(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.

 

• View a screenshot of 'CppQGraphicsObjectExample1' (png)
• Download the Qt Creator project 'CppQGraphicsObjectExample1' (zip)

Technical facts

 

Operating system(s) or programming environment(s)

• Lubuntu 15.04 (vivid)

IDE(s):

• Qt Creator 3.1.1

Project type:

• Console application

C++ standard:

• C++98

Compiler(s):

• G++ 4.9.2

Libraries used:

• STL: GNU ISO C++ Library, version 4.9.2

 

 

 

 

 

Qt project file: ./CppQGraphicsObjectExample1/CppQGraphicsObjectExample1.pro

 

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include(../../DesktopApplication.pri) SOURCES += \     qtmain.cpp \     qtwidget.cpp \     qtitem.cpp HEADERS += \     qtwidget.h \     qtitem.h RESOURCES += \     CppQGraphicsObjectExample1.qrc

 

 

 

 

 

./CppQGraphicsObjectExample1/qtitem.h

 

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#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

 

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#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

 

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#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

 

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#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

 

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#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); }