Simple QImage animations in Qt

Question

I would like to achieve the following in a simple (not necessarily most efficient and/or elegant way): I want to create a 320x200 QImage that I keep updating with setPixel commands. The QImage should be shown on screen and updated whenever something has changed. The could could for example look like this:

QImage image (320, 200, QImage::Format_Indexed8);
while (true) {
    image.setPixel (rand() % 320, rand() % 200, rand() % 16);
    [show updated image]
}

Do I need to have an event handler etc. to realize this, or is it possible to just have such a simple endless loop in the main program?

Answer 1

A infinite loop in your application's main thread will block the core application to process any GUI events. The simplest way to perform the operation frequently is to use a QTimer:

#include <QTimer>

// you can start the timer in your main window constructor
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    // define `image` as a MainWindow member in your .h
    image = QImage(320, 200, QImage::Format_Indexed8);
    QTimer *t = new QTimer(this);
    connect(t, SIGNAL(timeout()), this, SLOT(changeImage()));
    t->setInterval(100);  // ex: a 100ms interval
    t->start();
}

void MainWindow::changeImage() {
    image.setPixel (rand() % 320, rand() % 200, rand() % 16);
}

As your.h would look like this:

#include <QImage>

class MainWindow : public QMainWindow
{
    // ...
    private:
       QImage image;
    private slots:
       void changeImage();
}