Qpainter

**rafik** · 28th January 2016, 14:00

Hello,

i want to draw some points (gravity centers) in a QImage, how i can do that ? i heared about QPainter but i don't understand how doing that?

here the code i want to show the points in the fensec object

Qt Code:

Switch view

#include "otsu.h"
#include "fenetreprincipale.h"
 
FenetrePrincipale::FenetrePrincipale(): QMainWindow()
{
 
    label =new QLabel(&fentroi);
 
    label->setGeometry(100,100,400,400);
    QMenu *menuFichier = menuBar()->addMenu("Fichier");
    QAction *actionOuvrir = new QAction("Ouvrir", this);
    QAction *actionQuitter = new QAction("Quitter", this);
    menuFichier->addAction(actionOuvrir);
    menuFichier->addAction(actionQuitter);
 
    QMenu *menuTraitement = menuBar()->addMenu("Traitement");
    QAction *actionBinarisation = new QAction("Binarisation", this);
    menuTraitement->addAction(actionBinarisation);
 
    QObject::connect(actionOuvrir, SIGNAL(triggered(bool)), this, SLOT(ouvrir()));
    QObject::connect(actionQuitter, SIGNAL(triggered(bool)), this, SLOT(close()));
 
    QObject::connect(actionBinarisation, SIGNAL(triggered(bool)), this, SLOT(traiterOtsu()));
}
void FenetrePrincipale::ouvrir()
{
   nomFichier = QFileDialog::getOpenFileName(this, tr("Open File"),"C:/Users/amine/Downloads");
 
 
 
   image = new QImage(nomFichier);
   QPixmap pixmap;
   pixmap.convertFromImage(*image);
   label->setPixmap(pixmap);
   fentroi.show(); // fentroi (fenetre qui affiche l'image) attribut de fenetre principale
   label->update();
 
}
 
void FenetrePrincipale::traiterOtsu()
{
    OtsuAlgo traitement(nomFichier);
    traitement.traiter(nomFichier);
    traitement.binarisation();
    QImage *im = new QImage(traitement.getImage());
    QLabel *label1 = new QLabel(&fenSec);
    label1->setGeometry(100,100, 400, 400);
    label1->setPixmap(QPixmap::fromImage(*im));
    QLCDNumber *lcd = new QLCDNumber(&fenSec);
    lcd->move(70,70);
    lcd->setSegmentStyle(QLCDNumber::Flat);
    lcd->display(traitement.getSeuil());
    fenSec.show();
    traitement.detection();
}

#include "otsu.h"
#include "fenetreprincipale.h"

FenetrePrincipale::FenetrePrincipale(): QMainWindow()
{

    label =new QLabel(&fentroi);

    label->setGeometry(100,100,400,400);
    QMenu *menuFichier = menuBar()->addMenu("Fichier");
    QAction *actionOuvrir = new QAction("Ouvrir", this);
    QAction *actionQuitter = new QAction("Quitter", this);
    menuFichier->addAction(actionOuvrir);
    menuFichier->addAction(actionQuitter);

    QMenu *menuTraitement = menuBar()->addMenu("Traitement");
    QAction *actionBinarisation = new QAction("Binarisation", this);
    menuTraitement->addAction(actionBinarisation);

    QObject::connect(actionOuvrir, SIGNAL(triggered(bool)), this, SLOT(ouvrir()));
    QObject::connect(actionQuitter, SIGNAL(triggered(bool)), this, SLOT(close()));

    QObject::connect(actionBinarisation, SIGNAL(triggered(bool)), this, SLOT(traiterOtsu()));
}
void FenetrePrincipale::ouvrir()
{
   nomFichier = QFileDialog::getOpenFileName(this, tr("Open File"),"C:/Users/amine/Downloads");



   image = new QImage(nomFichier);
   QPixmap pixmap;
   pixmap.convertFromImage(*image);
   label->setPixmap(pixmap);
   fentroi.show(); // fentroi (fenetre qui affiche l'image) attribut de fenetre principale
   label->update();

}

void FenetrePrincipale::traiterOtsu()
{
    OtsuAlgo traitement(nomFichier);
    traitement.traiter(nomFichier);
    traitement.binarisation();
    QImage *im = new QImage(traitement.getImage());
    QLabel *label1 = new QLabel(&fenSec);
    label1->setGeometry(100,100, 400, 400);
    label1->setPixmap(QPixmap::fromImage(*im));
    QLCDNumber *lcd = new QLCDNumber(&fenSec);
    lcd->move(70,70);
    lcd->setSegmentStyle(QLCDNumber::Flat);
    lcd->display(traitement.getSeuil());
    fenSec.show();
    traitement.detection();
}

To copy to clipboard, switch view to plain text mode

if some one can help me
thank you.

