How to deal with assertion in Qt OpenGL?

Question

Qt

I rewrote the example from the Qt guide, but it doesn't work.
Runs but issues an Assert and terminates forcibly.

ASSERT: "QOpenGLFunctions::isInitialized(d_ptr)" in file D:\Qt\5.13.2\mingw73_64\include/QtGui/qopenglfunctions.h, line 1092

refers to:

inline void QOpenGLFunctions::glViewport(GLint x, GLint y, GLsizei width, GLsizei height)
{
if defined(QT_OPENGL_ES_2) && defined(Q_OS_ANDROID)
    ::glViewport(x, y, width, height);
else
    Q_ASSERT(QOpenGLFunctions::isInitialized(d_ptr)); // <--
    d_ptr->f.Viewport(x, y, width, height);
#endif
    Q_OPENGL_FUNCTIONS_DEBUG
}

.pro file

QT       += core gui opengl

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = untitled
TEMPLATE = app
LIBS += -lopengl32

CONFIG += c++11

DEFINES += QT_DEPRECATED_WARNINGS


SOURCES += \
    main.cpp \
    mainwindow.cpp

HEADERS += \
    mainwindow.h

qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

main.cpp

#include "mainwindow.h"
#include <QApplication>

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

    w.resize(200,200);
    w.show();

    return a.exec();
}

mainwindow.h

#pragma once

#include <QOpenGLWidget>
#include <QOpenGLFunctions>

class MainWindow : public QOpenGLWidget, protected QOpenGLFunctions
{
    Q_OBJECT
protected:
    virtual void initializeGL   (                       );
    virtual void resizeGL       (int nWidth, int nHeight);
    virtual void paintGL        (                       );

public:
    MainWindow(QWidget *parent = nullptr);
};

mainwindow.cpp

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent /* = 0*/)
    : QOpenGLWidget(parent), QOpenGLFunctions()
{
    QOpenGLFunctions::initializeOpenGLFunctions();
}

/*virtual*/ void MainWindow::initializeGL()
{
    QOpenGLFunctions* pFunc =
            QOpenGLContext::currentContext()->functions();
    pFunc->glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
}

/*virtual*/ void MainWindow::resizeGL(int nWidth, int nHeight)
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glViewport(0, 0, (GLsizei)nWidth, (GLsizei)nHeight);
    glOrtho(0, 100, 100, 0, -1, 1);
}

/*virtual*/ void MainWindow::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glBegin(GL_QUADS);
        glColor3f(1, 0, 0);
        glVertex2f(0, 100);

        glColor3f(0, 1, 0);
        glVertex2f(100, 100);

        glColor3f(0, 0, 1);
        glVertex2f(100, 0);

        glColor3f(1, 1, 1);
        glVertex2f(0, 0);
    glEnd();
}

Answer 1

Perhaps you missed something during the rewrite, the author missed something, or something changed in Qt. Try running the appropriate example that comes with QtCreator, such as "OpenGL Window Example" or "Hello GL2 Example".

Answer 2

Stupid question, but does your video card support OpenGL 2 at all?
In Linux, you can find out by typing into the console: The
glxinfo | grep "OpenGL version"
header files for OpenGL must also be installed.