How to draw a Rectangle in Qgraphicsview dynamically (runtime), using Qt4

Dayama Pradeep

I'm just a starter on QT platform and trying to draw a Rectangle Dynamically. The program uses 3 Mouse events namely

mousePressEvent
mouseMoveEvent
mouseReleaseEvent
Problems is All mouse Events are called but the rectangle is not drawn.

Here is the code snippet

main.cpp

#include <QtGui/QApplication>
#include "dialog.h"

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

dialog.cpp

#include "dialog.h"
#include "ui_dialog.h"
#include "mysquare.h"

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);
    setMouseTracking(true);
    scene = new QGraphicsScene(this);
    ui->graphicsView->setScene(scene);
    scene->setBackgroundBrush(Qt::black);
    square = new mySquare;
    scene->addItem(square);
    square->mPix = QPixmap(400,400);
    square->mPix.fill(Qt::white);
    //scene->addPixmap(mPix);
    scene->addPixmap(square->mPix);


}

Dialog::~Dialog()
{
    delete ui;
}

void Dialog::on_pushButton_clicked()
{
   square->selectedTool = 1;
}

dialog.h

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>
#include <QtCore>
#include <QtGui>
#include "mysquare.h"

namespace Ui {
class Dialog;
}

class Dialog : public QDialog
{
    Q_OBJECT
    
public:
    explicit Dialog(QWidget *parent = 0);
    ~Dialog();
    
private slots:
    void on_pushButton_clicked();

private:
    Ui::Dialog *ui;
    QGraphicsScene *scene;
    mySquare *square;

};

#endif // DIALOG_H

mysquare.cpp

#include "mysquare.h"

using namespace std;


mySquare::mySquare()
{
    pressed  = false;
    //setFlag(ItemIsMovable);
    selectedTool = 1;
    mPix = QPixmap(400,400);
    mPix.fill(Qt::white);
}

QRectF mySquare::boundingRect() const
{
    return QRectF(0,0,200,200);
}



void mySquare::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    //painter->begin(this);
    QPen pen(Qt::red);
    painter->setPen(pen);
    //painter->setPen(Qt::blue);
    //QRectF rec = boundingRect();
    if(pressed)
    {
       // painter->drawPixmap();
        painter->drawPixmap(0,0,mPix);

        painter->drawRect(mRect);
        drawStarted = true;
    }
    else if (drawStarted)
    {
        QPainter tempPainter(&mPix);
        tempPainter.drawRect(mRect);
        painter->drawPixmap(0,0,mPix);
    }

    //painter->end();
//    QRectF rec = boundingRect();
//    QBrush brush(Qt::blue);

//    if(pressed)
//    {
//        brush.setColor(Qt::red);
//    }
//    else
//    {
//        brush.setColor(Qt::black);
//    }
//    painter->fillRect(rec,brush);
//    painter->drawRect(rec);
}

void mySquare::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    pressed = true;

    y = event->pos();
    cout<<"Pos X : "<<y.x() <<endl;
    cout<<"Pos Y : "<<y.y() <<endl;

    if(selectedTool == 1)
    {
        mRect.setTopLeft(event->pos());
        mRect.setBottomRight(event->pos());

        X_1 = mRect.x();
        //X_1 = 400 - X_1;
        Y_1 = mRect.y();
        //Y_1 = 600 - Y_1;
        Y_2 = Y_1;
        X_3 = X_1;
        cout << "Value of x_start axis " << X_1 <<endl;
        cout << "Value of y_start axis " << Y_1 <<endl;
    }
    else if (selectedTool == 2)
    {

    }
    update();
    //cout<<"Inside mousePressEvent\n";
    //QGraphicsItem::mousePressEvent(event);
}

void mySquare::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    cout<<"Inside mouseMoveEvent \n";
    if(event->type() == QEvent::MouseMove)
    {
        if(selectedTool == 1){
            mRect.setBottomRight(event->pos());
        }
        else if (selectedTool == 2){
            //mLine.setP2(event->pos());
        }
    }
    update();
}

void mySquare::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
//    X_4 = event->x();
//    X_4 = 400 - X_4;
//    Y_4 = event->y();
//    Y_4 = 600 - Y_4;
//    Y_3 = Y_4;
//    X_2 = X_4;
//    cout << "Value of x_end axis " << event->x() <<endl;
//    cout << "Value of y_end axis " << event->y() <<endl;

//    cout << "Value of all mapped coordinates \n" << "X_1 = " << X_1 << "\t\t Y_1 = " << Y_1 << "\n X_2 = " << X_2 << "\t Y_2 = " << Y_2 << "\n X_3 = " << X_3 << "\t Y_3 = " << Y_3 << "\n X_4 = " << X_4 << "\t Y_4 = "  << Y_4 <<endl;

    pressed = false;
    update();
    cout<<"Inside mouseReleaseEvent \n";
    //QGraphicsItem::mouseReleaseEvent(event);
}

mysquare.h

#ifndef MYSQUARE_H
#define MYSQUARE_H
#include <QPainter>
#include <QGraphicsItem>
#include <QDebug>
#include <QPainter>
#include <iostream>
#include <QPixmap>
#include <QPaintEvent>
#include <QGraphicsSceneMouseEvent>

class mySquare: public QGraphicsItem
{
public:
    mySquare();
    int selectedTool;
    QPixmap mPix;
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
   //void paintEvent(QPaintEvent *event);
    bool pressed;
    bool drawStarted;
    int X_1, Y_1,X_2, Y_2,X_3, Y_3,X_4, Y_4;

protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event);
    void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);

private:
    QRectF mRect;
    QPointF y;


private slots:

};

#endif // MYSQUARE_H

Please guide me,
Thanks

mrjj

hi and welcome
You seem to have disabled your paintEvent??
You shall paint ONLY in the paintEvent.
U can call your paint function but do it from PaintEvent.

also , this might be usefull
http://www.walletfox.com/course/qgraphicsitemruntimedrawing.php

Dayama Pradeep

@mrjj thanks a lot. will go through the link you shared.

Dayama Pradeep

@mrjj the code shown above uses QGraphicsItem. QGraphicsItem has paint as given in this doccument see here. paintEvent is in Qwidget, as per this link.
How do i Enable paintEvent in QGraphicsItem:?

mrjj

@Dayama-Pradeep said:

QGraphicsItem

Hi sorry
You did right.
For QGraphicsItem docs says
"The paint() function is called by QGraphicsView "
So no paintEvent involved. ( i thought it was a widget)

So you should insert some qDebug << "func: 1" ;
around in code and see if your paint is called.