baseclass implementation. However, since this will change the boundingRect we must also call prepareGeometryChange(). Finally, we move the item according to geom.topLeft().

 void LayoutItem::setGeometry(const QRectF &geom)
 {
     prepareGeometryChange();
     QGraphicsLayoutItem::setGeometry(geom);
     setPos(geom.topLeft());
 }

Since we don't want the size of the item to be smaller than the pixmap, we must make sure that we return a size hint that is larger than m_pix. We also add some extra space around for borders that we will paint later. Alternatively, you could scale the pixmap to prevent the item from becoming smaller than the pixmap. The preferred size is the same as the minimum size hint, while we set maximum to be a large value

 QSizeF LayoutItem::sizeHint(Qt::SizeHint which, const QSizeF &constraint) const
 {
     switch (which) {
     case Qt::MinimumSize:
     case Qt::PreferredSize:
         // Do not allow a size smaller than the pixmap with two frames around it.
         return m_pix->size() + QSize(12, 12);
     case Qt::MaximumSize:
         return QSizeF(1000,1000);
     default:
         break;
     }
     return constraint;
 }