Qpainter

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

Code:

---

#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();
}

---

if some one can help me
thank you.

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,
_

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

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

Code:

---

#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

---

fenetrePrincipale.cpp

Code:

---

#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();
    }
 
}

---

setPen after begin

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

Cheers,
_

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

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

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

Cheers,
_

thank you Mr anda.