Pictures won't display - possible qt coordinate system confusion

[MarkoSan]

Hi to all!

With the following code I want to put some pictures on a scene:

#include "CMerchandizeSelector.h"
 
CMerchandizeSelector::CMerchandizeSelector(QWidget* pParent)
{
    QGraphicsScene* pScene=new QGraphicsScene(this);    // creates new scene
    Q_CHECK_PTR(pScene);    // checks object creation
    pScene->setItemIndexMethod(QGraphicsScene::NoIndex);
    setSceneRect(minX, minY, maxX, maxY);
    setScene(pScene);
    setWindowTitle(trUtf8("Merchandize selector"));
    // TODO: sets scene widget flags so it cannot be closed
/*
    m_pIconList=new QStringList;    // creates new string list for storing icon names
    Q_CHECK_PTR(m_pIconList);    // checks creation
*/
 
    m_cPixmap=QPixmap(100, 100);
    m_cPixmap.fill(Qt::black);
 
    QPainter p(&m_cPixmap);    // painter
    //QPainter p(this);    // painter
    p.translate(rCenterX, rCenterY);    // translated coordinate system to centre of widget
    p.setWindow(QRect(minX, minY, maxX, maxY));
    p.setViewport(QRect(minX, minY, maxX, maxY));
 
    // only for test purposes, images must be read from database
    m_cImageList.append(QImage(":/images/apple_cake.png"));
    m_cImageList.append(QImage(":/images/bigmac.png"));
    m_cImageList.append(QImage(":/images/applejuice.png"));
    m_cImageList.append(QImage(":/images/cafe_cool"));
    m_cImageList.append(QImage(":/images/chesseburger.png"));
    m_cImageList.append(QImage(":/images/coke.png"));
 
    // computes positions for images
    for (m_iCounter=0; m_iCounter<iLoadTreshold; m_iCounter++)
    {
        QPointF tmpPoint=computePoint(0, 0, rCircleRadius, m_iCounter*rAngle*Pi/180);
        m_cImagePointList.append(tmpPoint);
        qDebug() << "(" << tmpPoint.rx() << ", " << tmpPoint.ry() << "); ";
    }
 
    // draws an image at computed coords
    for (m_iCounter=0; m_iCounter<m_cImageList.count(); m_iCounter++)
    {
        p.drawImage(m_cImagePointList.at(m_iCounter), m_cImageList.at(m_iCounter));
        //p.drawImage(QPointF(80*m_iCounter, 0), m_cImageList.at(m_iCounter));
    }
}
 
CMerchandizeSelector::~CMerchandizeSelector()
{
}
 
// computes cartesian coordinates for given circle and its angle
QPointF CMerchandizeSelector::computePoint(qreal rOriginX, qreal rOriginY, qreal rRadius, qreal rAngle)
{
    QPointF p;    // point
    p.setX(rOriginX+rRadius*cos(rAngle*Pi/180));    // computes x
    p.setY(rOriginX+rRadius*sin(rAngle*Pi/180));    // computes y
    //p.setX(rOriginX+rRadius*cos(rAngle));    // computes x
    //p.setY(rOriginX+rRadius*sin(rAngle));    // computes y
    return p;    // returns p
}
 
// painter event
/*
void CMerchandizeSelector::paintEvent(QPaintEvent *e)
{
    QPainter p(this);
    p.setClipRect(e->rect());
    p.drawTiledPixmap(rect(), m_cPixmap);
    
    for (m_iCounter=0; m_iCounter<m_cImageList.count(); m_iCounter++)
    {
        //p.drawImage(m_cImagePointList.at(m_iCounter), m_cImageList.at(m_iCounter));
        p.drawImage(QPointF(80*m_iCounter, 0), m_cImageList.at(m_iCounter));
    }
}
*/

#include "CMerchandizeSelector.h"

CMerchandizeSelector::CMerchandizeSelector(QWidget* pParent)
{
    QGraphicsScene* pScene=new QGraphicsScene(this);    // creates new scene
    Q_CHECK_PTR(pScene);    // checks object creation
    pScene->setItemIndexMethod(QGraphicsScene::NoIndex);
    setSceneRect(minX, minY, maxX, maxY);
    setScene(pScene);
    setWindowTitle(trUtf8("Merchandize selector"));
    // TODO: sets scene widget flags so it cannot be closed
/*
    m_pIconList=new QStringList;    // creates new string list for storing icon names
    Q_CHECK_PTR(m_pIconList);    // checks creation
*/
    
    m_cPixmap=QPixmap(100, 100);
    m_cPixmap.fill(Qt::black);

