paintEvent on QGraphicsScene?

[sergio87]

Hi!

I'm trying to make a program that draws a ellipse over an image when you click. I¡ll explain:

I open an image with QGraphicsScene (subclassed). In the subclass I override the mouseReleaseEvent to collect the mouse clicks. I want to draw an ellipse when click the mouse in these coordinates. The coordinates are from the image and not from the window.

This is the code, based on a example of QT:
SubQGraphicsScene.cpp

SubQGraphicsScene::SubQGraphicsScene(QObject *parent)
	: QGraphicsScene(parent)
{
	// TODO Auto-generated constructor stub
}
 
SubQGraphicsScene::~SubQGraphicsScene() {
	// TODO Auto-generated destructor stub
}
 
void SubQGraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{
	ultimo_x = event->scenePos().x();
	ultimo_y = event->scenePos().y();
	if (event->button()  == Qt::LeftButton){
		cout << "Right button :" << ultimo_x << ", " << ultimo_y << endl;
	}else{
		cout << "Left button :" << ultimo_x << ", " << ultimo_y  << endl;
	}
	update();
	this->update();
}
 
void SubQGraphicsScene::paintEvent(QPaintEvent *event){
	cout << "PAINTER" << endl;
	//QGraphicsScene::paintEvent(event);
	//painter.begin(this);
	painter.setPen(QColor("#FF0000"));
	//painter.setBrush(QColor("#FFAAAA"));
	//Draw reference points
	painter.drawEllipse(ultimo_x,ultimo_y,20,20);
	//Draw points
	painter.end();	// close the painter
}

SubQGraphicsScene::SubQGraphicsScene(QObject *parent)
	: QGraphicsScene(parent)
{
	// TODO Auto-generated constructor stub
}

SubQGraphicsScene::~SubQGraphicsScene() {
	// TODO Auto-generated destructor stub
}

void SubQGraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{
	ultimo_x = event->scenePos().x();
	ultimo_y = event->scenePos().y();
	if (event->button()  == Qt::LeftButton){
		cout << "Right button :" << ultimo_x << ", " << ultimo_y << endl;
	}else{
		cout << "Left button :" << ultimo_x << ", " << ultimo_y  << endl;
	}
	update();
	this->update();
}

void SubQGraphicsScene::paintEvent(QPaintEvent *event){
	cout << "PAINTER" << endl;
	//QGraphicsScene::paintEvent(event);
	//painter.begin(this);
	painter.setPen(QColor("#FF0000"));
	//painter.setBrush(QColor("#FFAAAA"));
	//Draw reference points
	painter.drawEllipse(ultimo_x,ultimo_y,20,20);
	//Draw points
	painter.end();	// close the painter
}

To copy to clipboard, switch view to plain text mode 

SubQGraphicsScene.h:

#ifndef SUBQGRAPHICSSCENE_H_
#define SUBQGRAPHICSSCENE_H_
#include <QGraphicsScene>
#include <QPainter>
#include <QtGui>
 
QT_BEGIN_NAMESPACE
class QPaintEvent;
QT_END_NAMESPACE
 
class SubQGraphicsScene : public QGraphicsScene
{
	Q_OBJECT
public:
	SubQGraphicsScene(QObject *parent = 0);
	virtual ~SubQGraphicsScene();
 
private:
	void mouseReleaseEvent(QGraphicsSceneMouseEvent* event);
	QPainter painter;
	int ultimo_x;
	int ultimo_y;
 
protected:
	void paintEvent(QPaintEvent *event);
};
 
#endif /* SUBQGRAPHICSSCENE_H_ */

#ifndef SUBQGRAPHICSSCENE_H_
#define SUBQGRAPHICSSCENE_H_
#include <QGraphicsScene>
#include <QPainter>
#include <QtGui>

QT_BEGIN_NAMESPACE
class QPaintEvent;
QT_END_NAMESPACE

class SubQGraphicsScene : public QGraphicsScene
{
	Q_OBJECT
public:
	SubQGraphicsScene(QObject *parent = 0);
	virtual ~SubQGraphicsScene();

private:
	void mouseReleaseEvent(QGraphicsSceneMouseEvent* event);
	QPainter painter;
	int ultimo_x;
	int ultimo_y;

protected:
	void paintEvent(QPaintEvent *event);
};

