How to define the size of QT Opengl framebuffer - qt

Question

In GLFW we define the size of the Opengl framebuffer through this command.
GLFWwindow* window = glfwCreateWindow(1920, 1080, "Test Window", NULL, NULL);
This creates a opengl window of size 1920 X 1080 and the default frame buffer of Opengl is also of the same size.
How can we do the same in QT
This is how am i currently setting parameters for the opengl rendering.
QGLFormat format;
format.setDepthBufferSize(24);
format.setStencilBufferSize(8);
format.setSampleBuffers(true);
format.setSamples(4);
format.setSwapInterval(1);
QGLFormat::setDefaultFormat(format);
///////////////////////////////////// The GlWidget Class ////////////////
class GLWidget : public QOpenGLWidget
{
Q_OBJECT;
public:
explicit GLWidget(QWidget *parent = 0);
// ~GLWidget();
void initializeGL() override;
void paintGL() override;
void resizeGL(int w, int h) override;
QTimer timer;
QElapsedTimer elapsedtimer;
private:
int width;
int height;
};
///////////////////////////////////////////////////////////////////////////////////
GLWidget::GLWidget(QWidget *parent) : QOpenGLWidget(parent)
{
}
//////////////////////////////////////////////////////////////////////////////////////////
void GLWidget::initializeGL()
{
GLenum GlewInitResult;
glewExperimental = GL_TRUE;
GlewInitResult = glewInit();
if (GLEW_OK != GlewInitResult) // Check if glew is initialized properly
{
QMessageBox msgBox;
msgBox.setText("Not able to Initialize Glew");
msgBox.exec();
}
}
/////////////////////////////////////////////////////////////////////////////////////////////
void GLWidget::paintGL()
{
// Painting commands here which are opengl commands using GLEW.
glBindFramebuffer(GL_FRAMEBUFFER, 0); // Render in default framebuffer
glClear(GL_COLOR_BUFFER_BIT);
RenderCube();
}
///////////////////////////////////////////////////////////////////////////////////////////
IN the Main function
QApplication application(argc, argv);
QSurfaceFormat format;
format.setDepthBufferSize(24);
format.setStencilBufferSize(8);
format.setVersion(3, 2);
format.setProfile(QSurfaceFormat::CoreProfile);
QSurfaceFormat::setDefaultFormat(format);
return application.exec();

Answer 1

You can specify the size using QOpenGLFramebufferObject
The QOpenGLFramebufferObject class encapsulates an OpenGL framebuffer
object
The constructor accepts width and height. There are other overloaded constructors.
Look for documentation here.
https://doc.qt.io/qt-5/qopenglframebufferobject.html#QOpenGLFramebufferObject-5
Call bool QOpenGLFramebufferObject::bind() to switch from system provided default framebuffer. Call bool QOpenGLFramebufferObject::release() to get back to the default framebuffer.
example:
QOpenGLFramebufferObjectFormat format;
format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
QOpenGLFramebufferObject* frameBufferObject = new QOpenGLFramebufferObject(1920, 1080, format);
frameBufferObject->bind();