    QPainter p(&m_cPixmap);    // painter
    //QPainter p(this);    // painter
    p.translate(rCenterX, rCenterY);    // translated coordinate system to centre of widget
    p.setWindow(QRect(minX, minY, maxX, maxY));
    p.setViewport(QRect(minX, minY, maxX, maxY));

    // only for test purposes, images must be read from database
    m_cImageList.append(QImage(":/images/apple_cake.png"));
    m_cImageList.append(QImage(":/images/bigmac.png"));
    m_cImageList.append(QImage(":/images/applejuice.png"));
    m_cImageList.append(QImage(":/images/cafe_cool"));
    m_cImageList.append(QImage(":/images/chesseburger.png"));
    m_cImageList.append(QImage(":/images/coke.png"));
    
    // computes positions for images
    for (m_iCounter=0; m_iCounter<iLoadTreshold; m_iCounter++)
    {
        QPointF tmpPoint=computePoint(0, 0, rCircleRadius, m_iCounter*rAngle*Pi/180);
        m_cImagePointList.append(tmpPoint);
        qDebug() << "(" << tmpPoint.rx() << ", " << tmpPoint.ry() << "); ";
    }
    
    // draws an image at computed coords
    for (m_iCounter=0; m_iCounter<m_cImageList.count(); m_iCounter++)
    {
        p.drawImage(m_cImagePointList.at(m_iCounter), m_cImageList.at(m_iCounter));
        //p.drawImage(QPointF(80*m_iCounter, 0), m_cImageList.at(m_iCounter));
    }
}

CMerchandizeSelector::~CMerchandizeSelector()
{
}

// computes cartesian coordinates for given circle and its angle
QPointF CMerchandizeSelector::computePoint(qreal rOriginX, qreal rOriginY, qreal rRadius, qreal rAngle)
{
    QPointF p;    // point
    p.setX(rOriginX+rRadius*cos(rAngle*Pi/180));    // computes x
    p.setY(rOriginX+rRadius*sin(rAngle*Pi/180));    // computes y
    //p.setX(rOriginX+rRadius*cos(rAngle));    // computes x
    //p.setY(rOriginX+rRadius*sin(rAngle));    // computes y
    return p;    // returns p
}

// painter event
/*
void CMerchandizeSelector::paintEvent(QPaintEvent *e)
{
    QPainter p(this);
    p.setClipRect(e->rect());
    p.drawTiledPixmap(rect(), m_cPixmap);
    
    for (m_iCounter=0; m_iCounter<m_cImageList.count(); m_iCounter++)
    {
        //p.drawImage(m_cImagePointList.at(m_iCounter), m_cImageList.at(m_iCounter));
        p.drawImage(QPointF(80*m_iCounter, 0), m_cImageList.at(m_iCounter));
    }
}
*/

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Here is header file:

#ifndef CMERCHANDIZESELECTOR_H_
#define CMERCHANDIZESELECTOR_H_
 
// qt includes
#include <QtGui/QGraphicsView>
//#include <QtGui/QGraphicsScene>
//#include <QtGui/QGraphicsItem>
#include <QtGui/QImage>
//#include <QtCore/QPointer>
//#include <QtCore/QStringList>
#include <QtCore/QPointF>
#include <QtCore/QRect>
//#include <QtCore/QRectF>
#include <QtGui/QPainter>
#include <QtGui/QPixmap>
#include <QtGui/QPaintEvent>
#include <QtDebug>
 
