QDialog does not appear until calculations are finished

[Richard H]

Hi, I have a problem with the GUI for a laser beam propagation simulation I am currently writing with C++ and QT. The simulation itself works, but I implemented a dialog which should actually update a plot, using QCustomPlot and a progressBar. Unfortunately, the QDialog only appears after all the calculations are done, showing the plot of the final result and a progress bar at 100%.

Is there any way to make sure my dialog is actually visible during the calculations?

Here is how I create the dialog, after the preceding information has been processed:

void bpmSettings::runBPM()
{
    //...
    bpmdialog *b = new bpmdialog;
    b->show();
    this->close();
}

void bpmSettings::runBPM()
{
    //...
    bpmdialog *b = new bpmdialog;
    b->show();
    this->close();
}

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Here is the header of the dialog:

#ifndef BPMDIALOG_H
#define BPMDIALOG_H
 
#include <QDialog>
#include "vector2d.h" // a vector class I wrote which the simulation is based on
 
extern GaussData globalData;
 
namespace Ui {
class bpmdialog;
}
 
class bpmdialog : public QDialog
{
    Q_OBJECT
 
public:
    explicit bpmdialog(QWidget *parent = 0);
    ~bpmdialog();
 
private:
    Ui::bpmdialog *ui;
    void envPlot(const vector2d<double>& field); // plots the vector2d field by using the QCustomPlot widget in the ui.
    void bpm(); // starts simulation
};
 
#endif // BPMDIALOG_H

#ifndef BPMDIALOG_H
#define BPMDIALOG_H

#include <QDialog>
#include "vector2d.h" // a vector class I wrote which the simulation is based on

extern GaussData globalData;

namespace Ui {
class bpmdialog;
}

class bpmdialog : public QDialog
{
    Q_OBJECT

public:
    explicit bpmdialog(QWidget *parent = 0);
    ~bpmdialog();

private:
    Ui::bpmdialog *ui;
    void envPlot(const vector2d<double>& field); // plots the vector2d field by using the QCustomPlot widget in the ui.
    void bpm(); // starts simulation
};

#endif // BPMDIALOG_H

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And this is how my implementation of the dialog looks like:

bpmdialog::bpmdialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::bpmdialog)
{
    ui->setupUi(this);
    bpm();
}

bpmdialog::bpmdialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::bpmdialog)
{
    ui->setupUi(this);
    bpm();
}

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I hope I provided enough information. The bpm() method is basically a for loop calculating a new 2d field in every iteration, by using a Gauss Seidel algorithm to solve a linear system. The 2d field is then plotted with the envPlot(field) method in every iteration.

Thank you very much in advance for your help!
Best regards,
Richard