#endif /* SUBQGRAPHICSSCENE_H_ */

To copy to clipboard, switch view to plain text mode 

SvgView.cpp:

SvgView::SvgView(QWidget *parent)
    : QGraphicsView(parent)
    , m_renderer(Native)
    , m_svgItem(0)
    , m_backgroundItem(0)
    , m_outlineItem(0)
{
	mScene = new SubQGraphicsScene(this);
    setScene(mScene);
    setTransformationAnchor(AnchorUnderMouse);
    setDragMode(RubberBandDrag);
    setViewportUpdateMode(FullViewportUpdate);
 
    // Prepare background check-board pattern
    QPixmap tilePixmap(64, 64);
    tilePixmap.fill(Qt::white);
    QPainter tilePainter(&tilePixmap);
    QColor color(220, 220, 220);
    tilePainter.fillRect(0, 0, 32, 32, color);
    tilePainter.fillRect(32, 32, 32, 32, color);
    tilePainter.end();
 
    factor = 1.0;
 
    setBackgroundBrush(tilePixmap);
}
 
void SvgView::drawBackground(QPainter *p, const QRectF &)
{
    p->save();
    p->resetTransform();
    p->drawTiledPixmap(viewport()->rect(), backgroundBrush().texture());
    p->restore();
}
 
void SvgView::openFile(const QFile &file)
{
    if (!file.exists())
        return;
    //QGraphicsScene *s = scene();
 
    mScene->clear();
    resetTransform();
 
    QPixmap pix( "C:\\i3s\\FotosINPUT\\prueba.JPG" );
    mScene->addPixmap(pix);
    mScene->update();
}
 
void SvgView::setRenderer(RendererType type)
{
    m_renderer = type;
 
    if (m_renderer == OpenGL) {
#ifndef QT_NO_OPENGL
        setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
#endif
    } else {
        setViewport(new QWidget);
    }
}
 
void SvgView::setHighQualityAntialiasing(bool highQualityAntialiasing)
{
#ifndef QT_NO_OPENGL
    setRenderHint(QPainter::HighQualityAntialiasing, highQualityAntialiasing);
#else
    Q_UNUSED(highQualityAntialiasing);
#endif
}
 
void SvgView::setViewBackground(bool enable)
{
    if (!m_backgroundItem)
          return;
 
    m_backgroundItem->setVisible(enable);
}
 
void SvgView::setViewOutline(bool enable)
{
    if (!m_outlineItem)
        return;
 
    m_outlineItem->setVisible(enable);
}
 
void SvgView::paintEvent(QPaintEvent *event)
{
    if (m_renderer == Image) {
        if (m_image.size() != viewport()->size()) {
            m_image = QImage(viewport()->size(), QImage::Format_ARGB32_Premultiplied);
        }
 
        QPainter imagePainter(&m_image);
        QGraphicsView::render(&imagePainter);
        imagePainter.end();
 
        QPainter p(viewport());
        p.drawImage(0, 0, m_image);
 
    } else {
        QGraphicsView::paintEvent(event);
		painter.begin(this);
		painter.setPen(QColor("#FF0000"));
		painter.drawEllipse(100,100,20,20);
		painter.end();	// close the painter
    }
}
 
void SvgView::wheelEvent(QWheelEvent *event)
{
    if(event->delta()>0){
    	scale(1.25, 1.25);
    	factor += 0.25; //Save the scale
    }else{
	scale(0.75, 0.75);
	factor -= 0.25; //Save the scale
    }
    event->accept();
}

SvgView::SvgView(QWidget *parent)
    : QGraphicsView(parent)
    , m_renderer(Native)
    , m_svgItem(0)
    , m_backgroundItem(0)
    , m_outlineItem(0)
{
	mScene = new SubQGraphicsScene(this);
    setScene(mScene);
    setTransformationAnchor(AnchorUnderMouse);
    setDragMode(RubberBandDrag);
    setViewportUpdateMode(FullViewportUpdate);