// math support includes
#include <cmath>
 
// custom includes
#include "globals.h"
 
class CMerchandizeSelector : public QGraphicsView
{
    Q_OBJECT
 
public:
    CMerchandizeSelector(QWidget* pParent=0);
    virtual ~CMerchandizeSelector();
 
private:
    QList<QImage> m_cImageList;    // list of icon filenames on 3d graphics browse
    QList<QPointF> m_cImagePointList;    // list of coordinates for icons
    quint16 m_iCounter;    // protected loop counter
    QPixmap m_cPixmap;    // pixmap
    //QPointer <CLens> m_pLens;    // lens for zoming selected merchandize
    //QStringList m_pIconList;    // list of icon filenames on 3d graphics browse
/*
    void keyPressEvent(QKeyEvent *event);
    void timerEvent(QTimerEvent *event);
    void wheelEvent(QWheelEvent *event);
    void drawBackground(QPainter *painter, const QRectF &rect);
*/
    //void paintEvent(QPaintEvent *e);    // painter event
    QPointF computePoint(qreal rOriginX, qreal rOriginY, qreal rRadius, qreal rAngle);
};
 
#endif /*CMERCHANDIZESELECTOR_H_*/

#ifndef CMERCHANDIZESELECTOR_H_
#define CMERCHANDIZESELECTOR_H_

// qt includes
#include <QtGui/QGraphicsView>
//#include <QtGui/QGraphicsScene>
//#include <QtGui/QGraphicsItem>
#include <QtGui/QImage>
//#include <QtCore/QPointer>
//#include <QtCore/QStringList>
#include <QtCore/QPointF>
#include <QtCore/QRect>
//#include <QtCore/QRectF>
#include <QtGui/QPainter>
#include <QtGui/QPixmap>
#include <QtGui/QPaintEvent>
#include <QtDebug>

// math support includes
#include <cmath>

// custom includes
#include "globals.h"

class CMerchandizeSelector : public QGraphicsView
{
    Q_OBJECT

public:
    CMerchandizeSelector(QWidget* pParent=0);
    virtual ~CMerchandizeSelector();

private:
    QList<QImage> m_cImageList;    // list of icon filenames on 3d graphics browse
    QList<QPointF> m_cImagePointList;    // list of coordinates for icons
    quint16 m_iCounter;    // protected loop counter
    QPixmap m_cPixmap;    // pixmap
    //QPointer <CLens> m_pLens;    // lens for zoming selected merchandize
    //QStringList m_pIconList;    // list of icon filenames on 3d graphics browse
/*
    void keyPressEvent(QKeyEvent *event);
    void timerEvent(QTimerEvent *event);
    void wheelEvent(QWheelEvent *event);
    void drawBackground(QPainter *painter, const QRectF &rect);
*/
    //void paintEvent(QPaintEvent *e);    // painter event
    QPointF computePoint(qreal rOriginX, qreal rOriginY, qreal rRadius, qreal rAngle);
};

#endif /*CMERCHANDIZESELECTOR_H_*/

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And here are constants, used in app (file globals.h):

// globals.h
 
#ifndef GLOBALS_H
#define GLOBALS_H
 
// qt includes
#include <QtGlobal>
 
// scene rect coords
static const qint16 minX=0;
static const qint16 minY=0;
static const qint16 maxX=600;    // scene width
static const qint16 maxY=600;    // scene height
 
//static const qreal rCenterX=(maxX+minX)/2;    // scente centre x
static const qreal rCenterX=(maxX-minX)/2;    // scente centre x
//static const qreal rCenterY=(maxY+minY)/2;    // scente centre x
static const qreal rCenterY=(maxY-minY)/2;    // scente centre x
static const qreal rCirleMargin=20.0;    // circle margin
static const qreal rCircleRadius=maxX-rCenterX-rCirleMargin;    // radius of circle
 
// geometric constants
static const qreal pi=3.14159265358979323846264338327950288419716939937510;    // pi constant
static const qreal Pi=pi;    // alias for pi
static const quint8 iLoadTreshold=10;    // icon load treshold
static const qreal rEmtpyCircle=0;    // emtpy circle
static const qreal rFullCircle=360;    // full circle has 360 degrees
static const qreal rAngle=rFullCircle/iLoadTreshold;    // merchandize icon appears every rAngle degrees on rotary
                                                        // merchandize selector
 
#endif

// globals.h

#ifndef GLOBALS_H
#define GLOBALS_H

// qt includes
#include <QtGlobal>

// scene rect coords
static const qint16 minX=0;
static const qint16 minY=0;
static const qint16 maxX=600;    // scene width
static const qint16 maxY=600;    // scene height