**anda_skoa** · 28th January 2016, 14:08

Don't create QImage on the heap, you will just more easily leak it.

QImage is derived from QPaintDevice, which is what QPainter works on.

Just create a QPainter instance, call its begin() method with the image as its argument, paint using the painters methods and then call end().
The image then contains whatever you have drawn.

Cheers,
_

**rafik** · 28th January 2016, 14:59

thank you, i will try it later , i have a problem with my program

**rafik** · 28th January 2016, 19:43

i tried this (i added the last lines in cpp) but i didn't have the points, i think i didn't understand
fenetrePrincipale.h

Qt Code:

Switch view

#ifndef FENETREPRINCIPALE_H
#define FENETREPRINCIPALE_H
 
#include <QtWidgets>
 
class FenetrePrincipale : public QMainWindow
{
    Q_OBJECT
public :
    FenetrePrincipale();
public slots :
    void ouvrir();
    void traiterOtsu();
private:
    QImage *image;
    QLabel *label;
    QString nomFichier;
    QWidget fentroi;
    QWidget fenSec;
 
 
 
};
 
#endif // FENETREPRINCIPALE_H

#ifndef FENETREPRINCIPALE_H
#define FENETREPRINCIPALE_H

#include <QtWidgets>

class FenetrePrincipale : public QMainWindow
{
    Q_OBJECT
public :
    FenetrePrincipale();
public slots :
    void ouvrir();
    void traiterOtsu();
private:
    QImage *image;
    QLabel *label;
    QString nomFichier;
    QWidget fentroi;
    QWidget fenSec;



};

#endif // FENETREPRINCIPALE_H

To copy to clipboard, switch view to plain text mode

fenetrePrincipale.cpp

Qt Code:

Switch view

#include "otsu.h"
#include "fenetreprincipale.h"
 
FenetrePrincipale::FenetrePrincipale(): QMainWindow()
{
 
    label =new QLabel(&fentroi);
 
    label->setGeometry(100,100,400,400);
    QMenu *menuFichier = menuBar()->addMenu("Fichier");
    QAction *actionOuvrir = new QAction("Ouvrir", this);
    QAction *actionQuitter = new QAction("Quitter", this);
    menuFichier->addAction(actionOuvrir);
    menuFichier->addAction(actionQuitter);
 
    QMenu *menuTraitement = menuBar()->addMenu("Traitement");
    QAction *actionBinarisation = new QAction("Binarisation", this);
    menuTraitement->addAction(actionBinarisation);
 
    QObject::connect(actionOuvrir, SIGNAL(triggered(bool)), this, SLOT(ouvrir()));
    QObject::connect(actionQuitter, SIGNAL(triggered(bool)), this, SLOT(close()));
 
    QObject::connect(actionBinarisation, SIGNAL(triggered(bool)), this, SLOT(traiterOtsu()));
}
void FenetrePrincipale::ouvrir()
{
   nomFichier = QFileDialog::getOpenFileName(this, tr("Open File"),"C:/Users/amine/Downloads");
 
 
 
   image = new QImage(nomFichier);
   QPixmap pixmap;
   pixmap.convertFromImage(*image);
   label->setPixmap(pixmap);
   fentroi.show(); // fentroi (fenetre qui affiche l'image) attribut de fenetre principale
   label->update();
 
}
 
void FenetrePrincipale::traiterOtsu()
{
    QVector<Position> v;
    OtsuAlgo traitement(nomFichier);
    traitement.traiter(nomFichier);
    traitement.binarisation();
    QImage *im = new QImage(traitement.getImage());
    QLabel *label1 = new QLabel(&fenSec);
    label1->setGeometry(100,100, 400, 400);
    label1->setPixmap(QPixmap::fromImage(*im));
    QLCDNumber *lcd = new QLCDNumber(&fenSec);
    lcd->move(70,70);
    lcd->setSegmentStyle(QLCDNumber::Flat);
    lcd->display(traitement.getSeuil());
    fenSec.show();
    traitement.detection();
    traitement.centrer();
 
    v = traitement.getCentres();
 
