Draw points from data file on QGraphicsView - c++

Question

As my work are going well on my long project of QT, I've tried to resolve my actual steps, but I think it is not working, so I have one question:
Draw points from data file on QGraphicsView
My code is writting actually at the end of the process a data file where the first line is the number of elements (size of the vector) and the other lines the values of the point with x and y separated by a blank.
res.dat
250
12 23
30 40
25 67
...
I would like to read this file (with the fstream) and to display each points of my vector on a QGraphicsView in order to have a graphic result, and ideally but not the most important result, to lie this point to have the desired form.
I have already tried this part of code on a main source file to test, but it is just doing a circle and I think it is not reading my file.
main.cpp
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QPointF>
#include <QVector>
#include <QApplication>
#include <fstream>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
int n;
std::ifstream ifs1("res.dat");
ifs1 >> n;
QVector <QPointF> points(n);
// Create a view, put a scene in it and add tiny circles
// in the scene
QGraphicsView * view = new QGraphicsView();
QGraphicsScene * scene = new QGraphicsScene();
view->setScene(scene);
for(int i = 1; i< n; i++)
scene->addEllipse(points[i].x(), points[i].y(), 512, 512);
// Show the view
view->show();
return a.exec();
}
Thank you in advance for reading, and for your response.

Answer 1

From your code it's completely missing the part where you read the actual coordinates of the points.
I have changed slightly your code to read the points into the vector but please remember:
a) This code is all but "solid" for example if your res.dat file is just a bit out of format it crashes.
b) With this loop you really do not need to know how many points you have in the file, right now it keeps reading until the end of file.
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
int n;
std::ifstream ifs1("res.dat");
ifs1 >> n;
QVector <QPointF> points;
qreal px,py;
while (ifs1 >> px) {
ifs1 >> py;
points.append(QPointF(px,py));
}
// Create a view, put a scene in it and add tiny circles
// in the scene
QGraphicsView * view = new QGraphicsView();
QGraphicsScene * scene = new QGraphicsScene();
view->setScene(scene);
foreach (QPointF point, points)
scene->addEllipse(point.x(), point.y(), 51, 51);
// Show the view
view->show();
return a.exec();
}

Answer 2

After you helped me, I've gone further in my code, and I have a problem I don't understand.
in the header file
//All includes
class ProjectWindow;
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
// GraphicsView 1
QGraphicsView view1;
QGraphicsScene scene1;
QGraphicsPixmapItem item1;
QGraphicsPixmapItem item2;
QString fileName;
// GraphicsView 2
QGraphicsScene scene2;
QGraphicsView view2;
QVector <QPointF> points;
qreal px,py;
QPointF point;
QPainter painter;
QGraphicsEllipseItem *ellipse;
public slots:
void openBrowser();
void drawcirc();
void drawCircle();
void runSnakes();
void displayResult();
};
#endif // MAINWINDOW_H
in the .cpp file
void MainWindow::displayResult()
{
scene2.removeItem(&item2); //removing a picture
scene2.addItem(&item2); // adding a picture
scene2.setSceneRect(scene2.itemsBoundingRect());
// Reading res.dat file and plot the contour
int m;
std::ifstream ifs2("final_contour.dat");
ifs2 >> m;
std::cout << m;
while (ifs2 >> px)
{
ifs2 >> py;
points.append(QPointF(py,px));
}
foreach(point, points)
ellipse = scene2.addEllipse(QRectF(point.y(), width-point.x(),1,1),QPen(Qt::red));
// Saving the final contour into a picture
QImage pixmap(width, width, QImage::Format_ARGB32_Premultiplied);
painter.begin(&pixmap);
painter.setRenderHint(QPainter::Antialiasing, false);
scene2.render(&painter);
painter.end();
pixmap.save("finalcontour.bmp", "BMP");
}
I want to remove the ellipse I add to the scene with removeItem() (in order to see the differents results with changing parameters), so I need to create a QGraphicsEllipseItem and to tell to the scene, addItem() that I can remove later the item with removeItem().
the header file
//All includes
class ProjectWindow;
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private:
// GraphicsView 1
QGraphicsView view1;
QGraphicsScene scene1;
QGraphicsPixmapItem item1;
QGraphicsPixmapItem item2;
QString fileName;
// GraphicsView 2
QGraphicsScene scene2;
QGraphicsView view2;
QVector <QPointF> points;
qreal px,py;
QPointF point;
QPainter painter;
QGraphicsEllipseItem ellipse; // The only line changed
public slots:
void openBrowser();
void drawcirc();
void drawCircle();
void runSnakes();
void displayResult();
};
#endif // MAINWINDOW_H
the cpp file
void MainWindow::displayResult()
{
scene2.removeItem(&item2); //removing a picture
scene2.addItem(&item2); // adding a picture
scene2.setSceneRect(scene2.itemsBoundingRect());
// Reading res.dat file and plot the contour
int m;
std::ifstream ifs2("final_contour.dat");
ifs2 >> m;
std::cout << m;
while (ifs2 >> px)
{
ifs2 >> py;
points.append(QPointF(py,px));
}
foreach(point, points)
ellipse.setRect(QRectF(point.y(), width-point.x(),1,1));
ellipse.setPen(QPen(Qt::red));
scene2.addItem(&ellipse);
// Saving the final contour into a picture
QImage pixmap(width, width, QImage::Format_ARGB32_Premultiplied);
painter.begin(&pixmap);
painter.setRenderHint(QPainter::Antialiasing, false);
scene2.render(&painter);
painter.end();
pixmap.save("finalcontour.bmp", "BMP");
}
But changing the way I want to add the ellipse, it is not displaying the whole points like this with the first way I define the ellipse:
But just one point and not the vector of points, like this: