I need help understanding QGraphicsView

[aarelovich]

Ok.

Thank you so very much. That was exactly the kind of code I was looking for. I'll try it out and get back to you.

[aarelovich]

Ok, so my dimensioning and positioning problems were solved but now I'm trying to create my own customized QGraphicsItem and I've run into a bit of a problem.

Heres is my code for my peg.h

#ifndef PEG_H
#define PEG_H
 
#include <QtGui>
#include <QtCore>
 
class Peg : public QGraphicsItem
{
public:
    Peg(QColor color);
 
    void paint( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget = 0 );
    QRectF boundingRect() const;
 
private:
    QColor color;
};
 
#endif // PEG_H

#ifndef PEG_H
#define PEG_H

#include <QtGui>
#include <QtCore>

class Peg : public QGraphicsItem
{
public:
    Peg(QColor color);

    void paint( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget = 0 );
    QRectF boundingRect() const;

private:
    QColor color;
};

#endif // PEG_H

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and its corresponding peg.cpp

#include "peg.h"
 
Peg::Peg(QColor col){
    color = col;
    setFlag(ItemIsMovable);
}
 
QRectF Peg::boundingRect() const {
    return QRectF(-1,-1,12,12);
}
 
void Peg::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget){
    painter->setPen(QPen(Qt::black));
    QRadialGradient gradient(3,3,9);
    gradient.setColorAt(0.0,Qt::white);
    gradient.setColorAt(0.5,color.lighter(120));
    gradient.setColorAt(1.0,color);
    painter->setBrush(gradient);
    painter->drawEllipse(0,0,10,10);
}

#include "peg.h"

Peg::Peg(QColor col){
    color = col;
    setFlag(ItemIsMovable);
}

QRectF Peg::boundingRect() const {
    return QRectF(-1,-1,12,12);
}

void Peg::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget){
    painter->setPen(QPen(Qt::black));
    QRadialGradient gradient(3,3,9);
    gradient.setColorAt(0.0,Qt::white);
    gradient.setColorAt(0.5,color.lighter(120));
    gradient.setColorAt(1.0,color);
    painter->setBrush(gradient);
    painter->drawEllipse(0,0,10,10);
}

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Then this is the code of the constructor of my mainwindow:

Mastermind::Mastermind(QWidget *parent)
    : QMainWindow(parent), ui(new Ui::Mastermind)
{
    ui->setupUi(this);
    scene = new QGraphicsScene(-50,-50,100,100);
    scene->setBackgroundBrush(QBrush(QColor(23,23,23)));
    ui->gvDrawArea->setScene(scene);
    ui->gvDrawArea->setRenderHints(QPainter::Antialiasing|QPainter::TextAntialiasing);
    Peg peg(Qt::red);
    scene->addItem(&peg);
}

Mastermind::Mastermind(QWidget *parent)
    : QMainWindow(parent), ui(new Ui::Mastermind)
{
    ui->setupUi(this);
    scene = new QGraphicsScene(-50,-50,100,100);
    scene->setBackgroundBrush(QBrush(QColor(23,23,23)));
    ui->gvDrawArea->setScene(scene);
    ui->gvDrawArea->setRenderHints(QPainter::Antialiasing|QPainter::TextAntialiasing);
    Peg peg(Qt::red);
    scene->addItem(&peg);
}

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The only problem is, I thought I was supposed to see a somewhat red circle somewhere on the screen yet nothing has appeared.

What did I do wrong?

Thanks for the help.

[wagmare]

use peg.setPos(x, y) to set that item in a particular location on scene ...

increase the ellipse size a little ... its very tiny on a big scene ...hahaha ..

[wagmare]

your code is completed ... see your item in the attachment ...

actually u need to inherit QObject with your custom QGraphicsItem ...
that is the problem ... now it solved ... also use setPos() in QGraphicsScene()..

class Peg : public QObject, public QGraphicsRectItem
{
 
    Q_OBJECT    //if u need any connect in future

class Peg : public QObject, public QGraphicsRectItem
{

    Q_OBJECT    //if u need any connect in future

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have a good day

[aarelovich]

Hi:

So thanks for the help. But even though I did what you told me it still did not appear. But I figured out the problem and it did not have anything to do with QGraphicsView Framework and everything to do with C++.

I chaged this code

Peg peg(Qt::red);
    scene->addItem(&peg);

Peg peg(Qt::red);
    scene->addItem(&peg);

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with this code

Peg *peg = new Peg(Qt::red);
    scene->addItem(peg);

Peg *peg = new Peg(Qt::red);
    scene->addItem(peg);

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It seems that by creating the local variable peg instead of a pointer it gets destroy at the end of the constructor therefore, it never shows up in the screen.

Thanks for all the help, I'll probably be posting more of my problems.