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coloritem.cpp Example File
graphicsview/dragdroprobot/coloritem.cpp

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 #include <QtGui>

 #include "coloritem.h"

 ColorItem::ColorItem()
     : color(qrand() % 256, qrand() % 256, qrand() % 256)
 {
     setToolTip(QString("QColor(%1, %2, %3)\n%4")
               .arg(color.red()).arg(color.green()).arg(color.blue())
               .arg("Click and drag this color onto the robot!"));
     setCursor(Qt::OpenHandCursor);
 }

 QRectF ColorItem::boundingRect() const
 {
     return QRectF(-15.5, -15.5, 34, 34);
 }

 void ColorItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
 {
     Q_UNUSED(option);
     Q_UNUSED(widget);
     painter->setPen(Qt::NoPen);
     painter->setBrush(Qt::darkGray);
     painter->drawEllipse(-12, -12, 30, 30);
     painter->setPen(QPen(Qt::black, 1));
     painter->setBrush(QBrush(color));
     painter->drawEllipse(-15, -15, 30, 30);
 }

 void ColorItem::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
     if (event->button() != Qt::LeftButton) {
         event->ignore();
         return;
     }

     setCursor(Qt::ClosedHandCursor);
 }

 void ColorItem::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
 {
     if (QLineF(event->screenPos(), event->buttonDownScreenPos(Qt::LeftButton))
         .length() < QApplication::startDragDistance()) {
         return;
     }

     QDrag *drag = new QDrag(event->widget());
     QMimeData *mime = new QMimeData;
     drag->setMimeData(mime);

     static int n = 0;
     if (n++ > 2 && (qrand() % 3) == 0) {
         QImage image(":/images/head.png");
         mime->setImageData(image);

         drag->setPixmap(QPixmap::fromImage(image).scaled(30, 40));
         drag->setHotSpot(QPoint(15, 30));
     } else {
         mime->setColorData(color);
         mime->setText(QString("#%1%2%3")
                       .arg(color.red(), 2, 16, QLatin1Char('0'))
                       .arg(color.green(), 2, 16, QLatin1Char('0'))
                       .arg(color.blue(), 2, 16, QLatin1Char('0')));

         QPixmap pixmap(34, 34);
         pixmap.fill(Qt::white);

         QPainter painter(&pixmap);
         painter.translate(15, 15);
         painter.setRenderHint(QPainter::Antialiasing);
         paint(&painter, 0, 0);
         painter.end();

         pixmap.setMask(pixmap.createHeuristicMask());

         drag->setPixmap(pixmap);
         drag->setHotSpot(QPoint(15, 20));
     }

     drag->exec();
     setCursor(Qt::OpenHandCursor);
 }

 void ColorItem::mouseReleaseEvent(QGraphicsSceneMouseEvent *)
 {
     setCursor(Qt::OpenHandCursor);
 }