    QFile monFichier("C:/Users/amine/Downloads/essai.txt");
        if (!monFichier.open(QIODevice::WriteOnly|QIODevice::Text))
            return;
        QTextStream flux(&monFichier);
        for(int i=0;i< v.size();i++)
        {
            flux << "i " <<  v[i].getI() << " " << "j " << v[i].getJ() << endl;
        }
 
    for (int i=0;i<v.size();i++)
    {
        QPainter painter;
        QPen pen(Qt::blue);
        painter.setPen(pen);
        painter.begin(image);
        painter.drawPoint(v[i].getI(),v[i].getJ());
        painter.end();
    }
 
}

#include "otsu.h"
#include "fenetreprincipale.h"

FenetrePrincipale::FenetrePrincipale(): QMainWindow()
{

    label =new QLabel(&fentroi);

    label->setGeometry(100,100,400,400);
    QMenu *menuFichier = menuBar()->addMenu("Fichier");
    QAction *actionOuvrir = new QAction("Ouvrir", this);
    QAction *actionQuitter = new QAction("Quitter", this);
    menuFichier->addAction(actionOuvrir);
    menuFichier->addAction(actionQuitter);

    QMenu *menuTraitement = menuBar()->addMenu("Traitement");
    QAction *actionBinarisation = new QAction("Binarisation", this);
    menuTraitement->addAction(actionBinarisation);

    QObject::connect(actionOuvrir, SIGNAL(triggered(bool)), this, SLOT(ouvrir()));
    QObject::connect(actionQuitter, SIGNAL(triggered(bool)), this, SLOT(close()));

    QObject::connect(actionBinarisation, SIGNAL(triggered(bool)), this, SLOT(traiterOtsu()));
}
void FenetrePrincipale::ouvrir()
{
   nomFichier = QFileDialog::getOpenFileName(this, tr("Open File"),"C:/Users/amine/Downloads");



   image = new QImage(nomFichier);
   QPixmap pixmap;
   pixmap.convertFromImage(*image);
   label->setPixmap(pixmap);
   fentroi.show(); // fentroi (fenetre qui affiche l'image) attribut de fenetre principale
   label->update();

}

void FenetrePrincipale::traiterOtsu()
{
    QVector<Position> v;
    OtsuAlgo traitement(nomFichier);
    traitement.traiter(nomFichier);
    traitement.binarisation();
    QImage *im = new QImage(traitement.getImage());
    QLabel *label1 = new QLabel(&fenSec);
    label1->setGeometry(100,100, 400, 400);
    label1->setPixmap(QPixmap::fromImage(*im));
    QLCDNumber *lcd = new QLCDNumber(&fenSec);
    lcd->move(70,70);
    lcd->setSegmentStyle(QLCDNumber::Flat);
    lcd->display(traitement.getSeuil());
    fenSec.show();
    traitement.detection();
    traitement.centrer();

    v = traitement.getCentres();

    QFile monFichier("C:/Users/amine/Downloads/essai.txt");
        if (!monFichier.open(QIODevice::WriteOnly|QIODevice::Text))
            return;
        QTextStream flux(&monFichier);
        for(int i=0;i< v.size();i++)
        {
            flux << "i " <<  v[i].getI() << " " << "j " << v[i].getJ() << endl;
        }

    for (int i=0;i<v.size();i++)
    {
        QPainter painter;
        QPen pen(Qt::blue);
        painter.setPen(pen);
        painter.begin(image);
        painter.drawPoint(v[i].getI(),v[i].getJ());
        painter.end();
    }

}

To copy to clipboard, switch view to plain text mode

**anda_skoa** · 28th January 2016, 19:49

setPen after begin

Also how did you determine that it doesn't work?
You are neither saving nor displaying the modified image.

Cheers,
_

**rafik** · 28th January 2016, 20:46

i am a bad programmer,
thank you Mr anda, it run now

just a question, can i resize the QLabel to appear larger?

**anda_skoa** · 28th January 2016, 21:04

Of course, see QWidget::resize( or QWidget::setGeometry().

Cheers,
_

**rafik** · 28th January 2016, 21:09

thank you Mr anda.

Thread: Qpainter

Thread Tools

Search Thread

Display

Qpainter

Re: Qpainter

Re: Qpainter

Re: Qpainter

Re: Qpainter

The following user says thank you to anda_skoa for this useful post:

Re: Qpainter

Re: Qpainter

The following user says thank you to anda_skoa for this useful post:

Re: Qpainter

Similar Threads

Using Text/Fonts with QPainter in combination with QPainter::scale()

QPainter(&QPrinter) & QPainter(&QImage) communication

QPainter::Antialiasing | QPainter::SmoothPixmapTransform bug on Linux?

QPainter::save and QPAinter::restore()

Why QPainter::rotate doesn't affect QPainter::boundingRect?

Bookmarks

Bookmarks

Posting Permissions