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(C++) QGraphicsObjectExample1

 

QGraphicsObject example 1: basic is a QGraphicsObject example. Actually, it is not so basic, as it is a conversion from QGraphicsPixmapItem example 4: pixmap that changes cursor, where the QGraphicsPixmapItem is replaced by a QGraphicsObject.

 

Technical facts

 

Operating system(s) or programming environment(s)

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Qt project file: ./CppQGraphicsObjectExample1/CppQGraphicsObjectExample1.pro

 

include(../../DesktopApplication.pri)

SOURCES += \
    qtmain.cpp \
    qtwidget.cpp \
    qtitem.cpp

HEADERS += \
    qtwidget.h \
    qtitem.h

RESOURCES += \
    CppQGraphicsObjectExample1.qrc

 

 

 

 

 

./CppQGraphicsObjectExample1/qtitem.h

 

#ifndef QTITEM_H
#define QTITEM_H

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Weffc++"
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
#pragma GCC diagnostic ignored "-Wunused-but-set-parameter"
#include <QGraphicsObject>
#include <boost/signals2.hpp>
#pragma GCC diagnostic pop

//Forward declaration
struct QPixmap;

///A QGraphicsObject that
/// - loads its pixmap from resources
/// - is clickable
/// - is movable
/// - changes the cursor
class QtItem : public QGraphicsObject
{
  Q_OBJECT

  public:

  QtItem(QGraphicsItem *parent = 0);

  ///Signal emitted when clicked
  boost::signals2::signal<void (QtItem*)> m_clicked_signal;

  protected:
  void mousePressEvent(QGraphicsSceneMouseEvent *event);

  void hoverMoveEvent(QGraphicsSceneHoverEvent *event);

  QRectF boundingRect() const;

  void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);

  private:
  ///The pixmap
  boost::scoped_ptr<QPixmap> m_pixmap;
};

#endif // QTITEM_H

 

 

 

 

 

./CppQGraphicsObjectExample1/qtitem.cpp

 

#include <cassert>

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Weffc++"
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
#pragma GCC diagnostic ignored "-Wunused-but-set-parameter"
#include <QCursor>
#include <QPainter>
#include <QPixmap>
#include "qtitem.h"
#pragma GCC diagnostic pop

QtItem::QtItem(QGraphicsItem *parent)
  : QGraphicsObject(parent),
    m_clicked_signal{},
    m_pixmap{new QPixmap(":/images/PicR.png")}
{
  assert(!m_pixmap->isNull()
    && "Assume pixmap is loaded successfully");

  this->setFlags(
      QGraphicsItem::ItemIsMovable
    | QGraphicsItem::ItemIsSelectable
  );


  //Without this line, hoverMoveEvent will not be called
  this->setAcceptHoverEvents(true);
}

QRectF QtItem::boundingRect() const
{
  const QRectF targetRect = m_pixmap->rect().translated(-m_pixmap->rect().center());
  assert(targetRect.center().x() >= -1.0);
  assert(targetRect.center().x() <=  1.0);
  assert(targetRect.center().y() >= -1.0);
  assert(targetRect.center().y() <=  1.0);
  return targetRect;
}

void QtItem::hoverMoveEvent(QGraphicsSceneHoverEvent *)
{
  this->setCursor(QCursor(Qt::PointingHandCursor));
}

void QtItem::mousePressEvent(QGraphicsSceneMouseEvent *)
{
  //Emit the Boost signal
  m_clicked_signal(this);
}

void QtItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)
{
  const QRectF targetRect = m_pixmap->rect().translated(-m_pixmap->rect().center());
  assert(targetRect.center().x() >= -1.0);
  assert(targetRect.center().x() <=  1.0);
  assert(targetRect.center().y() >= -1.0);
  assert(targetRect.center().y() <=  1.0);

  painter->drawPixmap(targetRect,*m_pixmap,m_pixmap->rect());

  //Draw a thick red line around the pixmap when it is selected
  if (this->isSelected())
  {
    painter->setPen(QPen(QColor(255,0,0),2));
    painter->drawRect(this->boundingRect().adjusted(2.0,2.0,-2.0,-2.0));
  }
}

 

 

 

 

 

./CppQGraphicsObjectExample1/qtmain.cpp

 

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Weffc++"
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
#pragma GCC diagnostic ignored "-Wunused-but-set-parameter"
#include <QApplication>
#include "qtwidget.h"
#pragma GCC diagnostic pop

int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  QtWidget w;
  w.setGeometry(100,100,400,400);
  w.show();
  return a.exec();
}

 

 

 

 

 

./CppQGraphicsObjectExample1/qtwidget.h

 

#ifndef QTWIDGET_H
#define QTWIDGET_H

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Weffc++"
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
#pragma GCC diagnostic ignored "-Wunused-but-set-parameter"
#include <QGraphicsView>
#pragma GCC diagnostic pop

struct QtItem;

struct QtWidget : public QGraphicsView
{
  QtWidget();

  ///Respond to a click on a QtItem
  void OnItemClick(QtItem * const item);
};

#endif // QTWIDGET_H

 

 

 

 

 

./CppQGraphicsObjectExample1/qtwidget.cpp

 

#include <cassert>

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Weffc++"
#pragma GCC diagnostic ignored "-Wunused-local-typedefs"
#pragma GCC diagnostic ignored "-Wunused-but-set-parameter"
#include <boost/bind.hpp>
#include <boost/lambda/bind.hpp>

#include <QGraphicsScene>
#include <QGraphicsPixmapItem>

#include "qtitem.h"
#include "qtwidget.h"
#pragma GCC diagnostic pop

QtWidget::QtWidget()
{
  QGraphicsScene * const scene = new QGraphicsScene(this);
  this->setScene(scene);

  const int n_items = 64;
  for (int i=0; i!=n_items; ++i)
  {
    QtItem * const item = new QtItem;
    item->m_clicked_signal.connect(
      boost::bind(
        &QtWidget::OnItemClick,this, boost::lambda::_1));
    //Scatter those items around a bit
    item->setPos(
      - 128 + (std::rand() % 256),
      - 128 + (std::rand() % 256));

    scene->addItem(item);
  }
}

void QtWidget::OnItemClick(QtItem * const item)
{
  item->setRotation( item->rotation() + 15.0);
}

 

 

 

 

 

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