    // Prepare background check-board pattern
    QPixmap tilePixmap(64, 64);
    tilePixmap.fill(Qt::white);
    QPainter tilePainter(&tilePixmap);
    QColor color(220, 220, 220);
    tilePainter.fillRect(0, 0, 32, 32, color);
    tilePainter.fillRect(32, 32, 32, 32, color);
    tilePainter.end();

    factor = 1.0;

    setBackgroundBrush(tilePixmap);
}

void SvgView::drawBackground(QPainter *p, const QRectF &)
{
    p->save();
    p->resetTransform();
    p->drawTiledPixmap(viewport()->rect(), backgroundBrush().texture());
    p->restore();
}

void SvgView::openFile(const QFile &file)
{
    if (!file.exists())
        return;
    //QGraphicsScene *s = scene();

    mScene->clear();
    resetTransform();

    QPixmap pix( "C:\\i3s\\FotosINPUT\\prueba.JPG" );
    mScene->addPixmap(pix);
    mScene->update();
}

void SvgView::setRenderer(RendererType type)
{
    m_renderer = type;

    if (m_renderer == OpenGL) {
#ifndef QT_NO_OPENGL
        setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
#endif
    } else {
        setViewport(new QWidget);
    }
}

void SvgView::setHighQualityAntialiasing(bool highQualityAntialiasing)
{
#ifndef QT_NO_OPENGL
    setRenderHint(QPainter::HighQualityAntialiasing, highQualityAntialiasing);
#else
    Q_UNUSED(highQualityAntialiasing);
#endif
}

void SvgView::setViewBackground(bool enable)
{
    if (!m_backgroundItem)
          return;

    m_backgroundItem->setVisible(enable);
}

void SvgView::setViewOutline(bool enable)
{
    if (!m_outlineItem)
        return;

    m_outlineItem->setVisible(enable);
}

void SvgView::paintEvent(QPaintEvent *event)
{
    if (m_renderer == Image) {
        if (m_image.size() != viewport()->size()) {
            m_image = QImage(viewport()->size(), QImage::Format_ARGB32_Premultiplied);
        }

        QPainter imagePainter(&m_image);
        QGraphicsView::render(&imagePainter);
        imagePainter.end();

        QPainter p(viewport());
        p.drawImage(0, 0, m_image);

    } else {
        QGraphicsView::paintEvent(event);
		painter.begin(this);
		painter.setPen(QColor("#FF0000"));
		painter.drawEllipse(100,100,20,20);
		painter.end();	// close the painter
    }
}

void SvgView::wheelEvent(QWheelEvent *event)
{
    if(event->delta()>0){
    	scale(1.25, 1.25);
    	factor += 0.25; //Save the scale
    }else{
	scale(0.75, 0.75);
	factor -= 0.25; //Save the scale
    }
    event->accept();
}

To copy to clipboard, switch view to plain text mode 

SvgView.h:

class SvgView : public QGraphicsView
{
    Q_OBJECT
 
public:
    enum RendererType { Native, OpenGL, Image };
 
    SvgView(QWidget *parent = 0);
 
    void openFile(const QFile &file);
    void setRenderer(RendererType type = Native);
    void drawBackground(QPainter *p, const QRectF &rect);
    void mousePressEvent(QMouseEvent *event);
 
public slots:
    void setHighQualityAntialiasing(bool highQualityAntialiasing);
    void setViewBackground(bool enable);
    void setViewOutline(bool enable);
 
protected:
    void wheelEvent(QWheelEvent *event);
    void paintEvent(QPaintEvent *event);
 
private:
    RendererType m_renderer;
 
    QGraphicsItem *m_svgItem;
    QGraphicsRectItem *m_backgroundItem;
    QGraphicsRectItem *m_outlineItem;
 
    qreal factor;
    SubQGraphicsScene *mScene;
    QPainter painter;
    QImage m_image;
};

class SvgView : public QGraphicsView
{
    Q_OBJECT

public:
    enum RendererType { Native, OpenGL, Image };

    SvgView(QWidget *parent = 0);

    void openFile(const QFile &file);
    void setRenderer(RendererType type = Native);
    void drawBackground(QPainter *p, const QRectF &rect);
    void mousePressEvent(QMouseEvent *event);

public slots:
    void setHighQualityAntialiasing(bool highQualityAntialiasing);
    void setViewBackground(bool enable);
    void setViewOutline(bool enable);

protected:
    void wheelEvent(QWheelEvent *event);
    void paintEvent(QPaintEvent *event);

private:
    RendererType m_renderer;

    QGraphicsItem *m_svgItem;
    QGraphicsRectItem *m_backgroundItem;
    QGraphicsRectItem *m_outlineItem;

    qreal factor;
    SubQGraphicsScene *mScene;
    QPainter painter;
    QImage m_image;
};

To copy to clipboard, switch view to plain text mode 

It never draws an ellipse. SubQGraphicsScene:aintEvent never is called. SvgView:aintEvent is called, but not draw...

