#include <QtWidgets/QApplication>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QMdiArea>
#include <QtWidgets/QMdiSubWindow>
#include <QtOpenGL/QGLWidget>
#include <QtCore/QMetaObject>

class GLWidget : public QGLWidget
{
public:
    GLWidget(QWidget* parent) : QGLWidget(QGLFormat(QGL::SampleBuffers), parent) {}
    void initializeGL()
    {
        glClearColor(0.f, 0.f, 0.f, 1.f);

    }
    void paintGL()
    {
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
        glLoadIdentity();
        glTranslatef(0.0, 0.0, -5.0);
        GLfloat triangle[] = {0.0, 1.0, -3.0, 1.0, 0.0, -3.0, -1.0, 0.0, -3.0};
        glEnableClientState(GL_VERTEX_ARRAY);
        glColor4f(1.0, 0.0, 0.0, 1.0);
        glVertexPointer(3, GL_FLOAT, 0, triangle);
        glDrawArrays(GL_TRIANGLES, 0, 9);
        glDisableClientState(GL_VERTEX_ARRAY);

    }
    void resizeGL(int width, int height)
    {
        glViewport(0, 0, (GLint)width, (GLint)height);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(-5, +5, -5, 5, 0.0, 10.0);
        glMatrixMode(GL_MODELVIEW);
    }
};

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    QMainWindow main;
    QMdiArea mdi(&main);
    main.setCentralWidget(&mdi);
    main.show();
    QMainWindow sub(&main);
    mdi.addSubWindow(&sub);
    GLWidget glw(&sub);
    sub.setCentralWidget(&glw);
    sub.show();
    mdi.tileSubWindows();
    return app.exec();
}