main.cpp

#include "mainWindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainWindow.cpp

#include "mainWindow.h"
#include "gl/GLU.h"


MainWindow::MainWindow(QWidget *parent)
{
    setSurfaceType(QWindow::OpenGLSurface);

    QSurfaceFormat format;
    format.setProfile(QSurfaceFormat::CompatibilityProfile);
    format.setVersion(2, 1);
    setFormat(format);

    context = new QOpenGLContext;
    context->setFormat(format);
    context->create();
    context->makeCurrent(this);

    openGLFunctions = context->functions();

    QTimer *timer = new QTimer(this);
    connect(timer, SIGNAL(timeout()), this, SLOT(UpdateAnimation()));

    timer->start(100);
    rotation = 0;
}


MainWindow::~MainWindow()
{
}

void MainWindow::initializeGL()
{
    glEnable(GL_DEPTH_TEST);
    resizeGL(this->width(), this->height());
}

void MainWindow::resizeGL(int w, int h)
{
    // glMatrixMode(GL_PROJECTION);
    // glLoadIdentity();
    //
    // glViewport(0, 0, w, h);
    // qreal aspectratio = qreal(w) / qreal(h);
    // glOrtho(-1 * aspectratio, 1 * aspectratio, -1, 1, 1, -1);

    //set viewport
    glViewport(0, 0, w, h);
    qreal aspectratio = qreal(w) / qreal(h);

    // initialize projection matrix
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    gluPerspective(45, aspectratio, 0.1, 4000000);

    // initialize model view matrix
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void MainWindow::paintGL()
{
    glClearColor(0.39f, 0.58f, 0.93f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glTranslatef(0.0, 0.0, -3.0);
    glRotatef(rotation, 1.0, 1.0, 1.0);


    // FRONT
    glBegin(GL_POLYGON);
    glColor3f(0.0, 0.0, 0.0);
    glVertex3f(0.5, -0.5, -0.5);
    glVertex3f(0.5, 0.5, -0.5);
    glVertex3f(-0.5, 0.5, -0.5);
    glVertex3f(-0.5, -0.5, -0.5);
    glEnd();

    // BACK
    glBegin(GL_POLYGON);
    glColor3f(0.0, 1.0, 0.0);
    glVertex3f(0.5, -0.5, 0.5);
    glVertex3f(0.5, 0.5, 0.5);
    glVertex3f(-0.5, 0.5, 0.5);
    glVertex3f(-0.5, -0.5, 0.5);
    glEnd();

    // RIGHT
    glBegin(GL_POLYGON);
    glColor3f(1.0, 0.0, 1.0);
    glVertex3f(0.5, -0.5, -0.5);
    glVertex3f(0.5, 0.5, -0.5);
    glVertex3f(0.5, 0.5, 0.5);
    glVertex3f(0.5, -0.5, 0.5);
    glEnd();

    // LEFT
    glBegin(GL_POLYGON);
    glColor3f(1.0, 1.0, 0.0);
    glVertex3f(-0.5, -0.5, 0.5);
    glVertex3f(-0.5, 0.5, 0.5);
    glVertex3f(-0.5, 0.5, -0.5);
    glVertex3f(-0.5, -0.5, -0.5);
    glEnd();

    // TOP
    glBegin(GL_POLYGON);
    glColor3f(0.0, 0.0, 1.0);
    glVertex3f(0.5, 0.5, 0.5);
    glVertex3f(0.5, 0.5, -0.5);
    glVertex3f(-0.5, 0.5, -0.5);
    glVertex3f(-0.5, 0.5, 0.5);
    glEnd();

    // Red side - BOTTOM
    glBegin(GL_POLYGON);
    glColor3f(1.0, 0.0, 0.0);
    glVertex3f(0.5, -0.5, -0.5);
    glVertex3f(0.5, -0.5, 0.5);
    glVertex3f(-0.5, -0.5, 0.5);
    glVertex3f(-0.5, -0.5, -0.5);
    glEnd();


    glFlush();
}

void MainWindow::resizeEvent(QResizeEvent* event)
{
    resizeGL(this->width(), this->height());
    this->update();
}

void MainWindow::paintEvent(QPaintEvent* event)
{
    paintGL();
}

void MainWindow::UpdateAnimation()
{
    rotation += 10;
    this->update();
}

mainWindow.h

#pragma once
#include <QtOpengl>

class MainWindow : public QOpenGLWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
protected:
    virtual void initializeGL();
    virtual void resizeGL(int w, int h);
    virtual void paintGL();
    void resizeEvent(QResizeEvent *event);
    void paintEvent(QPaintEvent *event);

public slots:
    void UpdateAnimation();

private:
    int rotation;
    QOpenGLContext *context;
    QOpenGLFunctions *openGLFunctions;
};