Can anyone help me, please!

Thanks in advance

[wysota]

QGraphicsScene doesn't have a paintEvent so it's not suprising your implementation of this method is not called.

[sergio87]

Thanks!!

So, how can I paint over the image?

Another question, why QGraphicsView doesn't paint?

Thanks a lot!

[wysota]

So, how can I paint over the image?

You can paint on the viewport of the view, you can paint on the item or you can add an item to the scene. All depends on the effect you want to achieve.

Another question, why QGraphicsView doesn't paint?

You are probably opening the painter on the view and not its viewport.

[sergio87]

Lots of thanks!

You can paint on the viewport of the view, you can paint on the item or you can add an item to the scene. All depends on the effect you want to achieve.

I'll try to add an item to the scene. Because in the future I would like to paint a lot of points (and that points will be in a file). I'll post the results!

Thanks a lot!!

[sergio87]

I solved it:

- FIRST solution:

void SubQGraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{
	ultimo_x = event->scenePos().x();
	ultimo_y = event->scenePos().y();
	if (event->button()  == Qt::LeftButton){
		cout << "Right button :" << ultimo_x << ", " << ultimo_y << endl;
	}else{
		cout << "Left button :" << ultimo_x << ", " << ultimo_y  << endl;
	}
	addEllipse(ultimo_x-10,ultimo_y-10,20,20);
}

void SubQGraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{
	ultimo_x = event->scenePos().x();
	ultimo_y = event->scenePos().y();
	if (event->button()  == Qt::LeftButton){
		cout << "Right button :" << ultimo_x << ", " << ultimo_y << endl;
	}else{
		cout << "Left button :" << ultimo_x << ", " << ultimo_y  << endl;
	}
	addEllipse(ultimo_x-10,ultimo_y-10,20,20);
}

To copy to clipboard, switch view to plain text mode 

This code draw a ellipse when you click the mouse. This solution is very basic, but it works fine!

- SECOND solution:
For my interest, I subclassed QGraphicsItem and I paint in this class. Then I added it to the scene. It works perfect because I can draw a lot of things (ellipse, lines, etc). And is automatically scaled!

If some has the same problem as me, there is the full code:
svgView.cpp:

#include "svgview.h"
#include <QFile>
#include <QWheelEvent>
#include <QMouseEvent>
#include <QGraphicsRectItem>
#include <QGraphicsSvgItem>
#include <QPaintEvent>
#include <qmath.h>
#include <iostream>
using namespace std;
 
#ifndef QT_NO_OPENGL
#include <QGLWidget>
#endif
 
SvgView::SvgView(QWidget *parent)
    : QGraphicsView(parent)
    , m_renderer(Native)
    , m_svgItem(0)
    , m_backgroundItem(0)
    , m_outlineItem(0)
{
	mScene = new SubQGraphicsScene(this);
    setScene(mScene);
    setTransformationAnchor(AnchorUnderMouse);
    setDragMode(RubberBandDrag);
    setViewportUpdateMode(FullViewportUpdate);
 
    // Prepare background check-board pattern
    QPixmap tilePixmap(64, 64);
    tilePixmap.fill(Qt::white);
    QPainter tilePainter(&tilePixmap);
    QColor color(220, 220, 220);
    tilePainter.fillRect(0, 0, 32, 32, color);
    tilePainter.fillRect(32, 32, 32, 32, color);
    tilePainter.end();
 
    factor = 1.0;
    setBackgroundBrush(tilePixmap);
}
 
void SvgView::drawBackground(QPainter *p, const QRectF &)
{
    p->save();
    p->resetTransform();
    p->drawTiledPixmap(viewport()->rect(), backgroundBrush().texture());
    p->restore();
}
 
void SvgView::openFile(const QFile &file)
{
    if (!file.exists())
        return;
    //QGraphicsScene *s = scene();
 
    mScene->clear();
    resetTransform();
 