//static const qreal rCenterX=(maxX+minX)/2;    // scente centre x
static const qreal rCenterX=(maxX-minX)/2;    // scente centre x
//static const qreal rCenterY=(maxY+minY)/2;    // scente centre x
static const qreal rCenterY=(maxY-minY)/2;    // scente centre x
static const qreal rCirleMargin=20.0;    // circle margin
static const qreal rCircleRadius=maxX-rCenterX-rCirleMargin;    // radius of circle

// geometric constants
static const qreal pi=3.14159265358979323846264338327950288419716939937510;    // pi constant
static const qreal Pi=pi;    // alias for pi
static const quint8 iLoadTreshold=10;    // icon load treshold
static const qreal rEmtpyCircle=0;    // emtpy circle
static const qreal rFullCircle=360;    // full circle has 360 degrees
static const qreal rAngle=rFullCircle/iLoadTreshold;    // merchandize icon appears every rAngle degrees on rotary
                                                        // merchandize selector

#endif

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Can anyone help me please why pictures are not shown?! I read the docs about qt's coordinate system, but I simply do not get it how it works!!!!

Please help!

[jpn]

Try using QGraphicsPixmapItems instead of trying to paint images by hand.

[MarkoSan]

QGraphicsPixmap items? I tried, picture is shown, but I cannot move it to arbitrary coordinate.

[jpn]

QGraphicsPixmap items? I tried, picture is shown, but I cannot move it to arbitrary coordinate.

You can move them like any other items; QGraphicsItem::setPos().

[MarkoSan]

But what is the difference between my current approach and qpixmapitem approach?

[jpn]

But what is the difference between my current approach and qpixmapitem approach?

What's the point using a QGraphicsScene/QGraphicsView without items? QGraphicsView has a sophisticated paintEvent() will its caching facilities and such. There are specialized QGraphicsView::draw*() and QGraphicsItem::paint() methods in case you want to draw anything by hand. I wouldn't suggest reimplementing QGraphicsView::paintEvent(), it will just destroy the fine framework.

[MarkoSan]

How do I add QImage to QGraphicsScene? I am reading docs and I just do not get it ...

[jpn]

How do I add QImage to QGraphicsScene? I am reading docs and I just do not get it ...

Again, use QGraphicsPixmapItems. I thought you said you already got one visible. You may use QPixmap::fromImage() to convert a QImage to QPixmap.

[MarkoSan]

I tried to used it before, something did not work. I gor some errors about QGraphicsPixelItem contructor that is private or sometinhg lke that.

[jpn]

I tried to used it before, something did not work. I gor some errors about QGraphicsPixelItem contructor that is private or sometinhg lke that.

The copy constructor of QGraphicsPixmapItem is private which means that you cannot copy QGraphicsPixmapItems.

The easiest way is to use the convenience method of QGraphicsScene:

QGraphicsPixmapItem* item = scene->addPixmap(pixmap);
item->setPos(...);

QGraphicsPixmapItem* item = scene->addPixmap(pixmap);
item->setPos(...);

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but you can create QGraphicsPixmapItems yourself as well:

QGraphicsPixmapItem* item = new QGraphicsPixmapItem(pixmap, parent);
scene->addItem(item);
item->setPos(...);

QGraphicsPixmapItem* item = new QGraphicsPixmapItem(pixmap, parent);
scene->addItem(item);
item->setPos(...);

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[MarkoSan]

The copy constructor of QGraphicsPixmapItem is private which means that you cannot copy QGraphicsPixmapItems.

The easiest way is to use the convenience method of QGraphicsScene:

QGraphicsPixmapItem* item = scene->addPixmap(pixmap);
item->setPos(...);

QGraphicsPixmapItem* item = scene->addPixmap(pixmap);
item->setPos(...);

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but you can create QGraphicsPixmapItems yourself as well:

QGraphicsPixmapItem* item = new QGraphicsPixmapItem(pixmap, parent);
scene->addItem(item);
item->setPos(...);

QGraphicsPixmapItem* item = new QGraphicsPixmapItem(pixmap, parent);
scene->addItem(item);
item->setPos(...);

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And one more question: why is the copy contructor of QGraphicsPixmapItem private, I mean, what do we gain with that?

Thank you very very much for help, let me now dig into it and i will report results.