    QPixmap pix( "C:\\i3s\\FotosINPUT\\prueba.JPG" );
    mScene->addPixmap(pix);
    mScene->update();
    fpPaint = new FingerPrintPainter(mScene->sceneRect());
    mScene->addItem(fpPaint);
}
 
void SvgView::setRenderer(RendererType type)
{
    m_renderer = type;
 
    if (m_renderer == OpenGL) {
#ifndef QT_NO_OPENGL
        setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
#endif
    } else {
        setViewport(new QWidget);
    }
}
 
void SvgView::setHighQualityAntialiasing(bool highQualityAntialiasing)
{
#ifndef QT_NO_OPENGL
    setRenderHint(QPainter::HighQualityAntialiasing, highQualityAntialiasing);
#else
    Q_UNUSED(highQualityAntialiasing);
#endif
}
 
void SvgView::wheelEvent(QWheelEvent *event)
{
    if(event->delta()>0){
    	scale(1.25, 1.25);
    	factor += 0.25;
	 }else{
		 scale(0.75, 0.75);
		 factor -= 0.25;
	 }
    event->accept();
}

#include "svgview.h"
#include <QFile>
#include <QWheelEvent>
#include <QMouseEvent>
#include <QGraphicsRectItem>
#include <QGraphicsSvgItem>
#include <QPaintEvent>
#include <qmath.h>
#include <iostream>
using namespace std;

#ifndef QT_NO_OPENGL
#include <QGLWidget>
#endif

SvgView::SvgView(QWidget *parent)
    : QGraphicsView(parent)
    , m_renderer(Native)
    , m_svgItem(0)
    , m_backgroundItem(0)
    , m_outlineItem(0)
{
	mScene = new SubQGraphicsScene(this);
    setScene(mScene);
    setTransformationAnchor(AnchorUnderMouse);
    setDragMode(RubberBandDrag);
    setViewportUpdateMode(FullViewportUpdate);

    // Prepare background check-board pattern
    QPixmap tilePixmap(64, 64);
    tilePixmap.fill(Qt::white);
    QPainter tilePainter(&tilePixmap);
    QColor color(220, 220, 220);
    tilePainter.fillRect(0, 0, 32, 32, color);
    tilePainter.fillRect(32, 32, 32, 32, color);
    tilePainter.end();

    factor = 1.0;
    setBackgroundBrush(tilePixmap);
}

void SvgView::drawBackground(QPainter *p, const QRectF &)
{
    p->save();
    p->resetTransform();
    p->drawTiledPixmap(viewport()->rect(), backgroundBrush().texture());
    p->restore();
}

void SvgView::openFile(const QFile &file)
{
    if (!file.exists())
        return;
    //QGraphicsScene *s = scene();

    mScene->clear();
    resetTransform();

    QPixmap pix( "C:\\i3s\\FotosINPUT\\prueba.JPG" );
    mScene->addPixmap(pix);
    mScene->update();
    fpPaint = new FingerPrintPainter(mScene->sceneRect());
    mScene->addItem(fpPaint);
}

void SvgView::setRenderer(RendererType type)
{
    m_renderer = type;

    if (m_renderer == OpenGL) {
#ifndef QT_NO_OPENGL
        setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
#endif
    } else {
        setViewport(new QWidget);
    }
}

void SvgView::setHighQualityAntialiasing(bool highQualityAntialiasing)
{
#ifndef QT_NO_OPENGL
    setRenderHint(QPainter::HighQualityAntialiasing, highQualityAntialiasing);
#else
    Q_UNUSED(highQualityAntialiasing);
#endif
}

void SvgView::wheelEvent(QWheelEvent *event)
{
    if(event->delta()>0){
    	scale(1.25, 1.25);
    	factor += 0.25;
	 }else{
		 scale(0.75, 0.75);
		 factor -= 0.25;
	 }
    event->accept();
}

To copy to clipboard, switch view to plain text mode 

svgView.h:

#ifndef SVGVIEW_H
#define SVGVIEW_H
 
#include <QGraphicsView>
#include <QPainter>
#include "SubQGraphicsScene.h"
#include "FingerPrintPainter.h"
 
QT_BEGIN_NAMESPACE
class QWheelEvent;
class QPaintEvent;
class QFile;
QT_END_NAMESPACE
 
class SvgView : public QGraphicsView
{
    Q_OBJECT
 
public:
    enum RendererType { Native, OpenGL, Image };
 
    SvgView(QWidget *parent = 0);
 
    void openFile(const QFile &file);
    void setRenderer(RendererType type = Native);
    void drawBackground(QPainter *p, const QRectF &rect);
 
public slots:
    void setHighQualityAntialiasing(bool highQualityAntialiasing);
 
protected:
    void wheelEvent(QWheelEvent *event);
 
private:
    RendererType m_renderer;
 
    QGraphicsItem *m_svgItem;
    QGraphicsRectItem *m_backgroundItem;
    QGraphicsRectItem *m_outlineItem;
 
    qreal factor;
    SubQGraphicsScene *mScene;
    QPainter painter;
    QImage m_image;
 
    FingerPrintPainter *fpPaint;
};
#endif // SVGVIEW_H

#ifndef SVGVIEW_H
#define SVGVIEW_H

#include <QGraphicsView>
#include <QPainter>
#include "SubQGraphicsScene.h"
#include "FingerPrintPainter.h"

QT_BEGIN_NAMESPACE
class QWheelEvent;
class QPaintEvent;
class QFile;
QT_END_NAMESPACE

class SvgView : public QGraphicsView
{
    Q_OBJECT

public:
    enum RendererType { Native, OpenGL, Image };

    SvgView(QWidget *parent = 0);

    void openFile(const QFile &file);
    void setRenderer(RendererType type = Native);
    void drawBackground(QPainter *p, const QRectF &rect);

public slots:
    void setHighQualityAntialiasing(bool highQualityAntialiasing);

protected:
    void wheelEvent(QWheelEvent *event);

private:
    RendererType m_renderer;

    QGraphicsItem *m_svgItem;
    QGraphicsRectItem *m_backgroundItem;
    QGraphicsRectItem *m_outlineItem;

    qreal factor;
    SubQGraphicsScene *mScene;
    QPainter painter;
    QImage m_image;

    FingerPrintPainter *fpPaint;
};
#endif // SVGVIEW_H

To copy to clipboard, switch view to plain text mode 

subQGraphicsScene.cpp:

#include "SubQGraphicsScene.h"
#include <QWheelEvent>
#include <QMouseEvent>
#include <QGraphicsSceneMouseEvent>
#include <QGraphicsScene>
#include <iostream>
using namespace std;
SubQGraphicsScene::SubQGraphicsScene(QObject *parent)
	: QGraphicsScene(parent)
{
	// TODO Auto-generated constructor stub
}
 
SubQGraphicsScene::~SubQGraphicsScene() {
	// TODO Auto-generated destructor stub
}
 
 
void SubQGraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{
	ultimo_x = event->scenePos().x();
	ultimo_y = event->scenePos().y();
	if (event->button()  == Qt::LeftButton){
		cout << "Botón derecho en :" << ultimo_x << ", " << ultimo_y << endl;
	}else{
		cout << "Botón izquierdo en :" << ultimo_x << ", " << ultimo_y  << endl;
	}
	addEllipse(ultimo_x-10,ultimo_y-10,20,20);
}

#include "SubQGraphicsScene.h"
#include <QWheelEvent>
#include <QMouseEvent>
#include <QGraphicsSceneMouseEvent>
#include <QGraphicsScene>
#include <iostream>
using namespace std;
SubQGraphicsScene::SubQGraphicsScene(QObject *parent)
	: QGraphicsScene(parent)
{
	// TODO Auto-generated constructor stub
}

SubQGraphicsScene::~SubQGraphicsScene() {
	// TODO Auto-generated destructor stub
}


void SubQGraphicsScene::mouseReleaseEvent(QGraphicsSceneMouseEvent* event)
{
	ultimo_x = event->scenePos().x();
	ultimo_y = event->scenePos().y();
	if (event->button()  == Qt::LeftButton){
		cout << "Botón derecho en :" << ultimo_x << ", " << ultimo_y << endl;
	}else{
		cout << "Botón izquierdo en :" << ultimo_x << ", " << ultimo_y  << endl;
	}
	addEllipse(ultimo_x-10,ultimo_y-10,20,20);
}

To copy to clipboard, switch view to plain text mode 

SubQGraphicsScene.h:

#ifndef SUBQGRAPHICSSCENE_H_
#define SUBQGRAPHICSSCENE_H_
#include <QGraphicsScene>
#include <QPainter>
#include <QtGui>
 
QT_BEGIN_NAMESPACE
class QPaintEvent;
QT_END_NAMESPACE
 
class SubQGraphicsScene : public QGraphicsScene
{
	Q_OBJECT
 
public:
	SubQGraphicsScene(QObject *parent = 0);
	virtual ~SubQGraphicsScene();
 
private:
	void mouseReleaseEvent(QGraphicsSceneMouseEvent* event);
	QPainter painter;
	int ultimo_x;
	int ultimo_y;
 
};
 
#endif /* SUBQGRAPHICSSCENE_H_ */

#ifndef SUBQGRAPHICSSCENE_H_
#define SUBQGRAPHICSSCENE_H_
#include <QGraphicsScene>
#include <QPainter>
#include <QtGui>

QT_BEGIN_NAMESPACE
class QPaintEvent;
QT_END_NAMESPACE

class SubQGraphicsScene : public QGraphicsScene
{
	Q_OBJECT

public:
	SubQGraphicsScene(QObject *parent = 0);
	virtual ~SubQGraphicsScene();

private:
	void mouseReleaseEvent(QGraphicsSceneMouseEvent* event);
	QPainter painter;
	int ultimo_x;
	int ultimo_y;

};

#endif /* SUBQGRAPHICSSCENE_H_ */

To copy to clipboard, switch view to plain text mode 

SubQGraphicsItem.cpp:

#include "SubQGraphicsItem.h"
#include <QPainter>
#include <time.h>
#include <iostream>
using namespace std;
SubQGraphicsItem::SubQGraphicsItem(QRectF r) {
	// TODO Auto-generated constructor stub
	rect = r;
}
 
SubQGraphicsItem::~SubQGraphicsItem() {
	// TODO Auto-generated destructor stub
}
 
void SubQGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
{
    painter->setPen(Qt::NoPen);
    painter->setBrush(Qt::darkGray);
    srand ( time(NULL) );
    int mRandom;
    int mRandom2;
    for (int i=0; i<100; i++){
    	mRandom = rand() % 3312 + 1;
    	mRandom2 = rand() % 4416 + 1;
    	painter->drawEllipse(mRandom, mRandom2, 20, 20);
    }
}
 
QRectF SubQGraphicsItem::boundingRect() const
{
	return rect;
}

#include "SubQGraphicsItem.h"
#include <QPainter>
#include <time.h>
#include <iostream>
using namespace std;
SubQGraphicsItem::SubQGraphicsItem(QRectF r) {
	// TODO Auto-generated constructor stub
	rect = r;
}

SubQGraphicsItem::~SubQGraphicsItem() {
	// TODO Auto-generated destructor stub
}

void SubQGraphicsItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *)
{
    painter->setPen(Qt::NoPen);
    painter->setBrush(Qt::darkGray);
    srand ( time(NULL) );
    int mRandom;
    int mRandom2;
    for (int i=0; i<100; i++){
    	mRandom = rand() % 3312 + 1;
    	mRandom2 = rand() % 4416 + 1;
    	painter->drawEllipse(mRandom, mRandom2, 20, 20);
    }
}

QRectF SubQGraphicsItem::boundingRect() const
{
	return rect;
}

To copy to clipboard, switch view to plain text mode 

SubQGraphicsItem.h:

#ifndef SubQGraphicsItem_H_
#define SubQGraphicsItem_H_
#include <QGraphicsItem>
 
class SubQGraphicsItem : public QGraphicsItem
{
public:
	SubQGraphicsItem(QRectF r);
	virtual ~SubQGraphicsItem();
	QRectF boundingRect() const;
	void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
private:
	QRectF rect;
};
 
#endif /* SubQGraphicsItem_H_ */

#ifndef SubQGraphicsItem_H_
#define SubQGraphicsItem_H_
#include <QGraphicsItem>

class SubQGraphicsItem : public QGraphicsItem
{
public:
	SubQGraphicsItem(QRectF r);
	virtual ~SubQGraphicsItem();
	QRectF boundingRect() const;
	void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
private:
	QRectF rect;
};

#endif /* SubQGraphicsItem_H_ */

To copy to clipboard, switch view to plain text mode 

This code draws 30 random ellipses.

I hope it helps someone!!

Thanks!